astro-ph.SR

Top Pith

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astro-ph.SR 2026-05-18 Recognition

SN 2023fyq progenitor detected as hot luminous source

by Xinyi Hong, Ning-Chen Sun +10 more

SN 2023fyq: direct detection of a Type Ibn supernova progenitor and its multi-wavelength environmental constraints

The vanished pre-explosion object and its 12-16 million year environment favor a low-mass helium star in a binary over a massive single star

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Context. Type Ibn supernovae (SNe) are characterized by narrow helium emission lines arising from ejecta-circumstellar medium interaction, yet their progenitors remain debated, with both massive Wolf-Rayet stars and low-mass helium stars in binaries proposed. Aims. We aim to directly identify the progenitor of the Type Ibn SN 2023fyq and to characterize its environment in order to constrain the progenitor's nature and evolutionary channel. Methods. We search for the SN progenitor based on pre-explosion and late-time HST and JWST images and derive its properties by fitting the spectral energy distribution. We investigate the SN environment by probing the stars, dust, ionized gas and molecular gas with a multi-wavelength dataset including HST and JWST imaging, VLT/MUSE integral-field-unit spectroscopy and ALMA CO (2--1) radio interferometry. Results. We discover a pre-explosion source at the SN position, which is consistent with a hot ($T>$15000 K) and luminous (log($L$/$L_\odot$) $\gtrsim$ 5.5) SN progenitor and a possible host star cluster. The progenitor is confirmed to have disappeared after explosion. Analysis of the SN environment implies that the progenitor likely has an age of log($t$/yr) = 7.1--7.2. These phenomena disfavor a very massive single-star progenitor and instead support a binary scenario involving a low-mass helium star and a compact object; the observed progenitor emission likely arises from binary interaction that began at least $\sim$12 yr before the explosion. Conclusions. SN 2023fyq is the first Type Ibn SN with a directly detected progenitor and a possible host star cluster. It adds to the diversity of Type Ibn SNe in terms of their progenitor channels and mass-loss mechanisms.

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astro-ph.SR 2026-07-03

β PsA luminosity overstated 48% as pole-on rapid rotator

by Colin Kane, Russel White +7 more

The Debris Disk Host β Piscis Austrinus is a Rapidly Rotating Star Seen Nearly Pole-On

Spectral modeling finds 4.75-degree inclination, 24% pole-equator temperature contrast, and true luminosity of 26.2 solar units for this 2.2

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Previous studies of $\beta$ Piscis Austrinus (PsA) have speculated that the narrow and saddle-like shapes of some of its weak metallic lines are a consequence of it being a rapidly rotating star viewed nearly pole-on. Here we use the \texttt{fastrot-spec} spectral synthesis code to model high-dispersion (R = 115,000) HARPS spectra of $\beta$ PsA in order to determine its inclination and photospheric properties, with additional constraints on the surface temperature set by measures of Fe II/Fe I line ratios. The analysis confirms that $\beta$ PsA is oriented nearly pole-on ($i = 4.75^{+0.75}_{-0.50}$$^o$) and experiences substantial gravity darkening caused by its rapid rotation ($\Omega/\Omega_{crit}=0.93\pm0.17$). $\beta$ PsA has a polar temperature of $10300^{+200}_{-250}$ K that is 24% hotter than its equatorial temperature ($8275^{+317}_{-400}$ K). This results in its apparent luminosity being 48% larger than its actual luminosity of 26.2$^{+1.9}_{-2.4}$ L$_\odot$. When this methodology is applied to high-dispersion spectra of the star Vega, the analysis determines a nearly pole-on orientation that is consistent with interferometric measurements, validating the technique. Based on comparisons with PARSEC evolutionary models of stars rotating at similar velocities, $\beta$ PsA has a mass of $2.20\pm0.03$ M$_{\odot}$ and an age of $141^{+113}_{-49}$ Myr; this age is consistent with the age inferred for its G5V companion star, CD-32 17127, based on lithium depletion models. The analysis demonstrates the potential for both identifying and determining the stellar properties of rapidly rotating stars viewed nearly pole-on via spectroscopy alone.

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astro-ph.SR 2026-07-03

Opacity table swaps shift Cepheid model period and growth

by Zuhoor Elahi, Christopher Sirola +1 more

Native-Opacity Sensitivity of a Fixed Delta Cephei MESA-RSP Pulsation Model

In one fixed 5-solar-mass delta Cephei run, three native MESA tables change the 500-cycle period by tens of seconds and amplitude growth by

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Radiative opacity is one of the central microphysical inputs controlling the thermal response of Cepheid envelopes and the driving or damping of radial pulsations. We present a controlled opacity-sensitivity experiment for a fixed delta Cephei nonlinear radial pulsation model computed with the MESA Radial Stellar Pulsation module. The stellar and pulsation parameters are held fixed at M = 5.0 solar masses , Teff = 6050 K, L = 2360 solar luminosities , X = 0.73, Z = 0.007, and RSP_alfam = 0.425, while the high-temperature opacity source is varied among native MESA opacity configurations: OPAL-A09, OP-A09, and OPLIB-AGSS09. The low-temperature opacity prefix, C/O-dependent opacity prefix, and all other RSP parameters are kept fixed so that the comparison isolates the effect of the adopted high-temperature opacity table. Verification integrations were performed at 20, 100, and 300 pulsation cycles, followed by photo-restarted continuations to 500 cycles. At 500 cycles, OPAL-A09 gives the closest period agreement, PRSP = 5.366986 d, only about 39 s longer than Pobs = 5.366531 d. OP-A09 gives the largest amplitude-growth diagnostics, with Delta Mag = 0.037307 and Delta R = 0.293677, corresponding to increases of 42.5% and 43.9% relative to OPAL-A09. OPLIB-AGSS09 gives a systematically longer period, P_RSP = 5.403926 d, with more modest amplitude-growth changes. The same ordering is reflected in the MESA history-column diagnostic rsp_GREKM, defined by the MESA defaults as the fractional growth of kinetic energy per pulsation period. These results show that native opacity choice measurably affects period matching, pulsation growth diagnostics, and nonlinear amplitude growth in this fixed {\delta} Cephei model. However, the tested opacity choices do not by themselves resolve the known observed-amplitude discrepancy.

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astro-ph.SR 2026-07-03

Clavius report caps 1567 solar radius at modern value

by Hisashi Hayakawa, Mitsuru Sôma +5 more

Analyses on Christoph Clavius' Reports of Total Solar Eclipses in 1560 and 1567: Key References for the Centennial Variations of the Earth's Rotation Speed and the Solar Radius

Revised Delta T bounds from 1560 and 1567 eclipses exclude linear shrinkage but allow oscillations

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Variations in solar radius (hereafter R_Sun) is a key reference for solar magnetic activity in time. The sunlight amount may have varied with R_Sun and had an effect on the Earth's climate in the past. Eclipse observations offer a unique opportunity to measure the absolute R_Sun value before modern direct observations. The scientific community has discussed a possible long-term R_Sun variability from 1715 onward. Prior to their coverage, Clavius' eclipse reports had been subjected to qualitative debates regarding the local eclipse visibility and a possible secular R_Sun trend. This study leverages the recent dramatic developments of lunar topography data and ephemeris data to provide an effective resolution of this debate. Clavius' eclipse reports described an explicit totality in 1560 at Coimbra and a "slender circle" around the eclipsing Moon in 1567 at Rome. Our study revised the {\Delta}T constraints of -492 s =< {\Delta}T =< 200 s in 1560 and 140 s =< {\Delta}T =< 151 s in 1567 to satisfy Clavius' descriptions, considering the lunar limb profile and assuming Auwers' canonical R_Sun. This study constrains the R_Sun margin of 1567, utilising three scenarios to interpret Clavius' account. The local totality requires an upper R_Sun limit of 1567 as R_Sun =< 696200 km in absolute size (959.92" in angular size), indicating no linear secular R_Sun shrinkage but possible R_Sun oscillations on a centennial timescale. Conversely, the annularity scenario is considered unlikely because it requires an R_Sun decrease of 7.5" within 3 centuries, even beyond the capacity of extreme shrinking-Sun hypotheses.

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astro-ph.HE 2026-07-03

Five Type IIP supernovae define slow-rise high-velocity subclass

by Sondos Mohsen-Tanev, Iair Arcavi +18 more

SN 2020bij and a Possible Slow-Rise High-Velocity Subclass of Type IIP Supernovae

Models attribute their light curves to weak circumstellar interaction, offering a new probe of red supergiant mass loss.

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Mapping how the explosion properties of Type II supernovae (SNe II) relate to the properties of their progenitors can provide strong constraints for understanding the final evolutionary stages of massive stars. Type IIP SNe, linked to the explosions of single red super-giant (RSG) stars, have recently been found to require some form of interaction with circumstellar material (CSM) to reproduce the rapid rise to the plateau often seen in their light curves. In this work, we present observations and analysis of the Type IIP SN 2020bij, characterized by a slow rise to its plateau as well as high expansion velocities. We identify four other SNe IIP from the literature (ASASSN-14kg, SN 2018fif, SN 2021yja and SN 2023axu) with similarly slowly rising light curves and find that they also show high expansion velocities. Using both analytical and numerical models, all five events can be explained with weak to no CSM interaction. We therefore propose that these events constitute a new subclass of Type IIP SNe which could be associated with relatively confined CSM. Early and dense photometric coverage of future SNe IIP together with early spectroscopic observations will further map this subclass and its physical properties. Understanding such rare events could be key to constraining the diversity of late-stage mass-loss in RSGs.

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astro-ph.SR 2026-07-03

Sulfur oxides detected in B[e] supergiant ejecta

by C. Bordiu, J. Ricardo Rizzo +13 more

Discovery of sulfur oxides in the ejecta of a B[e] supergiant

SO and SO2 abundances match models in 10,000 years; low 32SO/33SO ratio attributed to UV photochemistry.

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B[e] supergiants represent a rare class of luminous, evolved massive stars surrounded by dusty circumstellar disks. Since their intense UV fields were long thought to sterilize their surroundings, molecular detections beyond carbon monoxide have remained elusive, leaving their chemical reservoirs largely unexplored. Whether these environments can sustain a complex molecular chemistry is a fundamental question with significant astrochemical implications. Here we report the detection of chemically rich molecular gas surrounding the B[e] supergiant HD~87643, using ALMA observations. Our data reveal the presence of the sulfur oxides SO and SO$_2$ and other sulfur-bearing species, marking the first detection of these molecules in an early-type evolved massive star. We find a high fractional abundance of SO$_2$ relative to H$_2$, which our chemical modelling can reproduce in timescales as short as $\sim$10$^4$ yr in an oxygen-rich environment. These results indicate that the detected molecules trace a short-lived, rapidly evolving phase of out-of-equilibrium chemistry. Furthermore, we measure an anomalously low $^{32}$SO/$^{33}$SO, that we attribute to mass-independent fractionation driven by intense photochemistry. This mechanism mirrors processes proposed to explain the $^{33}$S excesses in the atmosphere of the Archaean Earth. Our findings suggest that B[e] supergiants could serve as unique laboratories for studying sulfur chemistry under extreme radiation conditions, opening potential avenues to investigate the fractionation processes that shaped the isotopic signatures found in the early geological record.

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astro-ph.SR 2026-07-03

TESS revises IR Cas to 1.32 and 1.05 solar mass main-sequence pair

by Matúš Kamenec, Pavol Gajdoš +4 more

Revision of the Detached Eclipsing System IR Cas from TESS Observations, Ground-Based Photometry and Spectroscopy

Timing variations point to a possible third body on a 38-year orbit while stars match standard evolution tracks.

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We present a new photometric and spectroscopic analysis of detached eclipsing binary IR Cas based on TESS observations, supplementary ground-based photometry in Sloan $g^\prime$, $r^\prime$, and $i^\prime$ filters, and newly obtained radial velocity measurements. The updated orbital and physical parameters of the system were derived using combined light-curve and radial-velocity modeling. The resulting solution indicates that both components are main-sequence stars with masses of approximately $1.32$ M$_{\odot}$ and $1.05$ M$_{\odot}$. We investigated in detail the fact, that the TESS light curves exhibit asymmetries near the maxima, which were reproduced by introducing a cool spot that moves on the surface of the secondary component. Long-term analysis of times of minima revealed quasi-periodic variations in the O$-$C diagram that can be interpreted as a light-time effect due to a possible third body with an orbital period of about 38 years. The positions of both components in the mass-radius diagram agree well with empirical relations for detached main-sequence binaries and do not indicate substantial deviations from standard stellar evolution. Overall, IR Cas appears to be an evolutionarily representative detached eclipsing system with moderate indications of stellar activity.

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physics.space-ph 2026-07-03

Four Solar Orbiter shocks show energetic particles exceeding thermal plus magnetic pressur

by D. Trotta, D. Lario +11 more

Energetic particle-mediated interplanetary shocks observed by Solar Orbiter

The events are strong and fast, with particle-dominated regions extending up to 100000 ion inertial lengths upstream.

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Context: In collisionless shocks, energetic particles can carry sufficient pressure to modify the upstream plasma and the shock structure itself, a regime often invoked in theories of cosmic-ray acceleration but rarely observed in the heliosphere. Aims: We find and characterize {interplanetary} IP shocks where energetic particles dynamically dominate the upstream pressure. Methods: We analyze IP shocks observed by Solar Orbiter inside 1 au and compute the energetic particle pressure $P_{EP}$ from proton measurements above 10\,keV, comparing it with the upstream thermal $P_{Th}$ and magnetic $P_{B}$ pressures. Results: We identify four shocks for which $P_{EP} \geq P_{Th} + P_B $. These events correspond to strong and fast shocks in the high-Mach-number tail of the Solar Orbiter shock population. In several cases the $P_{EP}$ increase coincides with a decreasing upstream bulk flow speed in the shock frame, and the resulting particle-mediated foreshocks extend up to $\sim10^5$ {ion inertial lengths} $d_i$. The extent of such energetic particle dominated region depends on shock geometry. Conclusions: These observations provide evidence that accelerated particles can dynamically modify interplanetary shocks. They highlight the importance of the coupling between energetic particles, upstream fluctuations, and shock structure for understanding particle acceleration at collisionless shocks.

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astro-ph.SR 2026-07-03

Small-scale dynamo generates majority of quiet Sun magnetic energy

by Wen-Jie Jiang, Lei Ni +3 more

Research Progress on Solar Small-Scale Dynamo

Review of data and models finds local turbulence sustains cycle-independent fields that affect the corona, wind, and radiation.

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The small-scale solar dynamo theory, as the core mechanism explaining the origin of the persistent, disperse weak magnetic field in the quiet Sun regions, has made significant progress over the past three decades in the fields of observation, theory, and simulation. Breakthrough observations from high-resolution space-based and ground-based telescopes have revealed that the quiet Sun is ubiquitously populated by highly dynamic, mixed-polarity and possibly predominantly horizontal magnetic structures with complex topology. These observations confirm that their total magnetic flux is substantial, with a high and widely distributed magnetic flux emergence rate, strongly suggesting a local dynamo effect independent of the solar cycle and driven by intense turbulence and convection. Theoretical studies indicate that even in the challenging low magnetic Prandtl number ( Pm << 1) environment of the solar photosphere and convection zone, turbulent motions can self-excitedly convert kinetic energy into magnetic energy through the stretching, folding, and twisting of magnetic field lines. MHD simulations have successfully reproduced observed features, demonstrating that a pure small-scale dynamo can operate efficiently and sustain magnetic fields even in an open, stratified solar environment incorporating realistic physical processes. Current research strongly suggests that small-scale magnetic fields constitute the majority of the magnetic energy in the quiet Sun and also influence coronal heating, solar wind acceleration, and radiation distribution. This article conducts a literature review centered on observations, theoretical models, and numerical simulations of the small-scale dynamo, organizing and discussing the relevant research history and progress. Finally, it summarizes the content and provides an outlook on future research from multiple perspectives.

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astro-ph.SR 2026-07-03

Atmospheric overflow stabilizes symbiotic mass transfer to q=1.5

by Tan Liu, Natalia Ivanova +6 more

Revisiting atmospheric Roche lobe overflow in symbiotic binaries

Models predict million-year interaction phases that match the long-lived S-type systems seen in the Galaxy.

