The Astrophysical Journal - latest papers

Modeling YSO Jets in 3D. III. Dependence of Accretion and Jet Properties on Stellar Magnetospheric Field Strength and Rotation

Yisheng Tu, 以晟涂, Zhi-Yun Li, Zhaohuan Zhu, 照寰朱 and Kass Bell — 2026-08-23T23:00:00Z

Observations of young stellar object systems reveal a wide diversity of jet properties, from well-collimated bipolar jets to unipolar jets and systems with no detectable jet. Both prograde and counter-rotating jets are reported, raising questions about how jets are launched and how their properties relate to the underlying star-disk system. Using 3D nonideal MHD simulations, we present a suite of models in which jet properties depend sensitively on stellar rotation and magnetic field strength. In all models, jets are launched from “two-legged” magnetic field lines anchored to both the star and the turbulent, magnetically elevated disk surface, with interactions at the disk surface crucial for mediating the magnetosphere–disk coupling. The axial jet and its surrounding disk wind form a characteristic “spine-tower” structure: the spine is the kinematically dominated jet along open field lines threading the star, and the tower is the surrounding toroidal-field-dominated disk wind. The stability of this structure depends on the balance between the spine’s stabilizing power and the tower’s destabilizing power; if the tower dominates, the disk wind can choke the jet, producing asymmetric or no jets. This relationship allows an upper limit estimate on the toroidal magnetic field strength in the disk wind-launching region using observed outflow properties. Counter-rotating jets naturally appear in models, particularly with nonrotating stars, showing that the classical rotation–poloidal velocity relation does not reliably indicate the jet-launching radius. Instead, it could be used to trace the stellar rotation rate, offering a potential observational diagnostic of stellar spin.

CHANG-ES XL: Magnetic Field Structures in the Disk and Halo of NGC 891

2026-08-23T23:00:00Z

We present new Karl G. Jansky Very Large Array S-band (2–4 GHz) observations of the edge-on spiral galaxy NGC 891, complemented by C-band data, to investigate the structure of its radio continuum halo. Using rotation measure synthesis we detected an extended polarized halo, with most spatially extended polarized emission confined to Faraday depths within ±150 rad m−2. We identified a localized region in the northeast side of the galaxy that shows an enhancement in polarized intensity (not in percentage polarization). By combining the radio data with Hα and diffuse X-ray maps, we discuss a possible origin for this structure: a superbubble powered by clustered supernovae. Across the disk and halo, the percentage polarization decreases toward the midplane but shows a mild wavelength dependence, despite the edge-on orientation of NGC 891. This behavior implies that the depolarization cannot be dominated by small-scale Faraday rotation within the disk. Instead, it is possible that most of the observed polarized emission arises on the Earth-facing side of the galaxy. Our peak rotation measure map shows a smooth transition along the major axis, consistent with a large-scale axisymmetric magnetic field. Using Hα and UV data, we analyzed the distribution of H ii regions and found that they are parts of different spiral arms. We also identified a faint, isolated H ii region at a galactocentric radius of 16.9 kpc, with both Hα and far-UV counterparts, indicating star formation outside the thin disk.

Simulation to a Newborn Supernova Remnant from a Low-mass Iron Core Star

2026-08-23T23:00:00Z

Supernova remnant observations show a high degree of asymmetry, mixing, and inhomogeneity. These asymmetries are seeded during the early seconds of the explosion and are further enhanced and modified as the shock and ejecta move through the stellar progenitor and into the circumstellar medium. We present simulations of a 9.6 M⊙ zero-metallicity progenitor initialized after shock revival and evolved for several years when the ejecta is in the circumstellar medium. A suite of 1D and 2D simulations examines the effects of neutron-star wind and radioactive decay heating. In 1D, decay heating forms a low-density bubble that suppresses the reverse shock. While in 2D, the heating is localized to metal-rich pockets, inflating them and compressing the surrounding material into dense shells. In 3D, the neutron-star wind and decay heating modify the plume morphology, producing more large-scale structures. The extended plume morphology leads to an asymmetrical shock breakout. After breakout, the leading plumes cannot keep up with the shock front, resulting in deceleration and fragmentation by the reverse shock while retaining the large-scale asymmetry. The projected ejecta morphology and velocities are strongly viewing angle dependent. The relatively uniform metal-rich distribution does not resemble the strongly inhomogeneous ejecta structure of Cas A. The 160-isotope decay network shows that 24.4% of the radioactive heating comes from decay chains other than the canonical 56Ni chain. The low explosion energy, low 56Ni yield, and Ni/Fe ratio greater than unity suggest an observational signature similar to an electron capture supernova.