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Classical binary evolution models predict dynamically unstable mass transfer in symbiotic stars with high mass ratios, leading to a common envelope. However, many observed S-type symbiotic systems show long-lived interaction, suggesting that an additional stabilizing mechanism may be at work. We investigate whether atmospheric Roche-lobe overflow can prolong the mass-transfer phase and help reconcile theory with observations. We implement the Rapid Unified Mass Transfer framework in \texttt{MESA} and compute a grid of white-dwarf--giant binaries covering a wide range of donor masses, mass ratios, and orbital periods. We then compare the resulting lifetimes and evolutionary tracks with well-constrained Galactic S-type symbiotic systems. For convective giant donors, our models recover stable mass transfer up to $q \simeq 1.5$, while atmospheric overflow strongly extends the symbiotic phase. RGB and early-AGB systems with $q \lesssim 1.5$ can remain interacting for up to $10^6$ yr at $\dot{M} \gtrsim 10^{-9},M_{\odot},{\rm yr}^{-1}$, much longer than the commonly assumed $\sim 10^3$ yr pre-common-envelope lifetime. In these systems, the orbit shrinks mildly and may re-expand after mass-ratio reversal. Systems with higher mass ratios still evolve toward a common envelope, but even for $q \simeq 2$--$4$ the symbiotic phase can last $10^4$--$10^5$ yr. The synthetic distribution in the orbital-period--mass-ratio plane and individual evolutionary tracks are broadly consistent with observed S-type symbiotic binaries, including recurrent novae. The RUMT framework, which incorporates atmospheric RLOF, provides an explanation for the long-term stability of many symbiotic binaries and may account for their high observed occurrence rate.

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astro-ph.SR 2026-07-03

Sun's chemical differences mostly trace to galactic evolution

by Mia Babatsikos, Fan Liu +6 more

The Sun's chemical peculiarity: disentangling Galactic chemical evolution and planetary engulfment in solar twins

Bayesian separation of 79 solar twins attributes 62 percent of patterns to GCE, leaving 2-6 possible engulfment cases

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Recent observational studies have suggested that the Sun may be chemically peculiar relative to the majority of solar twins. Here, we re-analyse high-resolution, high signal-to-noise spectra of 79 nearby solar twins using a differential spectroscopic approach and Bayesian framework to test whether the Sun's chemical peculiarity arises from Galactic chemical evolution (GCE) or planetary ingestion. Using the spectroscopic tool \texttt{Korg}, we obtain highly precise, validated atmospheric parameters and abundances for 18 elements, with an average abundance precision of 0.015\,dex (3.5\%). Employing an independent Bayesian indicator, we disentangle GCE and planetary engulfment signatures from other processes influencing stellar composition, including intrinsic abundance scatter. Our results indicate that the chemical peculiarity of the Sun relative to the average solar twin is largely driven by GCE effects, with 62.3$\pm$5.8\% of our sample exhibiting abundance patterns well-described by GCE trends. We further identify 2--6 solar twin candidates exhibiting chemical signatures consistent with planetary engulfment that warrant further investigation. These findings reinforce the importance of accounting for GCE effects when interpreting solar twin abundance patterns, and suggest that the Sun may not be chemically peculiar relative to the majority of solar twins.

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astro-ph.SR 2026-07-03

Unsteady solar flare loop-tops accelerate electrons more efficiently

by Yoshiaki Sato, Takafumi Kaneko +2 more

Numerical Investigation of Efficient Electron Acceleration at an Unsteady Solar Flare Loop-Top

Time-varying fields enable betatron gains at edges where steady fields suppress net acceleration via cooling

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Using magnetohydrodynamic (MHD) fields and guiding-center test-particle calculations, this study investigates how time-dependent loop-top dynamics modulate the adiabatic energization of electrons in a solar flare. Our results indicate that a time-varying loop-top structure enhances acceleration efficiency compared to a quasi-steady one. In the quasi-steady velocity field, the net acceleration is suppressed due to the decelerating effect of betatron cooling. Conversely, in the unsteady velocity field, the betatron mechanism readily accelerates electrons within the compressed magnetic field at the edge of the loop-top. These findings suggest that the acceleration of electrons at the loop-top is driven not only by the static shape of the magnetic structure but also by dynamic events such as plasmoid collisions. While previous studies have primarily focused on acceleration processes within the reconnection outflow, such as at termination shocks or within plasmoids, our research highlights the importance of the acceleration and deceleration processes at the exit point where electrons escape from the loop-top.

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astro-ph.SR 2026-07-03

Ions and neutrals slip by 15 km/s in solar prominence eruption

by Yuwei Huang, Kiyoshi Ichimoto +1 more

Detection of Doppler velocity differences between ions and neutrals in an erupting prominence

Spectroscopy of Ca II, He I and O I lines shows decoupling under 150g acceleration and offers a diagnostic for hydrogen ionization.

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We performed a spectroscopic observation of an erupting prominence occurred on the solar limb on 2015 May 8th in He I 706.5 nm, O I 777.2 nm triplet and Ca II 849.8 nm lines to investigate differences in the Doppler velocity between ions and neutrals in a plasma strongly accelerated by the Lorentz force. We found that the ion-neutral velocity difference between Ca II and He I reached an order of 15 km s-1. On the other hand, the velocity difference between Ca II and O I was significantly smaller than that between Ca II and He I. This result can be interpreted as the formation of O I 777.2 nm lines in the erupting prominence is mainly contributed by the recombination from O II ions through charge transfer with hydrogen atoms, resulting in a behavior close to ions. According to an order estimate of the collisional friction among He I atoms and protons, the observed velocity difference between Ca II and He I implies the acceleration of the eruption reaching about 150 times of solar gravity. We propose a new method to evaluate the ionization degree of hydrogen from the velocity differences observed in Ca II, He I and O I lines.

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astro-ph.SR 2026-07-02

Hyperbolic paths refine Stark profiles for ionized helium

by Patrick Tremblay, Alain Beauchamp +1 more

Stark-Broadened Profiles for Ionized Helium Lines Using Computer Simulations

Simulations for the He II 4686 line replace straight-line assumptions to capture charged-emitter interactions

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We present new and improved calculations of Stark-broadened profiles for ionized helium, a key ingredient in the spectroscopic analysis of helium-atmosphere DO white dwarfs. Our approach builds upon the computer simulation framework previously developed for neutral helium, which fully accounts for the dynamical interactions of both ions and electrons with the emitting helium atom. We extend this theoretical formalism by relaxing the assumption of straight-line trajectories for the perturbing particles (electrons and ionized helium) and adopting the hyperbolic trajectories appropriate for their interaction with a charged emitter, thereby accounting for their dynamical influence on the line-broadening process. In this exploratory study, we focus on the He II 4686 line, the strongest absorption feature observed in the spectra of DO white dwarfs. We present the resulting Stark profiles and perform a detailed comparison with those available in the literature.

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astro-ph.EP 2026-07-02

JWST detects methane on a white dwarf planet

by Ryan J. MacDonald, Christopher E. O'Connor +16 more

Aerosols and hydrocarbons in the atmosphere of a white dwarf planet

The spectrum indicates the planet was reheated by migration 3-5.5 billion years after the star became a white dwarf.

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Most stars, including our Sun, will one day evolve into red giants and, subsequently, white dwarfs. Several planet candidates have recently been identified orbiting white dwarfs, demonstrating that planets can survive the stellar post-main-sequence stage intact. Little is known about the atmospheric composition of post-main-sequence planets, with the most evolved transiting planets with atmospheric detections to date orbiting subgiants. Here we report an atmospheric detection for the white dwarf planet WD 1856 b, achieved through transmission spectroscopy with the JWST NIRSpec PRISM. Our 0.5-5.0 $\mu$m spectrum reveals the presence of hydrocarbons (odds ratio of $167:1$ to $5377:1$, with $\mathrm{CH}_4$ preferred at $17:1$ to $30:1$), aerosols ($2 \times 10^5:1$ to $2 \times 10^6:1$), and thermal emission from the planetary nightside ($2 \times 10^{63}:1$ to $2 \times 10^{73}:1$). Our spectral analysis constrains WD 1856 b's mass to $4.3$ to $10.9 \mathrm{M}_J$, finds a carbon-enriched atmosphere (with a $\mathrm{CH}_4$ abundance of $\approx 7\%$), and an effective temperature exceeding the expected planetary equilibrium temperature ($390$ to $412 \, \mathrm{K}$ vs. $160 \, \mathrm{K}$). Based on cooling models, these results suggest that WD 1856 b underwent a migration-related reheating event $3.0$ to $5.5 \, \mathrm{Gyr}$ into the white dwarf phase, consistent with post-main-sequence tidal evolution to the present-day $0.02 \, \mathrm{au}$ circular orbit. Our results provide a window into the ultimate fate of giant planets orbiting stars with masses similar to our Sun.

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astro-ph.SR 2026-07-02

Pipeline detects four times more filament oscillations than manual search

by Guillem Castelló, Manuel Luna +1 more

Automatic detection of solar filament oscillations I: Multi-scale spectral pipeline

Multi-scale analysis of GONG H-alpha images recovers known events and finds 69 additional ones in two weeks of data.

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Solar filament oscillations provide important diagnostics of prominence magnetic structure and stability, but their detection in long H\alpha archives has traditionally relied on visual inspection, manually placed slits, and time--distance diagrams. We present an automatic pipeline for detecting spatially coherent filament oscillations in GONG H\alpha image sequences. The method combines image preprocessing and coalignment, deep-learning-based filament detection and segmentation, multi-scale spatial averaging, Lomb--Scargle spectral analysis, convolutional-neural-network background estimation, empirical calibration of significance thresholds, and clustering of candidate detections in period and space. Only oscillations supported across at least four spatial scales are retained, reducing sensitivity to local pixel-scale intensity fluctuations. The pipeline recovers several events from the manual GONG catalog of Luna et al. (2018), including the 1 January 2014 oscillation with a period of approximately 76 min. Applied to the first two weeks of January 2014, it identifies 91 oscillatory events, compared with 22 non-duplicate events in the corresponding manual catalog, with detected periods ranging from about 20 to 126 min. It also detects previously unreported oscillations, including an event on 13 January 2014 with a period of approximately 86 min that is independently confirmed using a conventional time--distance diagram. These results demonstrate that automated filament segmentation, multi-scale spectral analysis, and calibrated significance testing can provide a reproducible and scalable alternative to manual slit-based searches. The pipeline substantially increases detection sensitivity while preferentially selecting coherent filament-scale oscillations, enabling future statistical studies over extended GONG intervals and across the solar cycle.

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astro-ph.EP 2026-07-02

TOI-2134 outer planet has 59-degree obliquity and eccentricity 0.31

by Federica Rescigno, Manu Stalport +29 more

Understanding eccentric temperate giants: an in-depth study of the architecture and stellar obliquity of the TOI-2134 system

New TESS sectors and 280 radial velocities fix the orbits of an inner mini-Neptune and outer eccentric sub-Saturn.

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We revisit the TOI-2134 planetary system with three new high-cadence TESS sectors and 98 more spectra. This new analysis confirms the two orbiting planets by simultaneously modelling a total of eight sectors of corrected TESS photometry and 280 HARPS-N and SOPHIE radial velocities: an inner mini-Neptune in a near-circular $9.229198\pm0.000003$ days orbit, and an outer temperate sub-Saturn orbiting with a $95.852840\pm0.000042$ days period and eccentricity of $0.31\pm0.01$. The masses and radii of the planets were computed to be $9.37\pm0.54$ Me and $2.735\pm0.068$ Re for planet b, and $58.3\pm1.9$ Me and $7.35\pm0.18$ Re for planet c. The new data not only improves the detection significance and precisions on the planetary orbits, but also breaks the original multimodality in the eccentricity solution for the outer planet. We also detect a long-term trend in the radial velocity data, which we attribute to a stellar magnetic cycle. We investigate the spin-orbit alignment of the system via observations of the Rossiter-McLaughlin effect for TOI-2134~b with EXPRES and TOI-2134~c with PARAS-2. No RM effect was detected for planet b, but we find a 4.7$\sigma$ detection of a $59\pm31^{\circ}$ obliquity for planet c. Finally, we examine the architecture of the system, assess its completeness, investigate the planetary interior, and their suitability for follow-up atmospheric analysis.

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astro-ph.GA 2026-07-02

Oxygen ratios and ages expose hidden Milky Way disk populations

by Thomas Bensby

Exploring the Milky Way stellar disk. Carbon, nitrogen, oxygen, sulphur, potassium, and copper abundances for 714 F and G dwarf stars in the solar neighbourhood

Measurements in 714 local stars show clearer old-young separations in [X/O] than in traditional [X/Fe] trends for several elements.

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[ABRIDGED] We aim to determine abundances of carbon, nitrogen, sulphur, potassium, and copper for 714 nearby F and G dwarf and subgiant stars, and to re-derive oxygen abundances using updated corrections for departures from the assumption of local thermodynamic equilibrium. These elements extend the chemical inventory of our previous studies and provide new constraints on the relative enrichment histories of the Galactic thin and thick disks. The alpha-element behaviour of oxygen is confirmed, with old stars defining an enhanced sequence relative to young stars. Sulphur closely follows oxygen, while potassium shows broadly alpha-like behaviour in [K/Fe] but residual trends relative to oxygen. Carbon and nitrogen show only modest separation in [X/Fe], but much clearer population differences in [X/O]. Copper displays a strong metallicity dependence and clear separation between old and young populations when compared to oxygen. We also find that [O/Mg] is not constant, demonstrating that oxygen and magnesium provide complementary rather than interchangeable reference scales. Quantitative comparisons of all elements analysed in our studies show that carbon, oxygen, sulphur, and potassium rank among the most age-sensitive abundance ratios in the sample and provide strong discrimination between old and young disk populations. The new abundance measurements substantially expand the diagnostic power of this local stellar sample. The results show that abundance ratios relative to oxygen, together with precise stellar ages, reveal population differences that are partly hidden in traditional [X/Fe] trends. The expanded abundance inventory provides a homogeneous reference dataset for studies of Galactic chemical evolution, Galactic archaeology, and large spectroscopic surveys.

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astro-ph.HE 2026-07-02

SKAO surveys to discover thousands of pulsars

by Bhal Chandra Joshi, Aris Karastergiou +1 more

Pulsar Science with the SKAO

High-sensitivity telescopes will support deep observations feeding tests of gravity, nano-Hz waves and nuclear matter.

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The large instantaneous sensitivity, wide frequency coverage and flexible observation modes, with large number of beams in the sky, are the main features of the SKA observatory's two telescopes, the SKA-Low and the SKA-Mid. Owing to these capabilities, the SKAO telescopes are going to be a game-changer for radio astronomy in general and pulsar astronomy in particular. Eleven chapters in this book describe their impact on different areas of pulsar science. In this overview article each chapter is briefly summarised and the inter-relationship between different pulsar science use cases are explored: new deep surveys, covering the Galactic field, globular clusters and the Galactic centre, will discover thousands of new pulsars; these will form the backbone for studies of neutron star physics and of their environments. The enhanced understanding provided by these studies will feed into the main contributions to fundamental physics from pulsar astronomy: testing relativistic gravity, studying gravitational waves in the nano-Hz regime and studying the equation of state of nuclear matter. Synergies with other science cases are also highlighted throughout this overview.

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astro-ph.CO 2026-07-02

Oldest Milky Way stars reach 13.73 Gyr

by Indranil Banik, Thenujaya Kudakolawa Kaluarachchige +2 more

The age of the Universe from a large sample of the oldest Galactic stars

Large spectroscopic sample yields age consistent with 13.6 Gyr Lambda-CDM but inconsistent with 12.9 Gyr pre-recombination Hubble-tension mo

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We estimate the age of the Universe using the Xiang & Rix sample of 247,103 Milky Way stars with high-resolution spectroscopy from LAMOST DR7 and $Gaia$ eDR3 parallaxes. Stellar ages were estimated using YY isochrones up to 20 Gyr. To remove stars with unusually high and precise ages, we require old stars to be metal-poor and $\alpha$-enriched. We also require consistency between YY ages and those obtained with FLAME based only on $Gaia$ data. Our final sample of 155,600 stars within 5 kpc provides consistent cosmic age estimates using several techniques of increasing rigour. Our main results use an MCMC reconstruction of the latent age distribution, though our iterative reconstruction is very similar. Applying an innovative approach to our MCMC reconstruction and its uncertainties, we find that the oldest star has an age of $A_\star = 13.73^{+0.18}_{-0.15}$ Gyr. Varying the quality cuts can at most reduce this to $A_\star = 13.31^{+0.21}_{-0.18}$ Gyr or raise it to $14.02^{+0.18}_{-0.15}$ Gyr using a much lower or higher age-dependent metallicity ceiling, respectively. Our inferred $A_\star$ is consistent with the 13.6 Gyr expected in CMB-calibrated $\Lambda$CDM, assuming the first long-lived stars formed when the Universe was 0.2 Gyr old. This agreement casts doubt on solutions to the Hubble tension solely through new physics prior to recombination, which generally imply a cosmic age of $12.9 \pm 0.2$ Gyr to match low redshift probes. It is difficult for stellar modelling uncertainties to reconcile such a low age with our result given the low metallicities of the oldest stars in our sample and independent asteroseismic constraints.

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astro-ph.SR 2026-07-02

SKA to detect nonthermal emissions from quiet solar corona

by Surajit Mondal, Divya Oberoi +5 more

Unravelling the nonthermal emissions from the quiet solar corona with the SKA

Sensitivity and resolution will link weak radio sources to thermal structures and test energy partition.

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Investigation of the nonthermal emissions from the quiet solar corona has been rather limited. This primarily stems from the fact that the emission is expected to be quite weak and very high dynamic range images are required to detect such emissions. Although, the few detections of the nonthermal emissions have all come from the radio band, the past observations had several issues, the most important being the low image fidelity and lack of simultaneous broadband observation capability. Recent observations have been able to tackle many of these prior difficulties using modern instrumentation, and have produced multiple interesting results. In spite of these improvements, multiple challenges remain. For example, most of the recent investigations were only able to focus on the brightest of these events, due to rather poor spectroscopic snapshot PSF of the instruments. The SKA, with its excellent sensitivity as well as its exquisite spectroscopic snapshot PSF would be a game-changer in this field. It would not only allow us to detect and characterise these emissions in Stokes I, but would also allow us to investigate their polarisation properties as well. The high angular resolution offered by the SKA will allow a unique association of the detected radio transients with their thermal counterparts. This would enable us to investigate the thermal-nonthermal energy partition even for these rather weak transient emissions, which in turn would allow validation of particle acceleration and magnetic reconnection theories in a regime vastly different from that done previously. In addition, characterization of the nonthermal emissions of these weak coronal transients may also provide a new probe to understand how energy is transferred from the photosphere and dumped into the corona, and thus serve as a new tool to tackle the coronal heating problem.

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astro-ph.SR 2026-07-02

Red giant magnetic fields carry 10% model uncertainty

by L. Buchele (1), L. Bugnet (1) +6 more

Constraining the model-based uncertainties of asteroseismic magnetic field measurements in red giants

Precise metallicity recovers the core sensitivity parameter from MESA grids, leaving observational errors dominant for most stars.

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Magnetic fields inside red giants are measured using shifts to the oscillation frequencies. However, in the asymptotic framework, converting a frequency shift into a radial magnetic field strength requires knowing the global magnetic sensitivity. This parameter (also called the core structure parameter) must be inferred from stellar models, introducing a source of uncertainty. We seek to understand how the global magnetic sensitivity depends on stellar properties such as mass and metallicity, and to quantify the model-based uncertainty on magnetic field measurements. We also explore which stellar properties are key to finding a precise and accurate estimate of the global magnetic sensitivity. Using MESA models, we examine how the global magnetic sensitivity changes with mass, metallicity, and age. We then create a set of synthetic stars and test how well we recover the sensitivity parameter. We consider different grid construction approaches and the choice of which observables are used in the fitting process. We find that the global magnetic sensitivity shows a stronger dependence on mass for higher mass models and a stronger metallicity dependence for lower metallicity models. Our approach recovers the sensitivity parameter well, with an uncertainty of 10% when precise metallicity measurements are used. We apply our method to stars with existing magnetic field measurements. In most cases, the dominant source of uncertainty remains observational, although precise modeling can significantly reduce the magnetic field uncertainty for stars with exceptional data. With careful fitting, models yield accurate values for the global magnetic sensitivity. We recommend that future work obtain the global magnetic sensitivity using both asteroseismic and high-quality spectroscopic data. Under these conditions, we recommend adopting a model-based uncertainty of 10% on the sensitivity parameter.

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astro-ph.SR 2026-07-02

Brown dwarf spectra favor weak mixing Elf Owl models

by Zafar Rustamkulov, J. Kirkpatrick +22 more

SPHEREx 0.75 to 5 μm Spectra for a Sequence of Nearby Brown Dwarfs

SPHEREx data on 37 nearby objects show clear preference for low k_zz over strong mixing despite offsets near CO features.

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The SPHEREx all-sky survey has now measured the R$\sim$40-100 infrared spectra of thousands of nearby brown dwarfs in the chemically rich 0.75-5 $\mu$m range. The survey's wide spectral coverage and high S/N permits flux measurements that capture several broadband molecular absorption features, and upwards of 80$\%$ of the total bolometric luminosity of most brown dwarfs. Atmospheric models are known to yield systematic disagreements in the inferred temperatures and radii of brown dwarfs, necessitating benchmarking against observations. In this work, we present SPHEREx spectra across a broad sequence of 37 nearby field brown dwarfs, ranging from L0 to Y4 ($\sim$2500-250 K) and compare them to theoretical expectations. We additionally compile spectra for separate low-gravity and low-metallicity objects, and show how they trend with constant spectral type. We fit the measured spectra to the well-known forward model grids Sonora Diamondback, Elf Owl, BT-Settl, ATMO2020 and ATMO2020++ and compare their goodness-of-fit as a function of wavelength, spectral type, and treatment of clouds and chemistry. We find that the models continue to struggle to simultaneously fit the J/H/K peaks and the 4 $\mu$m opacity window, especially in L/T transition objects. The largest deviations appear around the chemistry-sensitive CO$_2$ and CO features. Despite these offsets, the models broadly capture their trends across the L/T transition, with the observed sample of field dwarfs strongly preferring the weak vertical mixing ($k_\mathrm{zz}$ = 10$^4$ cm$^2$s$^{-1}$) Elf Owl models over strong mixing. The spectra shown here along with future SPHEREx data will help guide improvements to models.

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astro-ph.SR 2026-07-02

Optimal PFSS source surface radius grows in solar cycle ascent

by Shiouhe Wang, Fang Shen +3 more

Optimization Algorithm for Determining the Source Surface Radius Based on Parker Solar Probe in situ Measurements from Encounters 1 to 19

Tuning to Parker Solar Probe data improves open flux agreement while holding polarity accuracy steady

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The Potential Field Source Surface (PFSS) extrapolation is a method for estimating the large scale coronal magnetic field from photospheric magnetograms. The source surface serves as the outer boundary of its solution domain, and is typically a spherical surface. An appropriate source surface radius ($R_{ss}$) enables more accurate identification of the coronal magnetic field topology and estimation of the open flux, thereby potentially enhancing the accuracy of space weather modeling. We prove the well-posedness of the PFSS forward problem and establish the existence and uniqueness of the optimal source surface by combining compactness of the admissible set with continuity of the objective functional. The objective functional is the mean squared error (MSE) between PFSS extrapolation and Parker Solar Probe (PSP) radial magnetic field measurements after Parker spiral backmapping and radial scaling for Encounters 1-19. The optimization algorithm is validated with an analytical solution, and Advanced Composition Explorer (ACE) in situ measurements are used as an independent cross-validation dataset. Additional evaluation metrics and Pareto analysis are used to identify the dominant metrics between open flux and polarity prediction accuracy. Our results show that the optimal $R_{ss}$ derived from the algorithm generally increase from solar minimum into the ascending phase of solar cycle 25. The optimized solution improves open flux agreement while preserving or improving polarity prediction accuracy relative to $2.5R_{s}$. The Pareto frontiers show a transition for dominant metrics from open flux during solar minimum to polarity prediction accuracy during the ascending phase.

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astro-ph.HE 2026-07-02

Heavy-element dust explains late kilonova infrared glow

by Nanae Domoto, Kenta Hotokezaka +1 more

Heavy element dust explains the late-time spectra of kilonovae

Kinetic models show refractory grains from Zr, W and Os produce the emission seen below 1000 K in AT2017gfo and similar events

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Neutron star mergers are a leading site of $r$-process, producing radioactively powered optical and infrared transients known as kilonovae. Observations of the kilonovae AT2017gfo, associated with the gravitational-wave event GW170817, and AT2023vfi, associated with GRB 230307A, have enabled measurements of the mass of ejected $r$-process material and the identification of heavy elements in the ejecta. However, late-time observations reveal strong infrared emission with temperature below 1000 K, which is difficult to explain by atomic absorption and emission processes alone. In this paper, we show that kilonova ejecta provide conditions favorable for the formation of dust grains composed of refractory $r$-process elements including Zr, W, and Os. We calculate the kinetic formation of dust grains using reaction rate coefficients of W as a proxy, finding that dust forms efficiently, particularly in slow ejecta. This stands in contrast to a previous study that relied on a classical nucleation framework. By performing radiative transfer simulations that incorporate dust formation, we demonstrate that $r$-process dust naturally explains the observed late-time infrared emission. The formation and abundance of $r$-process dust are highly sensitive to the ejecta mass, composition, and expansion velocity. Infrared emission from $r$-process dust can therefore serve a new probe of heavy-element production in neutron star mergers.

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astro-ph.SR 2026-07-02

Magnetic white dwarfs more massive with pre-crystallization fields

by Larissa L. Amorim, Weligton.N. Costa Junior +4 more

White Dwarf Classification of DESI DR1 Spectra1

DESI catalog of 44,000 spectra finds higher masses and fields before crystallization, implying multiple origins.

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We present a new catalog of spectroscopically confirmed white dwarfs from the Dark Energy Spectroscopic Instrument (DESI) Data Release 1. We visually classified 44,417 white dwarf spectra and derived atmospheric parameters for 29,072 DA white dwarfs through spectroscopic model fitting. The resulting mass distribution is non-Gaussian, with a mean mass of $0.677\,M_\odot$, consistent with previous studies. We identify 547 magnetic white dwarfs by detecting Zeeman splitting, including 84 new discoveries, and estimate their magnetic field strengths using off-centered, inclined dipole models when possible. We compare our magnetic field determinations with previous measurements and find overall good agreement. Finally, we investigate the relation between stellar properties and magnetism, finding that magnetic white dwarfs are systematically more massive than the general white dwarf population and that intermediate-strength magnetic fields are already present in stars that have not yet entered the crystallization phase. This result suggests that crystallization is unlikely to be the sole mechanism responsible for the origin of magnetic fields in white dwarfs.

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physics.space-ph 2026-07-02

VLBI sessions refine deep space orbit tracking over two years

by Oliver James White, Guifre Molera Calves +3 more

VLBI Tracking of the JUICE Mission: Two Years of Cruise Phase Operations and Performance Analysis

More than 100 observations add geometric diversity for better position accuracy and spacecraft diagnostics during cruise.

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The JUpiter ICy moons Explorer (JUICE) mission, launched by the European Space Agency (ESA) in April 2023, represents one of the most ambitious deep space exploration endeavours targeting Jupiter's icy moons. This paper presents results from the Very Long Baseline Interferometry (VLBI) radio telescope tracking conducted by the University of Tasmania during the first two years of JUICE's cruise phase operations. We have conducted over 100 tracking sessions capturing the spacecraft across different orbital regimes as JUICE progresses through its complex cruise trajectory towards Jupiter. Our analysis focuses on three key areas: Doppler residual characterisation, mission performance indicator extraction, and solar wind scintillation pattern analysis (including space weather forecasting). UTAS measurements demonstrate the enhanced capabilities that VLBI networks provide for deep space mission support, particularly for precision orbit determination and spacecraft health diagnosis. The results showcase the UTAS VLBI array as a valuable complement to traditional tracking infrastructure, offering Southern Hemisphere coverage and enhanced geometric diversity for deep space missions.

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astro-ph.HE 2026-07-02

Companion interaction cannot explain asymmetric SNR expansion rates

by Jingxiao Luo, Gilles Ferrand +3 more

Three-Dimensional Simulations of Type Ia Supernova Remnants I: Effects of a Main-Sequence Companion Star

3D models of Type Ia ejecta colliding with a main-sequence star reproduce some remnant shapes but fall short on the large velocity differenc

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Type Ia supernovae (SNe Ia) serve as one of cosmic standard candles, but their exact progenitor channel is still an open question. SNe Ia commonly come from binary star evolution. Therefore, one of the major differences among the proposed progenitor channels is whether there is a more-or-less intact companion star remaining at the time of explosion, which causes the SN ejecta to be more asymmetrical. As the SN ejecta evolved into supernovae remnants (SNR), the imprint formed by the companion interaction may affect the morphology of the SNR. In addition, the progenitor systems may have experienced different mass transfer histories and therefore led to formation of different circumstellar material (CSM) environments, which may also affect the early evolution of SNR. In this study, we use GADGET and RAMSES codes to simulate these physical effects and follow the evolution into early-phases of SNRs. In our simulations, we consider different ejecta models and track the element distribution. We compare our simulation with actual observations and conclude that despite some SNRs having morphology resemblance to our simulation results, their highly asymmetric expansion rates are hard to explain by interaction between SN ejecta and a companion star alone.

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astro-ph.SR 2026-07-01

Gaia DR4 pipeline to give masses and ages for 500 million stars

by Orlagh L. Creevey, Laia Casamiquela +24 more

Stellar masses and ages in Gaia Data Release 4 from the Final Luminosity Age Mass Estimator algorithm

FLAME combines analytical luminosity-radius steps with Bayesian or minimization fitting on Gaia data to produce the estimates.

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The masses and ages of stars are key quantities for understanding exoplanetary, stellar, and galactic evolution. In the context of Gaia, these parameters provide insights into the stellar populations, helping to trace the formation and history of the Galaxy. As part of the Gaia Data Processing and Analysis Consortium (DPAC), the Final Luminosity Age Mass Estimator (FLAME) pipeline processes Gaia data to derive stellar parameters comprising luminosities, radii, masses and ages. This paper discusses the methods and data used in FLAME for Gaia Data releases and the expected performances of FLAME for the 4th Gaia Data Release. FLAME comprises two main components: the first one, which is analytical, is used to estimate luminosity, radius, and radial velocity correction due to gravitational redshift by exploiting the atmospheric, astrometric, and photometric parameters produced within Gaia. The second is a model inference based on two main approaches: a classical minimization approach, and a Bayesian framework. It aims to derive mass, age, and evolutionary stage. The two step implementation offers flexibility in handling photometric properties that are prone to systematic errors. Tests with simulated data, the Sun, and well characterised samples of stars show that the methods in FLAME perform as expected, producing results in statistical agreement with the literature. We provide new stellar fundamental parameters for some high velocity stars, stars with very low mass companions, and a selection of stars in the Plato Field of View. In Gaia Data Release 4 approximately 500 million sources will have results from the pipeline. [abridged]

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astro-ph.SR 2026-07-01

Four white dwarfs show stable metal accretion over 18 years

by Laura K. Rogers, Michael M. Shara +13 more

Spectroscopic Monitoring of Metal Lines in Polluted White Dwarfs

Line strengths in most systems vary by less than 30 percent, implying steady rates across many diffusion cycles.

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The disruption and accretion of planetary material onto white dwarfs is expected to be inherently dynamic and stochastic, potentially driving variability in the accretion rate and therefore the shape and depth of the photospheric metal absorption lines. This paper presents an 18-year optical spectroscopic monitoring campaign of five warm (11,000-23,000K) polluted white dwarfs with sinking timescales of days-months, observed using Magellan/MIKE and SALT/HRS to directly test this prediction. At four of the five systems, no statistically significant variability is detected over baselines of 15-18 years corresponding to hundreds to thousands of diffusion timescales, with inferred accretion rates stable to within 15-30% (1$\sigma$) showing remarkably stable accretion on decadal timescales. This implies that either the processes maintaining the accretion of the disrupted planetary material are stable on the same timescales, or that currently uncharacterized photospheric processes act to smooth observable abundance variations on these timescales. The one exception, WD 0106$-$328, shows statistically significant variability in the 4481A Mg II doublet from the ground-based data. Yet no significant equivalent width or abundance changes are seen between two Hubble Space Telescope ultraviolet spectra taken in 2016 and 2025, despite probing a larger set of transitions. This may imply that the ground-based observations witnessed a stochastic excursion from a stable baseline accretion rate, rather than a sustained change in the bulk accretion rate.

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astro-ph.EP 2026-07-01

Mass loss dominates orbits of planets around white dwarfs

by Richard J. Parker (1), Dimitri Veras (2) ((1) University of Sheffield +3 more

White dwarf planets in star clusters: gravitational scattering versus mass-loss effects

Cluster simulations find stellar evolution effects outweigh scattering regardless of density, yielding populations for Roman and JWST.

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White dwarfs are unique laboratories for understanding the formation, evolution and survivability of planetary systems. Post-main sequence mass-loss will change planetary orbital properties and stir up debris discs, leading to the observed pollution of white dwarf atmospheres. However, to date, very few studies have investigated the impact of the stellar birth environment on white dwarf planetary systems. In this paper we simulate the evolution of giant planets around white dwarf progenitors from their formation in a star-forming region until 1Gyr, when the most massive stars ($>$2M$_\odot$) have left the main sequence. Our simulations self-consistently model $N$-body interactions between stars and planets while stars evolve into white dwarfs within the cluster lifetime. We find that although scattering interactions in dense star-forming regions create free-floating planets, and alter the orbital properties of up to 20 per cent of the surviving planets, the effects of mass-loss from the star dominate the dynamics. This behaviour is independent of the stellar density of the birth star-forming region, and largely independent of the initial planet orbital properties. Our simulations produce both captured planets around white dwarfs (potentially similar to WD 0806-661b), and triple systems with white dwarfs and planets (potentially similar to PSR B1620-26(AB)b), and our results yield a population synthesis of giant planets from 1 - 100au that may be relevant to Roman, Gaia and JWST observations.