Inferring 3D Coronal Magnetic Fields through Seismology-assisted Inversions of IQU-only Spectropolarimetric Observations

Alin Răzvan Paraschiv — 2026-08-23T23:00:00Z

The routine measurement of the Stokes IQUV signals of emission lines in the solar corona is still a challenging endeavor, particularly for observations using small-aperture instruments. Therefore, recent studies have explored the use of coronal seismology and propagating Alfvénic waves as alternative diagnostics of the coronal magnetic field. In particular, Z. Yang et al. showed that plane-of-sky (POS) phase-speed measurements provide a direct and consistent diagnostic of the POS magnetic-field component (BPOS). Building on recent theoretical advances in solar coronal polarization, we devise a novel inversion scheme and extended the CLEDB software package to exploit Stokes IQU observations of two coronal emission lines combined with coronal seismology-derived BPOS estimations. Using this framework, we perform a comprehensive statistical analysis demonstrating that this combination of diagnostics allows us to infer both magnetic-field orientation and strength with an accuracy comparable to that of Stokes IQUV spectropolarimetry. This type of diagnostics is particularly suited for the Fe xiii 1074.7 and 1079.8 nm line pair routinely observed by new-generation instruments such as DKIST Cryo-NIRSP, DL-NIRSP, MLSO CoMP/UCoMP, and targeted by the future COSMO and CORSAIR efforts.

Mid-infrared Colors Vary with Galactic Environment: Contrasting Star-forming Disks, Young Centers, and Quiescent Star-formation Deserts

2026-08-23T23:00:00Z

We present 50–100 pc-resolution JWST/MIRI and NIRCam measurements of mid-infrared (mid-IR) color variations in the diffuse interstellar medium (ISM) of 71 nearby star-forming galaxies from the PHANGS-JWST survey. Mid-IR emission traces the dust column density, intensity (U) and hardness of the interstellar radiation field, and the physical state (charge, size) and abundance of polycyclic aromatic hydrocarbons (PAHs). Mid-IR colors that trace PAH band ratios remain fairly constant in the diffuse ISM of star-forming disks. However, they show stark variations in extreme environments: highly star-forming central molecular zones (CMZs) and star formation deserts/quiescent bulges. In CMZs, PAH-to-continuum (3.3/21, 7.7/21, and 11.3/21 μm) and the 10/21 μm continuum colors are 0.2–0.4 dex lower than in normal disks. We attribute this to higher U based on the far-infrared dust colors and the high 21 μm/ΣMol, which we suggest to be a good tracer of U outside star-forming regions. Meanwhile, star formation deserts show low 7.7 μm PAH emission, resulting in low 7.7/21 μm and 7.7/11.3 μm, while all other mid-IR colors remain typical. This suggests the presence of more neutral PAHs in star formation deserts, where low 7.7 μm likely reflects ISM conditions similar to early-type and elliptical galaxies. All environments form part of a continuous trend in 7.7/11.3 μm versus specific star formation rate.

The Age–Thickness Relation as a Tracer of the Merger History of Disk Galaxies

2026-08-23T23:00:00Z

In the hierarchical framework of galaxy formation, disk galaxies are shaped by a sequence of mergers and interactions, yet reconstructing this history from observations remains challenging. We show that the merger history of a galaxy leaves measurable imprints in the vertical structure of its stellar disk. Using Milky Way analogs from the TNG50 simulations, we demonstrate that the age–thickness relation, quantified by the dispersion of vertical stellar positions (Δz), encodes both the dynamical heating of preexisting stars and the birth conditions of stars formed during perturbed phases. Major mergers produce pronounced, step-like features in the Age–Δz relation, reflecting strong disk heating and subsequent re-formation of a thin disk, while flyby interactions generate weaker, localized enhancements associated primarily with disturbed star formation. We show that this diagnostic is robust across different locations within the disk and largely insensitive to fractional distance uncertainties lower than 20%; though, its temporal resolution is limited by uncertainties in stellar ages. Because the Age–Δz relation relies only on stellar positions and ages, it provides an observationally accessible alternative to traditional kinematic diagnostics. With current and upcoming surveys mapping the Milky Way with unprecedented precision, this framework offers a new avenue for reconstructing the merger history of our Galaxy and probing the dynamical evolution of disk galaxies across cosmic time.