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astro-ph.GA 2026-07-01

Stars heat when migrating inward in Milky Way galaxies

by Cecilia Steel, Andrew Wetzel +4 more

Hot or Cold? Radial Redistribution of Stars in FIRE Simulations of Milky Way-Mass Galaxies and the Asymmetry of Inward versus Outward Migrators

FIRE simulations find inward migrators gain eccentricity while some stars cool to circular orbits; overall migration is rarely cold.

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Stars can radially redistribute (migrate) within galactic disks. The degree to which this occurs as dynamically `cold' (preserves orbital eccentricity) or `hot' (increases eccentricity) remains debated. Many models presume that radial redistribution occurs primarily via cold torquing, resulting in changes in angular momentum without dynamical heating. We test the net dynamical heating associated with redistribution over stellar lifetimes using the FIRE cosmological zoom-in simulations of 12 Milky Way-mass galaxies. We select star particles today that underwent significant changes in orbital angular momentum, j_phi, since birth. We investigate net changes in their orbital eccentricity, e, and we quantify the `cold-torqued' fraction of star particles with |Delta j_phi/j_phi,birth| > 0.2 that preserved eccentricity (|Delta e| < 0.1) since birth. The direction of radial redistribution is most critical: outward-migrating stars experienced smaller net changes in eccentricity, whereas inward-migrating stars almost always heat since birth. For stars born on near-circular orbits (e_birth < 0.2), the cold-torqued fraction decreases rapidly with age today and is generally < 50% at ages >~2 Gyr. Stars born on moderately eccentric orbits (e_birth ~ 0.4) are the most likely to preserve their birth eccentricity. However, the cold-torqued fraction is higher in earlier-forming and/or dynamically-colder disks. Significantly, we identify a population of stars that dynamically `cooled', decreasing in eccentricity since birth: this is the primary way that stars end up on near-circular orbits today. Overall, a star's migration direction, its e_birth, and its age primarily determine whether it was dynamically heated, cooled, or unchanged. In general, radial redistribution in FIRE is typically not cold between birth and today.

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astro-ph.GA 2026-07-01

Gaia revises Sh2-106 distance to 1.65 kpc and raises outflow energy 6.5 times

by Sergio A. Dzib

Distance to Sh2-106 from Gaia DR3 and its embedded radio population: implications for a candidate explosive outflow

Larger distance aligns the candidate explosive event with Orion BN/KL energetics at an older dynamical age near 3500 years.

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Sh2-106 has recently been proposed as a candidate explosive molecular outflow (EMO), but the physical interpretation of the region depends critically on its distance. Published estimates span a wide range, leading to large uncertainties in the inferred size, energetics, and evolutionary timescale of the system. Using {\it Gaia} DR3 astrometry, we identify a kinematically coherent stellar population associated with Sh2-106 and derive a cluster parallax of $\varpi_{\rm corr}=0.607\pm0.013$\,mas, corresponding to a distance of $1.65\pm0.04$\,kpc. This value is significantly larger than the commonly adopted extinction-break estimate of 1.09\,kpc. At this revised distance, the inferred kinetic energy of the expanding ionized nebula increases by a factor of $\sim6.5$, reaching $E_{\rm exp}\simeq1.3\times10^{48}$\,erg and placing Sh2-106 in the same order-of-magnitude energetic regime as the Orion BN/KL explosive event, although at a substantially older dynamical age ($\sim3500$\,yr). Archived 5.8\,GHz Karl G. Jansky Very Large Array observations reveal ten compact radio sources in the central region, identifying embedded stellar objects that are suitable for future multi-epoch radio astrometry. No unambiguous high-velocity stellar ejecta are detected in {\it Gaia} DR3, although S106\,IR shows a modest peculiar transverse velocity of $\sim5$\,km\,s$^{-1}$ relative to the cluster centroid. The Gaia-based cluster distance, therefore, significantly revises the physical scale and energetics of Sh2-106 and provides the observational framework required to test whether the region represents an older analogue of the Orion BN/KL dynamical disintegration or a distinct explosive phenomenon.

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astro-ph.HE 2026-07-01

Carbon-alpha rate shifts upper black hole mass gap edge by 30 solar masses

by Jeremy Sakstein, Djuna Croon

The location of the upper edge of the pair-instability supernovae black hole mass gap

Simulations identify the 12C(α,γ)16O reaction as the largest source of uncertainty in where pair-instability supernovae cut off black hole f

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Gravitational wave observations are beginning to probe the upper edge of the pair-instability supernova (PISN) black hole mass gap, a key prediction of stellar evolution. In this work, we quantify the sensitivity of this boundary to uncertainties in stellar evolution using a suite of simulations that vary inputs including nuclear reaction rates, mixing processes, and stellar winds. We find that the $^{12}{\rm C}(\alpha,\gamma)^{16}{\rm O}$ reaction rate is the dominant source of uncertainty, shifting the upper edge by $\Delta M\sim30\,{\rm M}_\odot$, with the triple-$\alpha$ rate producing a comparable shift of $\sim25\,{\rm M}_\odot$. Notably, $^{16}{\rm O}+^{16}{\rm O}$ reactions shift the upper edge by $\sim15\,{\rm M}_\odot$ while leaving the lower edge unchanged, implying they can widen or narrow the mass gap. Other processes affect the location at the $\lesssim10\,{\rm M}_\odot$ level. In contrast to the lower edge, we find that the upper edge is robust to variations in spatial and temporal resolution, indicating that it is reliably resolved in current simulations. Our results demonstrate that the upper edge carries substantial theoretical uncertainty and, while comparatively less affected by astrophysical contamination than the lower edge, provides a direct probe of the nuclear processes governing pair instability. We discuss the implications for interpreting high-mass black hole detections in gravitational wave data.

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astro-ph.SR 2026-07-01

CepA disk fragments at 100 au and launches multiple outflows

by H. Beuther, C. Gieser +22 more

The CepA disk-outflow system at <=0.2'' or <=100au resolution

NOEMA imaging shows sub-structures consistent with an edge-on disk plus a second bipolar flow from the central peak.

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Context: Although there has been significant progress, the physical properties and potential fragmentation of accretion disks around high-mass protostars remain poorly constrained. Aims: We characterize at high angular resolution one of the most nearby (~700pc) high-mass accretion disk candidates CepA HW2. Methods: Using the new long baseline array configuration (~1700m) of the Northern Extended Millimeter Array (NOEMA), we study CepA HW2 with a resolution of <=0.2'' or <=100au at 1.3mm in dust continuum and spectral line emission. Results: The mm continuum emission resolves the central disk candidate into several sub-structures. Conducting a Toomre Q stability analysis based on CH_3CN and continuum data, and a comparison to 3D radiation hydrodynamic simulations shows that the data are consistent with an almost edge-on disk where the observed sub-structures may represent fragments within the disk. The CO and SiO spectral line data confirm a second bipolar outflow (in addition to the well-known jet) emanating from the central peak position. This indicates that this central peak should host at least a binary if not even a higher order multiple system. The usually assumed dense gas tracer CH_3CN shows also contributions from the outflows which complicates further kinematic analysis of the disk. Conclusions: The high-resolution outflow-disk data of CepA reveal a multiply fragmented disk that drives several outflows. These observations enforce the picture of high-mass star formation where multiplicity and fragmentation can happen on the smallest spatial scales related to the inner accretion disks.

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astro-ph.SR 2026-07-01

Stellar magnetism sets exoplanet space weather and detection noise

by E. Iş{i}k, A. Valio +11 more

Magnetic activity in cool stars: manifestations and relevance to exoplanets

Activity in cool stars defines planetary environments while creating the main variability that limits observations.

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Understanding stellar magnetic activity is central to exoplanet science in two ways: it sets the dynamic astrospheric boundary condition governing planetary space environments, and it is the primary obstacle to exoplanet detection and characterisation, since magnetically driven variability imprints correlated quasi-periodic signals across detection time series. In cool stars, MHD-dynamo-generated fields emerge at the photosphere as bipolar regions, drive chromospheric and coronal heating, modulate irradiance and wind, and power flares and coronal mass ejections. Spatial scales range from individual flux tubes to global coronal configurations, and temporal scales from minutes to decades and beyond, requiring observational and theoretical tools of correspondingly wide scope. We review observational manifestations and physical models of magnetic activity in stars with outer convective envelopes, addressed to the exoplanet community. We develop the solar-stellar connection through the 'Sun in Time' framework and a sequence of solar analogues serving as evolutionary snapshots of a solar-mass star over several Gyr. We survey photospheric, chromospheric, and coronal activity diagnostics across timescales, together with forward-modelling tools translating surface field distributions into signals at or above the level of exoplanet detection. Empirical rotation-activity relationships and their physical interpretation are examined across all three atmospheric layers. Surface reconstruction techniques are assessed for their diagnostic reach and limitations. The evolution of magnetism in solar-like stars is discussed as context for habitability and as a window to other worlds. We close with an account of how stellar magnetism sculpts the astrospheric environment and affects close-in exoplanets, followed by a synthesis of outstanding issues and an outlook on future prospects.

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astro-ph.GA 2026-07-01

FASHI survey fits HI mass function to single Schechter form

by Chuan-Peng Zhang (NAOC), Ming Zhu +9 more

The FAST All Sky HI Survey DR2: the FASHI Catalog and the HI Mass Function

Parameters are log M* = 9.89, alpha = -1.31; cosmic HI density is 4.71e-4 from 109000 sources.

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The FAST All Sky HI Survey (FASHI) conducted with the Five-hundred-meter Aperture Spherical radio Telescope (FAST) has mapped $\sim 19500\,\mathrm{deg}^2$ of the sky north of DEC $= -14^{\circ}$, detecting $156411$ extragalactic HI sources at $z< 0.09$ with a median sensitivity of $0.57\,\mathrm{mJy}\,\mathrm{beam}^{-1}$ at a velocity resolution of $6.4\,\mathrm{km}\,\mathrm{s}^{-1}$. The survey achieves unprecedented depth and area coverage, significantly improving upon previous single-dish surveys. Through a detailed completeness analysis that accounts for the survey's non-uniform sensitivity and line-width dependence, we construct a robust HI mass function (HIMF) using a completeness-corrected sample of over $109000$ sources. The HIMF is robustly constrained down to $M_{\mathrm{HI}}\sim 10^{6.2}\,M_{\odot}$. When systematic uncertainties are included, the HIMF is well described by a single-Schechter function with a characteristic mass $\log (M_{*} / h_{70}^{-2}M_{\odot}) = 9.89\pm 0.02$, low-mass end slope $\alpha = -1.31\pm 0.02$, and amplitude $\phi_{*} = (6.38\pm 0.49)\times 10^{-3}\,h_{70}^{3}\,\mathrm{Mpc}^{-3}\,\mathrm{dex}^{-1}$. The derived cosmic HI density is $\Omega_{\mathrm{HI}} = (4.71\pm 0.03_{\mathrm{stat}}\pm 0.40_{\mathrm{sys}})\times 10^{-4}\,h_{70}^{-1}$. FASHI provides the most extensive and sensitive HI catalog to date, establishing an important benchmark for studies of gas accretion, galaxy evolution, and large-scale structure in the local universe.

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astro-ph.SR 2026-07-01

SKA needs special signal chain to image the bright

by Divya Oberoi, Devojyoti Kansabanik +7 more

State-of-the-art Observation, Calibration, and Imaging Framework for Solar and Heliospheric Sciences with SKA

Non-standard configurations and high-fidelity spectropolarimetric snapshots are required to capture emission spanning many orders of magnitu

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The Sun is a surprisingly difficult radio source to observe and image, even with the SKA. It is multiple orders brighter than the typical radio sources, which sensitive radio telescopes like SKA are optimized for. So, configuring the signal chain to enable solar observations while maintaining linearity is the very first non-standard requirement to be met. Next, solar radio emission spans an impressive range along every single phase-space parameter that can be used to describe it -- time scales from solar cycles to millisecond; spectral scales from smooth thermal emission to $\sim$100 kHz coherent emission; brightness temperatures from $10^4$ K for gyrosynchrotron emissions to $10^{13}$ K for bright type-III bursts; fractional polarizations from less than 1\% to nearly 100\%; and angular scales extending beyond a degree. Capturing the dynamics in solar radio emission in their full glory requires, on the one hand, that all the data that goes into making an image be acquired over very short temporal and spectral spans and, on the other, also imposes requirements for very high imaging dynamic range with high polarization purity. Extracting the information at the requisite temporal and spectral scales from SKA data will require a spectropolarimetric snapshot capability with high dynamic range and fidelity. Additionally, some of the most interesting insights into solar physics and space weather come from studying solar activity, which remains inherently unpredictable. This chapter discusses the various considerations that need to be addressed to help realize the promise of solar and heliospheric science from SKA.

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astro-ph.SR 2026-07-01

SKA to enable radio measurements of CME magnetic fields

by Devojyoti Kansabanik, Surajit Mondal +14 more

Role of SKA in Advancing Remote Measurements of Magnetic Fields of Solar Coronal Mass Ejections

Wider bandwidth and higher sensitivity remove current limits on remote diagnostics of solar eruption fields.

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Coronal Mass Ejections (CMEs) are large expulsions of magnetized plasma from the Sun into interplanetary space and are the primary drivers of extreme space weather variations. The strength and topology of CME magnetic fields largely determine their impact on Earth. Although visible-light coronagraphs routinely observe CMEs and provide their geometric and kinematic properties, they cannot directly measure CME vector magnetic fields. These fields evolve from initiation through the inner heliosphere due to interactions with other CMEs, coronal structures, and the ambient solar wind, leading to significant structural deformation. Such evolution complicates predictions of the CME magnetic field at Earth. Accurate measurements of CME magnetic fields in the corona and heliosphere are therefore essential for advancing space weather forecasting. Radio observations spanning MHz to GHz frequencies provide a powerful remote-sensing approach for measuring CME magnetic fields from the ground. Recent observations with Square Kilometre Array (SKA) precursors and pathfinder instruments, as well as other new-generation facilities, have demonstrated the potential of these radio techniques for CME magnetic-field diagnostics. At the same time, these studies have highlighted several limitations of current instruments. The higher sensitivity, wider instantaneous bandwidth, and broader frequency coverage of the SKA will open a new observational window, enabling these techniques to be fully exploited for constraining SpWx models and improving predictive accuracy. However, such observations are non-standard and require special consideration in scheduling, calibration, and imaging. Developments achieved with SKA precursors and pathfinders are paving the way for robust CME magnetic-field measurements with the SKA.

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physics.space-ph 2026-07-01

Proxy-driven model forecasts galactic cosmic-ray fluxes over decades

by David Pelosi, Fernando Barão +4 more

A new model for long-term forecasting of Galactic cosmic rays

A one-dimensional transport equation with solar-proxy parameters matches existing data and projects intensities for future mission planning.

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The modulation of galactic cosmic rays, driven by the evolution of the heliospheric magnetic field, strongly influences the intensity of cosmic rays reaching near-Earth space. Characterizing this process is crucial both for advancing our understanding of cosmic-ray transport and for assessing radiation exposure and related hazards in space environments. Here we present a newly developed forecasting framework built on a numerical description of charged particle transport in the heliosphere and its dependence on solar activity, designed for the long-term forecasting of galactic cosmic-ray fluxes. It solves a one-dimensional, spherically symmetric form of the Parker transport equation, including diffusion, solar-wind advection, and adiabatic energy losses. The model has been validated using multi-species flux measurements from space-based experiments: PAMELA, AMS-02, and ACE. Its strategy is based on Hilbert-Huang transform filtering and cross-correlation between delayed solar proxies and effective model parameters. Our charge-sign- and rigidity-dependent parametric description of the diffusion-advection processes yields good overall agreement with the data, as shown by the reconstruction uncertainty. The robustness of this approach is validated across a broad set of multichannel datasets covering different particle species, energy ranges, and phases of solar activity, supporting its applicability to space radiation monitoring and forecasting. Furthermore, when coupled with solar-proxy forecasting models, it enables decadal-scale predictions of galactic cosmic-ray fluxes, thereby supporting long-term planning and radiation-risk assessment for future space missions.

0

astro-ph.SR 2026-07-01

Higher 12C+12C rate boosts heavy elements in supernova ejecta

by L. Roberti, S. Palmerini +11 more

Impact of Sub-2.5 MeV 12C+12CResonances on the Production of Elements from C to Pd in Core-Collapse Supernovae

Extended carbon burning enlarges convective cores and activates the 13C(α,n) source, setting ejecta composition more than explosion details

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We explore the impact of a more efficient 12C+12C reaction on the structure and nucleosynthesis of massive stars. We calculate non-rotating stellar models with initial masses of 15, 16, 18, 20, 22, 25, and 40 Msun and solar metallicity by means of the FRANEC code. Furthermore, we simulate the core-collapse supernova of these models with the thermal bomb technique, using two different approaches to inject the thermal energy into the pre-supernova structure. Our results show that a more efficient 12C+12C rate extends the duration of the central carbon burning phase, developing more massive convective cores and leading to a different and less compact pre-supernova structure with respect to models calculated with a standard 12C+12C rate. These structural differences significantly impact nucleosynthesis. In particular, an increased rate enhances the production of elements heavier than Fe, produced by the s-process nucleosynthesis and driven by the more efficient activation of the 13C($\alpha$,n) neutron source in the early carbon burning shells. We find that the differences in the chemical composition of the core-collapse supernova ejecta are primarily determined by these pre-supernova structural changes, which dominate over the effects of different explosion prescriptions.