Variability of the X-Ray-obscuring Wind in Mrk 335 with the XMM-Newton Reflection Grating Spectrometer

2026-08-23T23:00:00Z

Transient X-ray obscuration in Seyfert 1 galaxies likely arises from clumpy accretion-disk winds near the broad-line region (BLR), but the wind structure and short-timescale variability are difficult to measure because high-resolution spectra are often suppressed during deep low states. We analyse a coordinated XMM-Newton + NuSTAR campaign on Mrk 335 in 2021 June, with long-term Neil Gehrels Swift Observatory monitoring, capturing the source in an intermediate-flux state with strong Reflection Grating Spectrometer (RGS) absorption features. We model the broadband spectral energy distribution to determine the ionizing continuum for self-consistent photoionization modelling of the RGS spectra. The stacked RGS spectrum requires three photoionized absorbers with , 2.97, and 1.91, outflowing at ∣vout∣ ≃ 5800, 3200, and 2100 km s−1, respectively. Their properties are consistent with the three-phase obscurer reported in 2009, indicating that a similar multiphase obscuring wind can persist over decade timescales. Using five consecutive RGS observations, we track the wind evolution on day timescales and find strong variability in column density and ionization in all phases, together with smaller but coherent velocity changes. During a flare, the low-ionization phase shows a significant drop in opacity, while in the subsequent epoch all phases show increased outflow velocities, suggesting a possible connection between continuum variability and changes in the line-of-sight absorber. The high-ionization phase responds most directly to changes in ionizing luminosity, while the lowest-ionization phase shows at most a delayed response. Order-of-magnitude constraints place the obscurer at BLR scales ∼ 103–105Rg, with kinetic power potentially reaching the percent level of Lbol for plausible assumptions on geometry and clumpiness.

In Situ and Near-Sun Properties of Coronal Mass Ejections for Two Different Types of Events: From Active Regions versus from Quiescent Regions

Jie Zhang, Lan K. Jian, Suman K. Dhakal and Sachiko Akiyama — 2026-08-23T23:00:00Z

Severe space weather is caused by coronal mass ejections (CMEs). While the chain of CME activities from the Sun to Earth has been well tracked for some individual events, the statistical relations between the physical properties of CMEs near the Sun and those of their counterpart interplanetary CMEs (ICMEs) have not been well investigated. In this article, we provide a comprehensive study of a large set of properties for all 66 Earth-affecting CMEs during 2011–2013. Among them, 32 (48%) CMEs originated from compact and stronger magnetic field regions, i.e., active regions (ARs), while 34 (52%) CMEs originated from larger but weaker-field quiescent regions (QRs). The AR-CMEs are much faster than QR-CMEs near the Sun, with average true speeds of 1086 and 711 km s−1, respectively. We find that, at 1 au or near Earth, the differences between the two contrasting types are no longer prominent, but not fully diminished. While the charge states and velocities remain statistically different, other ICME properties, including magnetic field strength, plasma β, proton temperature, helium abundance, and others, do not differ with statistical significance. Interestingly, QR-CMEs and AR-CMEs have nearly equal chances of driving a forward shock at 1 au (68% versus 69%). These results indicate that the evolution of CMEs during their propagation from the Sun to Earth has significantly reduced many differences in properties near the Sun between the two types of events.

Determination of Absolute Parameters and Investigation of Period Changes for the Double-lined Algol-type Binary UW Boo

Hui-Ting Zhang, Sheng-Bang Qian, Wen-Ping Liao, Lin-Jia Li and Li-Ying Zhu — 2026-08-23T23:00:00Z

UW Boo is an Algol-type eclipsing binary with a period of 1.0047 days. We report the first detection of the double-lined spectroscopic nature of UW Boo through a joint analysis of a multisource spectroscopic dataset. This allows the derivation of precise radial velocities for both components, yielding a mass ratio of qsp = 0.318 ± 0.006. Combined analysis of the high-precision TESS light curve and radial velocity curves using the Wilson–Devinney code provides a complete set of binary solutions. The masses of the two components are determined to be M1 = 1.35 ± 0.02 M⊙ and M2 = 0.43 ± 0.01 M⊙. The investigation of orbital period changes is extended to a century-long baseline by incorporating historical eclipse timings from the digitized Harvard plates (DASCH project) with TESS observations. It is discovered that two cyclic modulations are superimposed on a long-term period decrease with a rate of dP/dt ≈ −3.16 × 10−8 day yr−1. The observed secular decrease can be interpreted as a result of nonconservative mass transfer dominated by the magnetic stellar wind. The possible origins of the cyclic modulations are investigated, which may be attributed to the light-travel-time effects caused by the presence of low-mass companions. This multitechnique investigation positions UW Boo as a benchmark system for probing mass transfer and loss, magnetic activity, and the presence of additional components in Algol-type systems.

ICM-SHOX. III. The Case of MACS J0018.5+1626, a Radio Relic That Looks Like a Radio Halo?

2026-08-23T23:00:00Z

We present the first detailed numerical modeling of the radio emission from MACS J0018.5+1626 as part of the Improved Constraints on Mergers with Sunyaev–Zel’dovich (SZ), Hydrodynamical Simulations, Optical, and X-ray (ICM-SHOX) project. By matching X-ray, thermal and kinetic SZ, optical, and lensing observables to simulations, the ICM-SHOX pipeline indicates that MACS J0018.5+1626 is undergoing a binary merger close to pericenter passage and is observed along a line of sight nearly aligned with the merger axis. We perform 3D magnetohydrodynamics simulations of binary cluster mergers coupled to tracer particles and a Fokker–Planck solver to model the radio emission. Exploring variations in the most likely initial conditions within the ICM-SHOX parameter space, such as the relative cluster velocity and impact parameter, we find that the resulting merger configuration consistently produces two merger-driven shocks with typical average Mach numbers –3 with corresponding standard deviations of –1.5. Within this framework, we examine the cluster conditions under which standard diffusive shock acceleration can reproduce LOFAR observations. In particular, we discuss the possibility that the apparent radio halo seen by LOFAR arises from the superposition of two radio relics viewed nearly face on.

What Do Gravitational-wave Observations Tell Us About Luminous Red Novae?

2026-08-23T23:00:00Z

Luminous red novae (LRNe) have been argued to be related to the ejection of common envelopes (CEs) in binary star systems. Ejection of CEs leads to tightened stellar orbits capable of forming CBs that merge in Hubble time. As these mergers are seen by gravitational-wave (GW) detectors such as LIGO, Virgo, and KAGRA (LVK), we ask what the merger rates of CBs in LVK tell us about the fraction of LRNe that lead to the formation of CBs that merge in Hubble time. Using the observed volumetric rates of LRNe from the Zwicky Transient Facility and of compact binary mergers from LVK observations, we derive limits on the fraction of LRNe that produce CBs that merge in Hubble time. Assuming the LRNe rate closely follows the star formation rate at any redshift, we use the delay time distribution models for CBs to compute the compact binary merger rate. A comparison of this merger rate with the latest volumetric rates of compact binary mergers from the fourth GW Transient Catalog (GWTC-4) at the present epoch of LVK allows us to constrain the above fraction. We find that only a fraction as small as ∼10−3 (median) of the LRNe correspond to the GW-observed binary neutron star and neutron star–black hole mergers. This potentially implies that the majority of the LRNe population will not lead to mergers of compact objects, but other end products, such as stellar mergers.