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astro-ph.GA 2026-07-01

Neural network unifies six extinction maps into 1.9 billion stars

by Baisong Zhang, Bingqiu Chen +10 more

GSED: The Galactic Stellar Extinction Database

Query service returns corrected E(B-V), Gaia colour excess and A_V from homogenized stellar data

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Reliable extinction correction is essential for nearly all astrophysical studies within the Galaxy. We present the Galactic Stellar Extinction Database (GSED, https://nadc.china-vo.org/data/gsed/), a homogenised database that unifies six representative 3D extinction datasets under a common $E(B-V)$ and parallax-distance baseline. A six-layer multilayer perceptron is designed to correct the systematic differences in both extinction and distance across the heterogeneous input catalogues. Applying the trained models yields a catalogue of over 1.9 billion homogenised entries, which is built into a publicly accessible, real-time query service: a user supplies a coordinate and a search radius, the system retrieves the data, fits the distance--extinction relation, returns $E(B-V)$ together with $E(G_{\rm BP}-G_{\rm RP})$ and $A_V$, and allows the raw catalogue and the fitted curve to be downloaded. By delivering extinction as raw stellar measurements rather than voxelised map products and retaining the capacity to incorporate future datasets, GSED provides a flexible, traceable, and extensible new tool for Galactic extinction correction and dust-structure studies.

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astro-ph.EP 2026-07-01

Stellar spots dominate AU Mic b transmission spectrum

by William C. Waalkes, Peter Gao +11 more

The HST/WFC3 Transmission Spectrum of AU Mic b Part I: An Atmosphere Obscured by Contamination and Systematics

The young planet's near-IR spectrum shows the transit light source effect overwhelming atmospheric signals, with data favoring a scale heigh

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Young sub-Neptune progenitors around M dwarfs offer an excellent opportunity to probe the formation of their abundant, older cousins. At $\sim$20 Myr and only 9.7 pc away, AU Mic b is an ideal candidate for this effort, with its density and observations of escaping hydrogen pointing to a significant primordial atmosphere. Here we present the 0.8-1.6 $\micron$ transmission spectrum of AU Mic b observed with the Wide Field Camera 3 on the Hubble Space Telescope (HST). We find that HST experienced unstable scanning during its visits, resulting in a variable PSF that dramatically affects the orbit-to-orbit baseline of the observations. While we were able to somewhat mitigate this problem through spectral binning, the effects cannot be completely eliminated, limiting the precision of our results. Our data is further impacted by the intense magnetic activity of AU Mic, which introduced significant rotational variability along with spot crossings and the transit light source (TLS) effect into the light curves and spectrum, respectively. Through decomposition of the out-of-transit stellar SED, we are able to constrain AU Mic's photospheric and spot temperatures to 3891$\pm$37 and 3020$\pm$69 K, respectively, with a spot filling factor of $0.33\pm0.05$. Using Bayesian atmospheric retrievals, we show that the spectrum is dominated by the TLS effect with weak atmospheric constraints, with the data preferring a relatively small scale height of $<$185 km to 3$\sigma$. Extrapolation of our retrieved spectra shows that the TLS effect dominates over atmospheric features at optical and infrared wavelengths.

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astro-ph.SR 2026-07-01

High-redshift stars show larger color spreads than local ones

by Yang Chen, Xiaoting Fu +3 more

Bolometric correction for cosmologically redshifted stars with dust: an update to the YBC database

Bolometric corrections with redshift and dust produce non-monotonic colors and bigger dispersions, pointing to tighter parameter estimates w

abstract click to expand

Observations from HST & JWST continue to reveal gravitationally magnified high-redshift star candidates, resulting in increasing demand for accurate stellar bolometric corrections to compare stellar models with observational data. We update YBC stellar bolometric correction database by incorporating bolometric corrections for cosmologically redshifted stars, called zYBC. The bolometric corrections are derived by redshifting stellar spectra from libraries, attenuated by extinction curves for both the dust in the host galaxy and the Milky Way, and followed by convolution with the transmission curves of photometric filters. Our methodology incorporates the effects due to the cosmological K-correction and the dust. Besides the spectral libraries in earlier YBC, we add NLTE-based spectral libraries for O, B stars, which are better suited for hot massive stars, particularly wind-included PoWR and CMFGEN models. The database supports key photometric systems for high-redshift studies, such as HST/WFC3, JWST/NIRCam, and CSST's MSC and MCI, and maintains the flexibility to incorporate additional photometric systems upon request. As examples, we present colors as functions of Teff at various redshifts for several photometric systems, which exhibit non-monotonic behaviors and demonstrate the necessity for a dedicated modelling. In particular, we find that the relations show larger dispersions at high redshift than the zero redshift case. This indicates that the stellar parameters of high redshift stars can be better determined than those of their local counterparts, given their redshifts reliably determined through other methods and their photometric data are of high enough quality for physical parameter determination through spectral-fitting. We also show the difference in the effect brought by the different amount of extinctions. zYBC represents a valuable resource for high-redshift star research.

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astro-ph.GA 2026-07-01

Masers act as cosmic rulers from AU to kpc scales

by Kazi L. J. Rygl, Anna Bartkiewicz +10 more

Cosmic Rulers: Masers as Tools for Probing Structure in the Galaxy and Beyond, from AU to kpc

Their compactness and brightness allow precise mapping of hidden dynamics in dusty regions and distant galaxies.

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Maser emission provides an unique window into astronomical sources across vast spatial scales - from tens to hundreds of astronomical units around protostars and evolved stars up to kiloparsecs in distant galaxies. These natural microwave amplifiers penetrate dust shells in star-forming regions, revealing the dynamics of accretion disks and outflows, trace envelopes and winds of evolved stars, map Galactic structure, while also allowing us to follow the evolution of all these systems. Owing to their compactness and brightness masers provide precise astrometry as cosmic rulers: measuring positions, structures and kinematics in dense regions, not easily accessible at other wavelengths. SKA-Mid will observe hydroxyl, methanol, and formaldehyde masers using bands 2, 5a and 5b, and later methylidyne radical masers in band 4. SKA-Mid's sensitivity and broad frequency coverage will support discoveries of new maser types and allow for simultaneous multi-transition and multi-species maser observations. In addition, bright masers can serve in the science verification of the SKA-Mid array during the deployment phase.

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astro-ph.SR 2026-07-01

Magnetofrictional run reproduces 50-hour flux-rope buildup in AR 12975

by Dinesh Mishra, P. Vemareddy +1 more

Formation and Eruption of Filament Channel in Solar Active Region 12975: Insights from Observations and Simulations of Magnetic Field Evolution

Helicity ratio reaches 0.23 at observed eruption yet torus instability appears only at 0.32 because rope sits beside older fields.

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We studied the magnetic field evolution of active region (AR) 12975 using a time-dependent magnetofrictional (TMF) model. This AR produced two consecutive CMEs associated with M-class flares on March 28, 2022. The AR exhibited a simple bipolar configuration, with new bipolar flux emerging from March 27. These emerging flux regions evolved through shear motions, forming a filament-channel that ultimately erupted on March 28 at 12:00 UT. The simulation, initialized at 12:00 UT on March 26, is driven by electric fields derived from a time-series of photospheric vector-magnetograms. It reproduces the observed coronal evolution, including the gradual development of a sigmoidal, twisted flux rope (FR) over approximately 50 hours. The modeled temporal evolution of magnetic energy and helicity within the computational domain is consistent with the observed injection of both quantities. Furthermore, the ratio of current-carrying to total relative helicity reaches 0.23 at the time of observed eruption, however the torus-unstable regime is attained when the helicity ratio reaches 0.32, approximately 7 hr after the observed eruption. Notably, the FR forms adjacent to pre-existing magnetic fields, and a substantial portion of the coronal structure does not belong to the FR system. Consequently, the derived helicity thresholds vary and deviate from the proposed value of 0.29. While reproducing filament formation with high morphological accuracy, this study underscores the quantitative challenges involved in modeling and evaluating the eruptive behavior of different ARs.

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astro-ph.IM 2026-06-30

SHARP reaches H=24 for YSO studies beyond 5 kpc

by Juan Manuel Alcala', Alessio Caratti o Garatti +6 more

SHARPing accretion and outflows in young stellar objects in star forming regions of the outer Galaxy and beyond

Exposure time calculator confirms signal-to-noise for embedded accretion and outflow observations in outer Galaxy and Magellanic Clouds

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As part of the science book of SHARP, we present here the science case of star-disk interaction of low-mass (\Mstar$\leq$2\Msun) young stellar objects (YSOs), in low-metallicity (Z$<$ 0.2 \Zsun) star forming regions (SFRs) and supermassive star clusters, using the SHARP instrument mounted on the ESO-ELT. Extreme adaptive optics (AOs), with a spatial resolution a factor $\sim$3 better than JWST, as well as sensitive multiplexing capabilities, uniquely offered by SHARP, are essential to efficiently survey the whole area of low-Z SFRs and massive clusters in the outer Milky Way (MW) Galaxy and in the Magellanic Clouds (MCs). Using the SHARP exposure time calculator (ETC) we demonstrate that SHARP can achieve the required signal-to-noise, both for the continuum and emission lines, to investigate accretion and outflows in YSOs in distant (d$>$5\,kpc) SFRs, including those relatively embedded. SHARP will be able to observe very faint YSOs ($H\sim$\,24\,mag), allowing us extending studies to very low-mass YSOs in distant SFRs. The performance of SHARP in terms of sensitivity and spatial resolution in the NIR will provide significant insights into the evolution of protoplanetary disks in low-metallicity and massive environments: studies of accretion, jets/winds and photo-evaporation processes, down to the very low-mass ($\sim$0.2\,\Msun) regime in the MCs, and down to substellar YSOs in SFRs of the outer MW Galaxy (d\,$\lesssim$\,10\,kpc), will be possible. SHARP will also be able to observe jets/outflows in targets that are several magnitudes fainter than those reachable with current instruments, and will facilitate studies in low metallicity environments of wide binaries and multiple systems, with separations of $\sim$1600\,au, at a distance $\sim$50\,kpc scale, and of $\sim$150\,au, in regions of the outer MW Galaxy (d $\sim$10\,kpc).

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astro-ph.SR 2026-06-30

Radio trends point to shared breakout process in stars and dwarfs

by Francesco Cavallaro, Paolo Leto +16 more

Coherent and Incoherent Emission from the Ordered Magnetospheres of Low-Mass Stars, UCDs, and Massive Stars

Luminosity patterns match between massive magnetic stars and ultracool dwarfs, suggesting the same plasma-release mechanism operates despite

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Massive early-type (B/A) stars and ultracool dwarfs (UCDs) represent two distinct regimes in which ordered, large-scale magnetospheres are observed. In rapidly rotating massive stars, incoherent radio emission is explained by the centrifugal breakout (CBO) mechanism: plasma confined within the rigidly rotating magnetosphere accumulates beyond the co-rotation radius, where centrifugal forces trigger breakout events and magnetic reconnection, generating non-thermal electrons that produce incoherent gyro-synchrotron emission. Empirically, the radio luminosity correlates with the power released by CBO events, establishing a clear link between stellar rotation, magnetic confinement, and radio output. In UCDs, persistent non-thermal radio emission exhibits similar luminosity trends to those of massive magnetic stars, despite the absence of strong stellar winds. This similarity suggests that a CBO-like process may also operate in these fully convective, low-mass objects, though the plasma source and acceleration mechanisms remain uncertain. In both classes, coherent electron cyclotron maser emission (ECME), characterized by strong polarization and rotational modulation, is observed, indicating common magnetospheric processes analogous to planetary auroral emission. The Square Kilometre Array (SKA) will be able to deeply observe about 70\% of the sky. We expect to observe $\sim 1000$ UCDs, enabling better statistical analysis of their emission and a test of the CBO hypothesis.

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astro-ph.GA 2026-06-30

B0 stars ionize 40 percent of 1327 Galactic HII regions

by Athanaseus J.T. Ramaila, Mark A. Thompson +8 more

SMGPS: A study of Galactic HII regions with extended morphology

Radio data give photon outputs and radius-density relations governed by local conditions rather than Galactic position.

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We present a study of ionised hydrogen ($\textrm{H}\scriptstyle\mathrm{II}$) regions in the Galactic Plane using data from the SARAO MeerKAT Galactic Plane Survey (SMGPS). The SMPGS is a wide-field, wide-band 1.3 GHz radio continuum survey ($251^\circ \leq l \leq 358^\circ$ and $2^\circ \leq l \leq 61^\circ$ at $\quad |b| \leq 1^\circ.5$) that has enabled us to trace the diffuse emission enveloping recently formed massive stars. Our multifrequency synthesis images reveal faint and extended emission that was previously overlooked by $\textrm{H}\scriptstyle\mathrm{II}$ region surveys. We report the distances and Lyman-photon flux ($N_{\mathrm{Ly}}$) measurements for 1,327 Galactic $\textrm{H}\scriptstyle\mathrm{II}$ regions from which we characterise the spectral types for candidate ionising stars. The spectral types range from B3 to O4. The typical stellar spectral type responsible for ionisation is the B0, which constitutes about $\text{40 %}$ of our catalogue, corresponding to a mean $\log(N_{\mathrm{Ly}}) = 47.5\ \mathrm{s}^{-1}$. Moreover, as a result of the lack of radio recombination line (RRL) velocity measurements for faint $\textrm{H}\scriptstyle\mathrm{II}$ regions, we identify the effective completeness limit at $\log(N_{\mathrm{Ly}}) \approx 46.8\ \mathrm{s}^{-1}$. The multiwavelength approach reveals that the physical radius at 1.3 GHz and in the mid-infrared are well correlated with a slope of $1.15 \pm 0.02$. We find clear power-law relations between $N_{\mathrm{Ly}}$ and physical radius, and an inverse correlation between electron density and radius ($n_{\rm e} \propto R^{-0.73}$). However, no significant correlation is observed between the $N_{\mathrm{Ly}}$ and Galactocentric distance, suggesting that the observed trends are governed primarily by local star-forming environments rather than large-scale Galactic gradients.

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astro-ph.EP 2026-06-30

Reflected light from LTT-9779 b measured at 102 ppm

by F. Borsa

High-resolution detection of reflected light from the exo-Neptune LTT-9779 b

ESPRESSO cross-correlation yields geometric albedo 0.88, matching photometry and indicating a reflective atmosphere.

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While high-resolution spectroscopy is routinely used to probe exoplanetary atmospheres, detecting reflected starlight remains highly challenging due to the extremely low planet-to-star optical flux ratios. We report the detection of reflected light from the ultra-hot exo-Neptune LTT-9779 b using high-resolution spectroscopy with ESPRESSO in its 4UT mode. By combining multiple epochs and applying a cross-correlation analysis with a theoretical reflection kernel, we were able to identify a faint signal matching the expected morphological and kinematic profile of the planetary reflection. This signature, whose presence has been detected at a signal-to-noise ratio of $\sim$5.4, exhibits a radial velocity semi-amplitude consistent with the expected orbital motion. We measured the planet-to-star flux ratio from the ratio of the equivalent widths of the planetary and stellar cross-correlation functions, finding $F_{\mathrm{p}}/F_\star = 102^{+29}_{-30}$ ppm for the ESPRESSO 380--770 nm wavelength range. Assuming a Lambertian phase function, this corresponds to a geometric albedo of $A_{\mathrm{g}} = 0.88 \pm 0.25$. The inferred albedo is consistent with previous space-based photometric measurements, suggesting a highly reflective atmosphere potentially dominated by scattering processes or high-altitude clouds. While we show that reflectivity is enhanced towards blue wavelengths, a detailed spectroscopic characterization of the planetary atmosphere from the reflected-light signal remains out of reach. This result highlights the scientific potential of future high-resolution spectrographs on extremely large telescopes, paving the way for systematic reflected-light detections across a broader exoplanet population, including cooler and smaller planets.

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astro-ph.SR 2026-06-30

IceCube recovers SASI frequency to sub-percent precision

by Dwaipayan Mukherjee (Tata Inst.), Mohamed Rameez (Tata Inst.) +1 more

Parameterizing the Standing Accretion Shock Instability for Inference with Galactic Supernova Neutrino Signals at IceCube

Parametrization of neutrino rate modulation extracts timing, amplitude and duration of the instability at few-to-ten-percent level for Galac

abstract click to expand

Simulations of core-collapse supernovae have revealed an epoch of hydrodynamic instability in which the matter of the collapsing star undergoes quasi-periodic oscillations, known as the standing accretion shock instability (SASI). Neutrinos produced in the core of the star travel through this oscillating matter, and information about this epoch is encoded in their high-statistics event rate observable at neutrino observatories. We propose a parametrization of the SASI-modulation to study its broad features, enabling statistical inference of SASI parameters. For the benchmark Galactic supernovae considered, we show that IceCube can identify this epoch of instability and reconstruct its parameters with precision at the sub-percent level for the SASI frequency, percent level for the peak time, and a few to ten percent level for the amplitude and duration.

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astro-ph.GA 2026-06-30

Ages in wrinkles trace past spiral arm passages

by Amy Smock (1), Kathryne J. Daniel (1) +7 more

Wrinkles in Time. II. Stellar Age Trends in Kinematic Signatures from Transient Spiral Structure

Simulations show young stars from circular orbits can fill high-action regions usually occupied by older stars

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Spiral arms in the disks of galaxies like the Milky Way can generate kinematic signatures, which appear as ridges or wrinkles in action space. Such signatures have proven difficult to disentangle using kinematic measures alone. In this study, we investigate how including stellar age as an additional dimension for analysis may provide a novel insight into the physical characteristics, timescales, and nature of the progenitors of such perturbations, where these novel insights could contribute to our understanding of the history of spiral arms in the Milky Way. We used a suite of tracer particle simulations that modeled a variety of prescriptions for spiral arms to characterize observable trends. The Lindblad resonances of nonwinding spirals produce signature overdensities, or wrinkles, in a kinematic space that is typically associated with older stellar populations (high radial action). We find that these wrinkles are preferentially populated with stars that were initially in nearly circular orbits, kinematics that is generally correlated with younger stellar ages. It follows that the stellar age distribution of wrinkle populations could serve to place constraints on the past passage of a transient spiral pattern in the solar neighborhood. For example, our simulations suggest that a physically motivated spiral pattern could significantly populate a wrinkle with zero-age stars in orbits typically occupied by stars much older than the Sun.

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astro-ph.GA 2026-06-30

Pixel analysis lifts Pop III recovery to 90% in JWST mocks

by Patricia Iglesias-Navarro, Thomas Harvey +12 more

A Pixel-by-Pixel Path to Population III Discovery with JWST

Spatially resolved comparisons separate primordial stars from host contamination more effectively than whole-galaxy measurements.

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The identification of the first generation of metal-free stars, known as Population III (Pop~III), remains a primary goal of modern observational astronomy. While JWST has discovered an abundance of UV-bright galaxies at $z > 10$, distinguishing primordial stellar populations from early metal-enriched systems is a significant challenge. We present an end-to-end framework that combines physically motivated forward modelling from Yggdrasil primordial models with simulation-based inference (SBI) to test Pop~III detectability in JWST-like observations, from isolated sources to realistic overlap with enriched (Pop~II) hosts. Our analysis spans several Pop~III initial mass function (IMF) assumptions, nebular configurations, and Lyman-$\alpha$ transmission scenarios, while mocking the noise properties and filter coverage of the JWST Advanced Deep Extragalactic Survey (JADES). We find that unresolved or integrated analyses are strongly limited by host-galaxy contamination, whereas spatially resolved, pixel-based model comparison substantially improves recoverability. In our resolved experiments, detectability is highest for young and massive Pop~III clumps in nearly-quenched hosts at larger projected separations from their centres, reaching $\sim 90\%$ recovery in favourable configurations, while older and centrally embedded clumps are rarely recovered. Applying the framework to a literature candidate yields spatially differentiated behaviour: a compact blue companion is preferentially described by Pop~III-like models, while the host is better explained by fiducial Pop~I/II models. Our pipeline provides practical criteria for future searches and motivates imaging-first, spectroscopy-assisted strategies for identifying primordial stellar populations in JWST data.

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astro-ph.SR 2026-06-30

Ancient records of Theta Eridani brightness match a real binary transient

by Idel Waisberg, Boaz Katz

The forgotten bright star: Theta Eridani as a millenary stellar transient observed by Hipparchus, Ptolemy and al-Sufi

Orbital solution shows prior eccentricity near 0.6 drove a millenary common-envelope phase with Delta V of 2.7

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Theta Eridani is a V=2.9 star that was nonetheless reported as one of the thirteen brightest stars in the night sky by both Ptolemy in his Almagest (137 AD) and by al-Sufi in his The Book of Fixed Stars (964 AD), in addition to being previously referred by Hipparchus (129 BC) as a particularly bright star. The discrepancy between its historical and modern visual magnitude $\Delta V \sim 2.7$ is the highest among the $\sim 1000$ stars in the Almagest. Theta Eridani is actually a triple star system, and here we combine interferometric data from VLTI/PIONIER and VLTI/GRAVITY, spectroscopic data from ESPaDOns and FEROS, and photometric data from TESS in order to solve for the orbital parameters, masses and radii of the close inner binary Theta Eridani Aa+Ab. We find that it is a tight eccentric binary ($a=0.083 \text{ au}$, $e=0.105$) of intermediate-mass stars ($M_{Aa}\simeq 2.3 M_{\odot}$, $M_{Ab}\simeq 2.2 M_{\odot}$) that are extended to $\sim 80\%$ of their Roche lobe radii ($R_{Aa}\simeq 4.3 R_{\odot}, R_{Ab} \simeq 4.0 R_{\odot}$), resulting in prominent ellipsoidal oscillations in the lightcurve. We also find that the primary is in a very special phase of its evolution in which it has just finished core hydrogen burning. The remarkable combination of orbital and stellar parameters hints that the historical brightening of Theta Eridani was due to a millenary transient phase powered by orbital energy extraction during a long-lived ``common envelope'' stage triggered by eccentric Roche lobe overflow in a previously more eccentric binary ($e\simeq0.6$). This strengthens the case that the apparent brightening was real and not due to an error by three different ancient observers, as has been commonly claimed in the past.

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astro-ph.SR 2026-06-30

Review outlines methods to detect star-planet interactions amid stellar noise

by P. Figueira, H. Korhonen +9 more

Star-Planet Interactions: Observational Techniques and Methods

Radial velocities, photometry, spectral lines and radio data are examined for their ability to isolate planetary effects from stellar activi

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This chapter summarizes the techniques and methods used to study star-planet interaction (SPI) from the observational point of view. SPI can produce a wide range of observational signatures, from localized stellar activity enhancements to changes in planetary atmospheric escape and transmission spectra. This chapter reviews the main observational techniques used to detect and characterize SPI, emphasizing the methodological challenges involved in separating planet-induced signals from intrinsic stellar variability. We discuss radial-velocity diagnostics, including cross-correlation, template matching, line-by-line methods, and activity indicators, highlighting their sensitivity to line-profile distortions and chromatic variability. We then review precision photometry as a tool to search for orbit-locked variability, flare modulation, and active-region occultations during planetary transits. Chromospheric diagnostics, including Ca II, Halpha, He I, and Na II lines, are presented as tracers of magnetic variability at different atmospheric heights and as potential probes of intermittent SPI signatures. We also discuss transmission spectroscopy as a complementary approach, since planetary atmospheric tracers such as H I Lyalpha, Balmer lines, C II, and He I can encode information about the stellar high-energy environment, stellar wind, and magnetic coupling. In addition, radio observations provide a promising avenue to probe magnetic SPI directly through coherent emission mechanisms. Finally, we examine time-series analysis techniques commonly employed in SPI searches, including generalized Lomb-Scargle periodograms, rolling periodograms, harmonic analyses, and bootstrap-based significance estimation. (abridged)

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astro-ph.SR 2026-06-30

L2 brown dwarf found orbiting A0V star HIP 17453

by Marah Brinjikji, Adam J. Smith +27 more

The Companions to B and A Stars Snapshot (C-BASS) Survey: I. Discovery of a Young Brown Dwarf Companion to HIP 17453

The 53 Jupiter-mass object at 81 pc has mass ratio 0.024 and is suitable for benchmark atmospheric studies.

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We report the detection of a new brown dwarf companion to HIP 17453 A, a chemically peculiar A0V star located at a distance of 81 pc. HIP 17453 A was observed with high-resolution adaptive optics imaging using the Near-Infrared Camera 2 on the Keck II telescope as part of the Companions to B and A Stars Snapshot (C-BASS) survey over a ten-year baseline, revealing the presence of a companion with proper motion consistent with the primary. We estimate the age of the HIP 17453 system as 280 $\pm$ 125 Myr, and with follow-up intermediate resolution (R~1800) spectroscopic observations with the Gemini Near Infra-Red Spectrograph (GNIRS) on the Gemini-North telescope, we found the spectrum of HIP 17453 B to be consistent with a spectral type of L2 $\pm$ 1. Through interpolation of Sonora Diamondback evolutionary models, we calculate an effective temperature of $1953^{+84}_{-78}$ K and mass of $53^{+10}_{-8}$ $M_{Jup}$ for HIP 17453 B, which corresponds to a mass ratio of $q = 0.024 \pm 0.004$ for the HIP 17453 system. With its intermediate mass and young age, HIP 17453 B joins a small set of benchmark brown dwarf companions around early-type stars that are suitable for follow-up atmospheric and evolutionary studies.

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astro-ph.EP 2026-06-30

Giant planet hosts enriched in C O S Fe Ni

by E. Costa-Almeida, L. Ghezzi +3 more

Chemical Abundances of the Bioessential Elements C, O and S, and the Refractory Elements Fe and Ni, in Solar-type Exoplanet-hosting Stars from HARPS North and South

290-star sample finds higher abundances for all five elements when planets exceed 4 Earth radii in size.

abstract click to expand

We determined atmospheric and evolutionary parameters, along with chemical abundances of C, O, S, Fe, and Ni for 290 solar-type exoplanet hosting stars using high-resolution HARPS-North and HARPS-South spectra, and radii for 373 exoplanets using literature transit depths. We find that stars hosting giant exoplanets (R$_{\text{pl}}>4\ \text{R}_{\oplus}$) show enhanced [X/H] abundances compared to small exoplanet hosts for all elements analyzed. When considering only exoplanets with $P_{\text{orb}}\leq30$ days, there is a statistically significant anti-correlation between host star [Fe/H] and $P_{\text{orb}}$. However, [Fe/H] does not continue to decline as the orbital period increases, but rather rises again for exoplanets with larger orbital periods. Stars hosting only small exoplanets or hosting at least one sub-Saturn show significant differences between the populations of hot and warm exoplanets for all elements. In contrast, stars hosting at least one Jupiter-sized planet show no abundance differences. The host star C/O ratios obtained vary from 0.17 to 0.95, with giant exoplanet hosts exhibiting the lowest median C/O ratios (0.43$^{+0.02}_{-0.03}$), while the 3 -- 4 R$_\oplus$ sub-Neptune hosts in our sample exhibit the highest median C/O ratios (0.55$^{+0.05}_{-0.01}$). Our sample has 199 exoplanets with estimated masses and we find correlations between host star [O/H] and [S/H] and $\log(M_{\text{pl}}/\text{M}_\oplus)$. When segregating the sample into hot and warm exoplanet hosts, these trends are only found for warm exoplanets. Dividing the sample between low- (91 exoplanets) and high-[$\alpha$/Fe] (20 exoplanets) stars, there are trends between host star [O/H], [S/H], [Fe/H] and [Ni/H] and $\log(M_{\text{pl}}/\text{M}_\oplus)$ only for the low-[$\alpha$/Fe] sample.

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astro-ph.GA 2026-06-30

Little Red Dots host engines below 10^5 solar masses

by Rohan P. Naidu, Jorryt Matthee +21 more

Little Red Dots as Intermediate Mass, Super-Eddington Engines: Insights from Type IIn Supernovae and The 1837-1856 Great Eruption of η Carinae

Escape-velocity limits and parallels to stellar eruptions imply super-Eddington intermediate-mass objects rather than overmassive black hole

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JWST's Little Red Dots (LRDs) display a unique constellation of features that do not occur simultaneously in any other class of galaxies or AGN. Here we observe that many of these features find parallels in the 19th century Great Eruption (GE) of $\eta$ Carinae and a sub-class of supernovae (Type IIn). Drawing on these stellar phenomena -- outflows trapped by dense circumstellar gas envelopes -- we sketch a possible scenario for LRDs. Outflows from the central engine produce an enshrouding envelope of gas that may be thought of as a slow wind. This dense wind and its enormous extent produce an opacity so high that a pseudo-photosphere forms within the wind, obscuring the central engine and manifesting as a blackbody-like continuum. Radiation from the buried engine powers the system. The engine may also launch fast winds that crash into the existing envelope to generate shocks. Lines form within the wind above the photosphere -- electron scattering and absorption in the clumpy (ionized + neutral) medium account for broad wings and P-Cygni cores. A key implication is that inferences of ``overmassive black holes" may be interpreting this wind-like physics as a virial broad-line region. We propose an escape velocity argument to constrain the mass of the engine, which yields $M<10^{5} M_\odot$ for the typical LRD. The lack of variability and low surface gravity of the photosphere provide further support for intermediate mass ($M\approx10^{3-6} M_\odot$), but very luminous super-Eddington ($L_{\rm{bol}}/L_{\rm{edd}}\gtrsim5$) systems harboring a supermassive star or intermediate mass black hole. Paralleling the evolution of IIn SNe, dust production in the envelope may mark the beginnings of classical AGN. This paper explores a possible self-consistent explanation for the entire life-cycle of LRDs, from their enshrouding in dense gas to their fates as seeds of massive black holes.

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astro-ph.HE 2026-06-30

Chandra measures G292.0+1.8 expansion at 0.016% per year

by Maria Aslanidou, Manan Agarwal +1 more

Expansion rate of the young, oxygen-rich supernova remnant G292.0+1.8

Rate implies remnant age near 2500 years for uniform surroundings and slower motion for heavier elements.

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Core-collapse supernova remnants (CCSNRs) are ideal targets for studying ejecta--interstellar-medium interactions, shock dynamics, and explosion characteristics. G292.0+1.8 is a classic CCSNR featuring oxygen-rich ejecta, circumstellar material, a rapidly moving pulsar, and a pulsar wind nebula (PWN). We examine its expansion rate using deep Chandra ACIS-I observations over two nearly independent $\sim$10 yr baselines (2006--2016). After applying astrometric corrections based on Gaia DR3 sources, we extracted radial profiles in 19 sectors around the forward shock. The weighted-mean expansion rate is $0.016\% \pm 0.001\%\,\mathrm{yr^{-1}}$ in the broadband, implying an expansion age of ${\sim}2500$ yr for a uniform ambient medium, consistent with previous estimates of 2000--3700 yr. For a $1/r^2$ circumstellar density profile (Wolf-Rayet progenitor wind), the inferred age is ${\sim}4100$ yr. Narrow-band analysis of $\alpha$ elements (O-Ne, Mg, Si-S) shows that lighter elements follow the broadband behaviour, while heavier elements expand more slowly, consistent with their origin in deeper stellar layers. We discuss the pronounced azimuthal asymmetry of the expansion, the apparent paradox that some sectors expand (with $\sim$2500 km/s) preferentially in the direction of the neutron-star kick, and the role of reflected shocks from the reverse-shock--PWN interaction.

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astro-ph.SR 2026-06-30

Rotation boosts wave mixing in red giants over 100 times

by Simon Blouin, Paul R. Woodward +3 more

Wave-Driven Mixing Enhanced by Rotation in Red Giant Branch Stars

3D simulations show internal waves carry material far more efficiently when stars spin, matching observed surface chemistry.

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Stars like our Sun expand as they exhaust their core hydrogen fuel, becoming red giants that eventually reach sizes up to 100 times their original radius. These giants have long presented a puzzle: they show systematic changes in their surface chemical composition that can only be explained by the transport of material from their nuclear-burning interior to their surface. The challenge is that this transport must somehow cross a stable layer that acts as a barrier between the star's outer convective envelope and its nuclear-burning interior. The convective motions in the envelope create internal waves that propagate through this barrier layer, but on their own these waves produce very little material transport. Here we show through high-resolution three-dimensional hydrodynamical simulations that stellar rotation dramatically amplifies how effectively these waves can mix material across this barrier. We find that the mixing rates can exceed those in non-rotating stars by over 100 times, increasing with faster rotation rates. This enhanced mixing provides a natural explanation for the observed chemical signatures in typical red giants. The amplification of wave-driven mixing by rotation may have implications beyond red giants to other types of stars.

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astro-ph.SR 2026-06-30

Raman lines show layered neutral gas in RR Tel

by Jaejin Shin, Seok-Jun Chang +2 more

High-Resolution Spectroscopy of Raman-scattered He II Lines in the Symbiotic Nova RR Telescopii

Different velocities and lower conversion efficiencies after 20 years indicate the H I region has varying depths and changing geometry.

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Raman-scattered emission features in symbiotic stars provide a powerful diagnostic of mass-loss and transfer processes, as they uniquely probe both ionized and neutral regions within interacting binaries. When resolved with high-resolution spectroscopy, these features encode detailed information on the physical properties of the neutral hydrogen medium. In this work, we present high-resolution spectroscopic observations of the symbiotic nova RR Telescopii obtained with FEROS in 2004 and GHOST in 2024, providing a $\sim$ 20 yr baseline. We report the clear detection of all three Raman-scattered He II lines at 6545 {\AA}, 4851 {\AA}, and 4332 {\AA}, and constrain the distribution and kinematics of H I through line profile analysis. The three Raman lines exhibit distinct relative velocities, indicating that they trace different depths within the H I region. The Raman conversion efficiencies of the three Raman He II lines in 2024 are significantly lower than those in 2004, indicating substantial changes in the physical properties of the neutral hydrogen region. In addition, radiative transfer modeling implies a larger covering factor (opening angle) of the neutral region in 2004 than in 2024. These results indicate that the neutral hydrogen region cannot be characterized by a single H I column density, emphasizing the need for advanced radiative transfer modeling that accounts for the complex kinematics and geometry of the H I region. Overall, these results establish Raman-scattered He II lines as a powerful tool for spectroscopic tomography, allowing for direct constraints on the structure and kinematics of neutral hydrogen in symbiotic binaries.

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astro-ph.SR 2026-06-30

SN 2019vxm peaks at -20.01 mag with slow Type IIn evolution

by Y.-Z. Cai, A. Pastorello +39 more

SN 2019vxm: A luminous and long-lived Type IIn supernova with early flash-ionisation features

Early flash-ionization lines set a lower limit of 0.01 solar masses per year on the progenitor mass-loss rate.

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We present the photometric and spectroscopic analysis of the luminous and long-lasting Type IIn supernova (SN) 2019vxm. The SN reaches a peak V-band absolute magnitude of MV = -20.01 +/- 0.13 mag in 35.0 days, and displays slow evolution in both the light curves and spectra, resembling that of long-lived SNe IIn. A mid-infrared (MIR) excess is detected starting from seven months after maximum brightness, suggesting a few 10^-3 solar masses of dust are newly formed at >= 210 days (and up to 0.01 solar masses at +4.5 yr). The spectra are dominated by a blue continuum at early stages, with narrow, symmetric Balmer lines and flash-ionisation emission lines of C III, N III, and He II. Comparing our flash-ionised spectrum with early interacting SN spectral models, we estimate a lower limit for the mass-loss rate of the progenitor of >= 0.01 solar masses per year. A weak P Cygni absorption feature is detected in the H-beta profile of the high-resolution Echelle spectrum at +19.7 d, suggesting the presence of slow-moving (60 +/- 10 km/s), unshocked circumstellar material (CSM) arising from the pre-SN wind of the progenitor. The H-alpha and H-beta profiles gradually evolve and become broader and asymmetric, showing a progressively increasing blueshift, with a clear flux deficit in the red wings of the broad velocity component after +102 days. Our observed bolometric light curve before about 100 days can be well fitted by a power-law function (L(t) = 2 x 10^44 (t/day)^-0.49 erg/s), which is very similar to SN 2010jl.

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astro-ph.IM 2026-06-30

Nautilus time-series data can map starspots to calibrate exoplanet spectra

by Adina D. Feinstein, Jeff Valenti +10 more

Mapping Stellar Heterogeneities with the Nautilus Space Observatory

Two-generation program links spot-crossing events to heterogeneity properties so contamination becomes a known input rather than an error so

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Stellar photospheric heterogeneities, such as starspots and faculae, are a fundamental limitation for exoplanet transmission spectroscopy. Inhomogeneous surfaces can imprint wavelength-dependent signals during transits that may mimic or mask atmospheric absorption features, especially for planets orbiting cool low-mass stars. Recent work has shown that the information content of transmission spectroscopy observations can be sufficient to correct for stellar contamination, but only if stellar photosphere and active-region models have adequate fidelity. This requires empirical benchmarking with observations that validate next-generation stellar models and identify which spectral diagnostics best encode heterogeneity properties as a function of spectral type, activity level, and time. We propose a two-generation Nautilus program that leverages the scalable architecture of the observatory concept. Generation 1 would use broad-wavelength time-series observations of transiting exoplanet systems to connect starspot-crossing events and out-of-transit variability to localized and disk-integrated heterogeneity properties. Generation 2 would use the optimized spectral diagnostics identified in Generation 1 to conduct slitless spectroscopic monitoring of large samples of GKM stars on different timescales. Generation 2 instrumentation would include activity tracers of both the photosphere and chromosphere. This program would provide the benchmark data and population-level framework needed to turn stellar contamination into a calibrated input for exoplanet atmospheric retrievals.

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astro-ph.HE 2026-06-30

SKAO will enable population studies of wind binaries

by B. Marcote, P. Benaglia +9 more

Enabling population studies on wind-driven Galactic binary systems

Better sensitivity and resolution will let radio telescopes detect weak emissions and resolve sub-au shocks across many Galactic systems.

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Galactic binaries driven by stellar wind shocks, such as colliding wind binaries (CWBs) and gamma-ray binaries (gBs), harbor one of the most efficient particle acceleration engines known in the Universe. Despite their potential, these sources remain relatively unexplored, particularly in the domains of low radio frequencies and very high resolution. As a result, we lack comprehensive population studies and well-characterized individual systems. Only a few of these binaries, such as the iconic gB PSR B1259$-$63 or the massive CWB WR 140, have been studied in enough detail to probe their wind dynamics and shock physics. Current observations lack the sensitivity to detect weak non-thermal synchrotron emission from low-energy particle populations and the angular resolution to resolve shock structures on sub-au scales. The Square Kilometre Array Observatory (SKAO) will mark a significant improvement in both sensitivity and resolution with its SKA-low and SKA-mid telescopes, solving these challenges. This will enable systematic studies of the winds and shock interactions in these binary systems. Additionally, SKA-VLBI will facilitate the observation of changes in shock geometry at different orbital phases, linking particle acceleration processes to the binary's orbital characteristics and stellar wind properties. SKAO will pave the way for comprehensive population studies of these energetic binary systems.

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astro-ph.SR 2026-06-30

New stability rule allows stable mass transfer at higher mass ratios

by M. Echeveste, G. J. Escobar +13 more

The role of mass transfer efficiency in stability criteria: Implementation in SEVN and a test on blue stragglers and binary compact objects

Simulations with the updated criterion produce more blue stragglers in wider orbits and more neutron-star binaries via stable channels.

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Context: The stability of mass transfer through Roche-lobe overflow plays a key role in shaping the outcome of binary interactions. However, the criterion for mass transfer stability remains one of the main open questions in the theory of binary evolution. Aims: We develop a mass transfer stability prescription that accounts for mass and angular momentum loss, and implement it in the population synthesis code SEVN. We assess its impact relative to the standard formalism used in SEVN, using blue stragglers and binary compact objects as illustrative cases. Methods: We derive an expression for the response of the Roche-lobe radius to mass loss in the general case where the mass and angular momentum of the system are not conserved. On the basis of this formulation, we construct a new mass transfer stability criterion that modifies the standard approach only through the Roche-lobe response term. Results: Population synthesis simulations with SEVN show that the new criterion allows stable mass transfer in binaries with higher donor-to-accretor mass ratios, leading to an overall increase in the predicted number of blue stragglers and promoting their formation in wider orbits. This contributes to reconciling the differences between theory and observations. For binary compact objects, the impact of the new stability criterion varies across system types, with the strongest effects occurring in binaries containing at least one neutron star. In particular, for low mass transfer efficiency, the new criterion enhances the contribution of channels involving stable mass transfer and leads to a larger number of systems, including gravitational wave progenitors. Conclusion: The inclusion of a new, simple, yet more consistent prescription for mass transfer stability has proven that refining this criterion can significantly improve our understanding of the formation channels of specific stellar populations.

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astro-ph.SR 2026-06-30

Polar spicules show Alfvénic fluctuations matching turbulence

by Edris Tajfirouze, Christopher H. K. Chen +2 more

Spatially Coherent and Intermittent Alfv\'enic Fluctuations in Solar Polar Spicules

Power spectra scale as k_perp^{-1.43} and kurtosis rises at small scales, consistent with a developing cascade that may transport energy to

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Alfv\'enic fluctuations are considered a key mechanism for transporting energy from the lower solar atmosphere into the corona, with spicules acting as dynamic conduits for this transfer. We investigate transverse and Doppler velocity fluctuations in quiet-Sun polar spicules observed in the Si IV 1394\,\AA\ line by the Interface Region Imaging Spectrograph. Fourier analysis in time and space is used to characterize power across frequency and spatial scales. The temporal power spectra show broadband fluctuations with enhanced power in the 3--7~mHz range and a peak near 4--6~mHz. Spatial Fourier analysis of Doppler velocities reveals a perpendicular power spectrum scaling as $\sim k_{\perp}^{-1.43}$, slightly shallower than the canonical $-5/3$ and $-3/2$ slopes of strong MHD turbulence, but consistent with reflection-driven turbulence simulations. Velocity increment PDFs show non-Gaussian behavior, with kurtosis increasing toward smaller scales, consistent with intermittency. Spatial coherence analysis using cross-correlation and spectral diagnostics indicates an outer scale of a few hundred to about a thousand kilometres, with cross-correlation yielding smaller values. These results provide observational evidence that polar spicules host multiscale Alfv\'enic fluctuations consistent with a developing turbulent cascade and intermittency, suggesting a role in energy transport into the solar corona.

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astro-ph.SR 2026-06-30

FUV irradiation speeds accretion loss in Orion discs

by Rossella Anania, Andrew J. Winter +9 more

Far-ultraviolet flux distribution in Orion and its relation to stellar accretion

Ha detection fraction falls faster in high-flux regions, matching external photoevaporation models.

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Orion is the closest region hosting active star formation and young OBA stars. Computing far-ultraviolet (FUV) fluxes at its stars is essential to connect stellar and protoplanetary disc properties to the environment. We (1) accurately estimated the FUV flux at a large sample of stars in Orion by statistically accounting for the uncertainty in parallax measurements, and (2) investigated the relation between stellar accretion and external FUV flux by comparing observations and disc evolution models. We selected a large stellar population in Orion, assigned sub-cluster memberships and used 2D dimensional sub-cluster geometry to infer 3D separations from OBA stars and compute the FUV flux at stellar positions. We studied the accretion luminosities Lacc inferred from Ha emission in Gaia XP spectra of Orion sources and determined their detection fraction as a function of age and FUV flux. We compared the results with population synthesis models of viscous discs experiencing external photoevaporation. We provided a publicly available table of FUV fluxes at ~8600 stars in Orion. Most of the stellar population is weakly irradiated <10^{2} G0, ~35% is intermediately irradiated 10^{2}-10^{4} G0, and ~5% has FUV fluxes >10^{4} G0. Gaia-based Lacc decreases with age, and Ha detection fraction declines more rapidly in regions with strong FUV fluxes than in regions exposed to weaker FUV fluxes, broadly consistent with the model. This may suggest that external photoevaporation efficiently depletes strongly FUV-irradiated accretion discs, but it is not sufficient to reliably confirm this conclusion. The provided tools for computing FUV fluxes at Orion stars will be essential for future observations aimed at assessing the role of external photoevaporation on discs. We encourage measurements of stellar and disc properties in Orion, covering FUV fluxes 1-10^5 G0.

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astro-ph.SR 2026-06-30

Phase curve measures brown dwarf heat transport below 10%

by Daphne Broski-Laing, Yifan Zhou +11 more

Asymmetric nightside CO2 features, inefficient heat transport, and precise evolutionary constraints: Spectroscopic phase curves reveal the past and present of a white dwarf-brown dwarf binary

JWST spectroscopy of ZTFJ0038 separates components to show inefficient redistribution, CO2 nightside asymmetry, and 7.5-8.8 Gyr age.

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We present the first JWST phase curve of a white dwarf-brown dwarf binary, a NIRSpec PRISM observation of ZTFJ0038+2030. Short-period white dwarf-brown dwarf binaries provide unique laboratories to probe substellar atmospheres. Tidal locking drives hot Jupiter-like atmospheric dynamics in the brown dwarf. The system's formation history offers a window into planetary systems around post-main-sequence stars. We obtain a full-orbit phase curve of ZTF0038, including a total eclipse of the white dwarf, which enables us to separate the two components' emission throughout the entire orbit, and we model the brown dwarf's phase-resolved emission spectra using substellar atmosphere forward models and atmospheric retrievals. The PRISM spectrum covers ~80% of the brown dwarf's bolometric emission, enabling a nearly model-independent energy balance calculation, which yields a day-to-nightside heat transport efficiency of <10%. Inefficient heat redistribution is further supported by the phase curve shape and the nightside spectrum closely resembling non-irradiated mid-to-late T dwarfs. The spectroscopic phase curves reveal a stark nightside asymmetry associated with a strong CO2 absorption feature at 4.2 um, while the retrieved abundances indicate a longitudinally homogeneous distribution of CO2 as well as all other key species detected in the atmosphere. The precise internal luminosity measurement of the brown dwarf informs both the age of the WD-BD system (7.5-8.8 Gyr) and indicates a low common-envelope ejection efficiency. These data illustrate the exquisite opportunity to probe the three-dimensional processes of substellar atmospheres, connect substellar and exoplanet atmospheres, and probe the evolution of post-main-sequence planetary systems using WD-BDs.

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astro-ph.SR 2026-06-30

Sausage modes stand while fluting modes rise in solar pores

by Shahin Jafarzadeh, David B. Jess +35 more

Multi-height Identification of Sausage and Fluting Eigenmodes in a Solar Pore

Eight-line observations show the dominant mode keeps zero phase difference while the m=2 mode gains 50 degrees of phase over 500 km.

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Magnetic pores are compact, strongly magnetised waveguides in the lower solar atmosphere and therefore provide favourable conditions for identifying magnetohydrodynamic (MHD) wave modes. Earlier seeing-free observations revealed concurrent sausage, kink, and fluting modes in photospheric pores, but only at a single sampled layer. In this Letter, we exploit the dense spectral sampling of the near-ultraviolet 327-329 nm window observed by the Sunrise-III UV Spectropolarimeter and Imager (SUSI) to investigate how pore wave modes behave across multiple photospheric and low-chromospheric heights spanning roughly 500 km. We analyse ~75 min of a Sunrise-III/SUSI time series containing a small solar pore. From eight selected spectral lines sampling different estimated formation heights, we identify the pore boundary at each line and time step and apply proper orthogonal decomposition (POD) to the boundary oscillations. In all eight lines, the first POD mode is consistently identified as an axisymmetric sausage mode, with dominant power at ~1-2 mHz, and carries the dominant normalised eigenvalue fraction, typically about 66-86%, while the second mode is a fluting mode with azimuthal wave number m = 2, dominant at ~2-3.5 mHz, and contributes about 4-10%. Cross-line wavelet phase analysis of the temporal coefficients shows that the sausage mode remains close to zero phase difference across the sampled heights, consistent with standing or near-standing behaviour, whereas the fluting mode displays a modest but systematic increase in phase with height, reaching about 50 degrees, indicative of an upward-propagating component. These observations provide the first multi-height identification and phase characterisation of sausage and fluting modes inferred from pore-boundary oscillations.

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astro-ph.SR 2026-06-30

MHD simulation matches observed heights of flare non-thermal sources

by Keitarou Matsumoto, Satoshi Inoue +6 more

Non-thermal Sources from Stereoscopic Hard X-ray and Earth-based Microwave Observations in a Data-Constrained Magnetohydrodynamic Simulation

Stereoscopic HXR and EOVSA data constrain model showing consistent looptop and secondary sources linked to current sheet in X7.1 event

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We analyze the X7.1 flare on 2024 October 1 from NOAA AR 13842 using hard X-ray (HXR) imaging, microwave observations by the Expanded Owens Valley Solar Array (EOVSA), and a three-dimensional Magnetohydrodynamic (MHD) simulation. The flare was observed from two vantage points, with Solar Orbiter/Spectrometer Telescope for Imaging X-rays viewing the flare near the limb and Advanced Space-based Solar Observatory/Hard X-ray Imager and EOVSA observing it on the disk. We carried out a data-constrained MHD simulation using a nonlinear force-free field extrapolation as the initial condition and constrained the height of the non-thermal looptop source from stereoscopic HXR and microwave observations. The height is consistent between the stereoscopic analysis and the MHD simulation. A secondary non-thermal microwave source aligned with a southward plasma ejection corresponds to an elongated current sheet. Although the current sheet grows in multiple directions, the secondary microwave emission is observed only from the southern segment. This localization suggests reconnection in regions with different magnetic field strengths. Reconnection in strong-field regions produces flare arcades with dominant looptop emission, whereas reconnection in weaker southern regions gives rise to secondary microwave emission at higher altitudes. The height of the secondary source is consistent between the stereoscopic analysis and the MHD simulation. Microwave spectral fitting suggests a higher low-energy cutoff for non-thermal electrons in the secondary microwave source than in the main looptop source. This may reflect the transport of electrons pre-accelerated near the looptop source by the southward plasma ejection.

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astro-ph.SR 2026-06-30

Neural net extracts 3583 new BHB stars from LAMOST DR12

by Mingyuan Wang, Xiaoming Kong +3 more

MSFA-Net: An Advanced Deep Learning Model for Identifying Blue Horizontal-Branch Stars from LAMOST DR12

Two-stage model reaches 98 percent precision in binary refinement and delivers a larger homogeneous catalog of halo tracers.

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Blue horizontal-branch (BHB) stars are low-mass, core helium-burning objects with nearly constant luminosities, making them powerful tracers of old, metal-poor populations and valuable standard candles for mapping the Galactic halo. However, robustly identifying BHB stars from low-resolution spectra remains challenging. We present MSFA-Net, a two-stage framework developed for the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) DR12. By combining multi-scale convolutions with a soft frequency attention mechanism, MSFA-Net learns discriminative representations in both the wavelength domain and the Fourier-frequency domain. On the test set, the framework achieves a precision of 94.67% in the initial multiclass screening and 98.07% in the subsequent binary refinement. Applying the pipeline to LAMOST DR12, we retrieve 27,853 BHB candidate spectra. After spectral deduplication and removal of previously known objects, we identify 3583 new BHB stars, confirmed via Balmer-line profile fitting. We further estimate atmospheric parameters (Teff, log g, and [Fe/H]) using the machine-learning-based SLAM model and examine their distributions. A non-negligible subset shows unusually high log g and/or metallicities, which we interpret primarily as inference-related systematics rather than intrinsic properties. Photometric cross-matching with Gaia DR3 and color-magnitude diagrams provide an additional consistency check for the sample. The resulting catalog substantially enlarges the spectroscopically confirmed BHB sample from LAMOST and offers a homogeneous data set for studies of Galactic-halo structure and stellar populations.

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astro-ph.SR 2026-06-30

AD Leo superflare shows Balmer lines carry most chromospheric energy

by Younghun Oh, Seo-Won Chang +7 more

High Resolution Spectroscopic Analysis of Chromospheric Line Evolution during an Energetic Flare on AD Leo

High-resolution spectra find Ca II lines peak later than Hα, matching cumulative heating, with total energy comparable to largest solar flar

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Active M dwarfs exhibit frequent and energetic flares that provide a unique laboratory for studying chromospheric heating processes under extreme magnetic activity. To probe the flare process of M-dwarfs, we present a high-resolution ($R\sim30{,}000$) spectroscopic case study of a superflare on AD Leo, detected on 2023 March 14 using the Bohyunsan Optical Echelle Spectrograph (BOES). Such high-energy events are rarely captured with simultaneous multi-line spectroscopy, allowing us to trace the energy partition and temporal evolution of the chromospheric lines. Based on equivalent width variations, we found that the H$\alpha$ line radiated $8.8\times10^{30}$ erg, implying a total bolometric energy ($\sim10^{33}$ erg) comparable to the largest solar flares. The Balmer series dominated the energy budget; the individual Ca II H and K lines contributed 47.5% and 26.2% of the H$\alpha$ energy, respectively, while each Ca II infrared triplet line emitted $\sim$17-19%. We confirm that the delayed peak emission, previously reported for Ca II H&K, also occurs in the Ca II triplet and Na I lines. These delays are consistent with the Neupert effect, suggesting that cumulative heating governs the gradual phase emission. While this superflare resembles solar flares in general morphology, it also displayed systematic differences in chromospheric emission. It is likely that these differences reflect the distinct atmospheric structure and quiescent chromospheric conditions of M dwarfs, rather than fundamentally different flare physics.

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astro-ph.HE 2026-06-30

VLBI tracks magnetar kicks to test supernova dynamo origin

by Takuya Akahori, Sujin Eie +9 more

VLBI Astrometry of Magnetars

SKA-VLBI will expand the sample of measurable proper motions within radio outburst windows of months.

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The origin of the strongest magnetic fields in the Universe, i.e., the origin of magnetars, is a longstanding question. An enhanced dynamo effect in an irregular supernova explosion is a possible origin, which implies a stronger kick velocity and a higher proper motion of the magnetar compared to those of ordinary pulsars as well as an irregular morphology of the host supernova remnant (SNR). However, this hypothesis is not well studied yet, because there is a lack of precise measurement of the proper motion of magnetar and of identification of the host SNR. VLBI astrometry of magnetars is a unique tool to examine the hypothesis. In this chapter, we introduce the MONSTER (Monitoring Observations of the Neutron Stars That Evolve Rapidly) Project. SKA-VLBI's unprecedented sensitivity and the highest angular resolution will allow us to dramatically expand the survey volume in which we can measure the proper motion of magnetars within a radio outburst period of a few months.

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astro-ph.EP 2026-06-30

Brown dwarf transits evolved star every 4.8 days

by Akanksha Khandelwal, Shubhendra Nath Das +43 more

TOI-6884b: A low-mass brown dwarf transiting a slightly evolved star

Ground-based data fix TESS period alias and measure mass at 26 Jupiter masses for rare system

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We report the discovery of a low-mass transiting brown dwarf orbiting TOI-6884 (TIC~156514476, $T_{\rm mag}=11.4$) from NASA's \textit{Transiting Exoplanet Survey Satellite} (\textit{TESS}) mission. The \textit{TESS} light curves initially suggested an orbital period of $\sim$14.42~days; however, our high-precision ground-based radial velocity measurements and multi-epoch time-series photometry reveal this to be a harmonic alias. We determine the true orbital period to be $4.808264^{+0.000015}_{-0.000014}$~days and confirm the substellar nature of the companion. TOI-6884b has a mass of $26.32^{+0.98}_{-0.93}\,M_{\mathrm{J}}$, a radius of $0.927^{+0.51}_{-0.52}\,R_{\mathrm{J}}$, and resides on a nearly circular orbit ($e=0.067^{+0.010}_{-0.012}$). Its host star is a late F-type slightly evolved star with $M_\star = 1.410^{+0.075}_{-0.069}\,M_\odot$,\msun, $R_\star = 1.840^{+0.072}_{-0.073}\,R_\odot$, $\log{g} = 4.057^{+0.045}_{-0.039}$, $[{\rm Fe/H}] = 0.094^{+0.073}_{-0.068}$~dex, and $T_{\rm eff}=6330^{+180}_{-160}$,\mathrm{K}$. TOI-6884b is a key addition to the small population of well-characterized transiting brown dwarfs orbiting host stars that have evolved off the main sequence. The detection of such systems will contribute to our understanding of the dynamical histories and structural evolution of short-period substellar companions around evolved stars.

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astro-ph.SR 2026-06-29

Distorted radio waves map solar wind turbulence and fields

by K. Sasikumar Raja, Prasad Subramanian +4 more

Radio Wave Propagation as a Probe of the Solar Corona and Solar Wind

Broadening and scintillation measurements yield turbulence amplitude, heating rates, and magnetic topology; denser source sampling will trac

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Radio waves propagating through an inhomogeneous, turbulent medium such as the solar corona and solar wind become distorted, causing the initially plane wavefronts becomes corrugated and acquire an RMS phase deviation across the wavefront. This leads to observable effects such as angular broadening of radio sources or intensity scintillation. Such waves can be used to probe the solar wind through various techniques, including angular broadening and interplanetary scintillation observations. Such observations enable the study of several key properties, such as the phase structure function, amplitude of turbulence, density modulation index, solar wind heating rates, magnetic field topology, and dissipation scales. These phenomena provide critical insights into the physical processes governing the solar corona and solar wind and its interaction with radio waves, offering valuable constraints on both coronal and solar wind turbulence and coronal magnetic field configurations. Currently, the limited number of radio sources near the ecliptic restricts our observations. However, the SKA-Low and SKA-Mid are expected to detect a significantly larger number of radio sources, thereby providing deeper insights into the solar corona, solar wind, and heliosphere. Long-term observations will be crucial to understanding how the above-mentioned parameters vary with heliocentric distance and over the solar cycle.

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astro-ph.SR 2026-06-29

Delta Cephei curves align on shared phase

by Zuhoor Elahi, Wafa Gull

Semi-Empirical Pulsation Reconstruction of Delta Cephei with Photometry, Radial Velocities, and Temperature Constraints

Photometry, velocities and temperature data become consistent once radius scale is fixed, leaving that scale as the main uncertainty.

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We present a semi-empirical reconstruction of the pulsation behavior of the classical Cepheid delta Cephei using observed Johnson-V photometry, HARPS-N radial velocities, and published SPIPS pulsation-model curves. A cleaned AAVSO Johnson-V data set was phase folded with P = 5.366531 d, corrected for observer zero-point offsets, clipped for residual outliers, and fitted with a three-harmonic Fourier template. The resulting empirical template has Delta V about 0.833 mag, R21 about 0.382, R31 about 0.168, and a rise fraction about 0.287. After phase and vertical alignment, the published SPIPS V-band curve reproduces the empirical Johnson-V morphology with an RMS residual about 0.023 mag. A Fourier representation of the HARPS-N radial velocities gives a peak-to-peak velocity span about 40.82 km s^-1, corresponding to a preliminary radius-displacement amplitude about 4.81 solar radii for p = 1.317. Combining this radius curve with the SPIPS Teff(phi) curve yields a hybrid luminosity curve close to the published SPIPS luminosity curve. The adopted R0 = 43.7 solar radii scale gives a mean luminosity ratio L_hybrid/L_SPIPS about 1.04, while R0 = 44.9 solar radii gives about 1.10. A direct radius-scale comparison also favors the lower adopted radius scale, with an RMS offset of 0.864 solar radii relative to the SPIPS-implied radius, compared with 2.060 solar radii for the larger-radius case. These results show that the observed visual morphology, radial displacement, and temperature-driven luminosity variation are mutually consistent when placed on a common phase convention, while the absolute radius scale remains the dominant systematic.

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astro-ph.EP 2026-06-29

Algorithm selects 24 lines for 1.122 m/s RV precision

by Kanishk Pandey, Eric A. Ford +18 more

Improving the Precision of Line-by-Line Radial Velocities: A Data-Driven Iterative Algorithm for Spectral Line Selection

FLARES iteratively prunes lines on solar spectra to beat full lists and benchmarks while using far fewer measurements.

abstract click to expand

Independent analysis of individual spectral lines, or line-by-line (LBL) analyses, can improve upon standard cross-correlation function (CCF) methods for measuring radial velocities (RVs) because they preserve critical information about individual line shape changes that can be caused by stellar activity. In this work, we measure LBL RVs of 3,830 spectral lines across 383 days of NEID solar observations. Our LBL approach achieves an RV RMS of $2.012~\mathrm{m\,s^{-1}}$, which is slightly lower than the $2.129~\mathrm{m\,s^{-1}}$ achieved by a CCF approach using a shared line list. Then, we describe and benchmark several methods for selecting line lists based on line properties such as depth and intrinsic RV scatter. We find that these subsets have a lower RV RMS compared to either the full line list or random subsets of equal size. Motivated by these results, we present FLARES (Filtering Lines for Accurate Radial-velocity Exoplanet Search), an iterative line-selection algorithm. FLARES selects candidate spectral lines with extreme values of multiple line metrics and properties such as depth, signal-to-noise ratio, and detector position, and preferentially rejects lines whose removal produces the largest decrease in the weighted RV scatter. FLARES achieves an RV RMS of $1.122~\mathrm{m\,s^{-1}}$ using just 24 lines and performs better than the benchmark methods. We perform Monte Carlo simulations and show FLARES is robust and reproducible. Comparisons to alternative line lists chosen to have properties similar to the best FLARES-selected lines demonstrate that FLARES is successfully identifying line properties that lead to effective line lists for future extreme-precision RV measurements.

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astro-ph.SR 2026-06-29

Third-order Fourier fit sets Delta Cephei Johnson-V template

by Zuhoor Elahi, Wafa Gull

A Reproducible AAVSO Johnson-V Fourier Template for the Prototype Cepheid Delta Cephei

N=3 model from 242 AAVSO points gives 0.8544 mag amplitude and 0.2885 rise fraction as benchmark.

abstract click to expand

We present an empirical Fourier reconstruction of the observed Johnson-V light curve of the prototype Classical Cepheid Delta Cephei. The goal is not to infer a full physical stellar model but to establish a reproducible observed-light-curve benchmark for later comparison with nonlinear pulsation, synthetic photometry, Baade-Wesselink/SPIPS, GYRE-supported, and independent hydrodynamic calculations. Using an adopted period of Pobs = 5.366531 d, 244 AAVSO Johnson-V measurements were filtered to a cleaned sample of 242 points after rejecting two extreme outliers. The cleaned data span 355.09259 d and were phase folded using an empirical bright-maximum epoch of JD = 2460851.395800. We fit a low-order Fourier model to the phased light curve and adopt a third-order template as the preferred empirical morphology representation. The adopted N = 3 fit gives A0 = 3.9031, A1 = 0.3434 mag, A2 = 0.1428 mag, and A3 = 0.0531 mag, corresponding to R21 = 0.4159 and R31 = 0.1547. The template has a full Johnson-V amplitude of Delta V = 0.8544 mag, a rise fraction of frise = 0.2885, and an asymmetry index of Aasym = 0.4230. Bootstrap uncertainties are reported in the manuscript. Fourier orders N = 4-6 reduce the RMS residual by only about 0.0012 mag relative to the N = 3 model, so the third-order representation is retained as the simplest adequate empirical template. Observer-level residual diagnostics show that the remaining scatter is not purely random. This paper provides an observational morphology target rather than a physical explanation of the pulsation.

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astro-ph.HE 2026-06-29

Choked jet model matches GRB 170817A delay and luminosity

by Matteo Pais, Riccardo Ciolfi +1 more

Modelling the delayed shock-breakout emission following jet-launching binary neutron star mergers via relativistic MHD simulations

MHD simulations show the gravitational-wave to electromagnetic delay and peak signal favor a substantially choked jet over early breakout ca

abstract click to expand

In binary neutron star (BNS) mergers launching a relativistic jet, an electromagnetic (EM) signal is produced when the jet-driven shock breaks out of the merger ejecta. The observed time delay of this shock-breakout (SBO) emission with respect to the gravitational-wave (GW) signal from the merger provides a powerful probe of the physical conditions governing jet launching and early-time jet propagation. Considering different models of jet propagation in realistic post-merger environments, we investigate the SBO emission and corresponding GW-EM delay that would be observed depending on the viewing angle and the assumed ejecta opacity. We perform relativistic MHD simulations of jets propagating through a post-merger environment directly imported from the outcome of a previous BNS merger simulation. We also introduce a specific procedure to faithfully reconstruct the early dynamical ejecta up to their natural front. The evolution is followed in 3D up to 0.6 s and then continued imposing axisymmetry and higher resolution. Varying jet launching time and luminosity, we identify three representative models spanning regimes from early breakout to extended jet choking. For each case, we track the jet-driven forward shock up to the photosphere and compute the angle-dependent bolometric SBO luminosity, assuming full conversion of the thermal energy within the shocked material into radiation, and taking into account non-radial photon propagation, relativistic Doppler shifts, and light-travel-time effects. We consider two opacity values spanning a factor of 10. We find that the GW-EM delay depends weakly on both viewing angle and ejecta opacity, making it a robust diagnostic for constraining models. Comparing with GRB 170817A, the model resulting in a substantially choked jet provides the most plausible peak bolometric luminosity and the closest match to the observed GW-EM delay and signal duration.

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gr-qc 2026-06-29

Quark star models fit all current mass and radius data with 4-7 kHz modes

by G. Panotopoulos, A. Rincon +1 more

Radial oscillations of quark stars in light of current astrophysical constraints: A comparative study

Frequencies lie in the gravitational-wave detection band and accommodate the low-mass object in HESS J1731-347.

abstract click to expand

We investigate the structural and oscillatory properties of isotropic strange quark stars within General Relativity, focusing on three physically motivated equations of state: the color flavor locked (CFL) phase, an interacting quark matter model, and a linear (causal) equation of state. By numerically solving the Tolman Oppenheimer Volkoff and radial perturbation equations, we construct equilibrium stellar sequences and compute oscillation spectra across three representative masses (0.77, 1.40, and 2.00 solar masses). Our analysis is focused on two diagnostics: (i) mass to radius profiles and (ii) radial mode eigenfrequencies with large frequency separations. We compare theoretical predictions against multimessenger constraints from NICER X ray timing of key pulsars, the massive pulsars at two solar masses, and the low mass compact object in HESS J1731--347. All three equations of state yield maximum masses exceeding 2 solar masses with canonical mass radii of (10--12) km, satisfying current observational bounds. Fundamental mode frequencies span (4--7) kHz, with asymptotic large separations differing among the models. These elevated frequencies lie within the detection band of current and next generation gravitational-wave observatories, offering potential asteroseismic signatures for distinguishing strange quark stars from hadronic neutron stars in post merger emission. Our results demonstrate that self bound quark matter naturally accommodates the sub solar mass configuration of HESS J1731--347, reinforcing the viability of strange quark star interpretations.

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