Infrared Line Diagnostics Fail to Constrain Sgr A*’s UV Output

2026-08-23T23:00:00Z

Sgr A⋆, the 4 × 106M⊙ supermassive black hole at the Galactic center, exhibits frequent flaring with X-ray luminosities of LX ∼ 1035–1036 erg s−1, while its ultraviolet (UV) emission remains unconstrained due to extreme extinction (AV ∼ 30 mag). We use JWST/MIRI time-resolved spectroscopy of the central region to search for mid-infrared emission line variability driven by Sgr A⋆ flares, comparing the results to CLOUDY photoionization models spanning flare luminosities of LUV = 1032–1039 erg s−1. We detect no continuum-correlated variability in any mid-infrared line, including [Fe ii] (5.34 μm), [Ne ii] (12.813 μm), [Fe ii] (17.936 μm), and [S iii] (18.713 μm) over lags of ∼1–8 hr. Despite expectations of a flare-driven response, we show that the lack of variability is consistent with the physical conditions in the spatially extended line-emitting gas, where light-crossing timescales of ∼0.1–10 days and recombination and cooling timescales much longer than the variability timescales suppress any observable response to individual flares. We further find that the modeled infrared spectra are dominated by continuum emission rather than isolated line emission. The brightest predicted lines are intrinsically weak (lower than 10−5 mJy), and their detectability is further reduced by the large kinematic broadening expected at the CLOUDY-predicted emitting radii, reducing their contrast against the continuum. Extending the analysis to higher-ionization mid-infrared and near-infrared lines does not improve sensitivity. These results demonstrate that infrared emission lines trace a steady-state radiation field rather than individual flaring events, and therefore infrared line diagnostics cannot be used to constrain the instantaneous UV flux of Sgr A*.

MHD Modeling of Magnetic Flux Evolution Around Solar Maximum by the Coronal Model COCONUT

2026-08-23T23:00:00Z

In this paper, we simulate the magnetic flux evolution at different heliocentric distances during two solar-maximum Carrington rotations (CRs) using the time-evolving coronal magnetohydrodynamic (MHD) model COCONUT to investigate the “open flux problem.” The simulated open magnetic flux (OMF) near the solar surface is comparable to that derived from in situ observations by PSP and WIND satellites and is about 5 times larger than that derived from SDO coronal hole (CH) observations, and the variation in the simulated radial solar wind speed is consistent with the evolution of the OMF evaluated around the corresponding solar disk center. We find that the OMF is reduced by up to 45% from 1.01 Rs to 0.1 au and increases with a higher-resolution mesh. The OMF decreases mainly within 3 Rs, where the closed magnetic flux drops more rapidly, from about 60% of the total magnetic flux at 1.01 Rs to about 4% at 3 Rs. A moderate adjustment to the heating source term can effectively regulate the simulated OMF. Preprocessing the photospheric magnetograms with a potential-field solver that removes many high-order spherical-harmonic components reduces the OMF in the low corona while having little impact beyond 3 Rs. Additionally, the ratio of the maximum to the minimum OMF can reach 1.4 during a single solar maximum CR. These findings highlight the necessity of considering higher grid resolution, more realistic heating mechanisms, and the time-evolving regime of coronal MHD modeling when further addressing the open flux problem.

Magnetohydrodynamical Opening of Dust Traps in Protoplanetary Disks

Sergey Khaibrakhmanov and Vitaly Akimkin — 2026-08-23T23:00:00Z

Observed ring-like structures in protoplanetary disks are often interpreted as local pressure maxima, which induce efficient dust concentration. We revisit this paradigm considering the effect of the large-scale magnetic field stresses on the gas rotation speed. Our simulations show that the magnetic field can be dynamically strong and cause 1%–2% deviation from the Keplerian rotation at the periphery of a typical turbulent disk with dust grains of size >1 μm. This effect increases the inward drift speed of large grains characterized by a Stokes number of 0.01–0.1 by up to two times in our simulations. Importantly, such MHD deviation from the Keplerian rotation does not depend on the local gas pressure gradient and leads to drift toward the star only. The fast drift induced by this effect can cancel out the outward drift caused by the positive pressure gradient at the inner edge of a ring and open up the dust trap. For the disks with turbulence parameter α = 10-3, this effect appears in the rings with a half width of 10 au and a density contrast up to 60% (200% for α = 10-2). Thus, the presence of a large-scale magnetic field in protoplanetary disks either completely prevents or imposes stricter conditions for dust accumulation and the onset of the streaming instability in the density rings in protoplanetary disks.

Supermassive Black Hole Assembly from Heavy Seeds with Dynamical Friction in the BRAHMA Simulations: Implications for JWST, LISA, and the Local Universe

2026-08-23T23:00:00Z

The James Webb Space Telescope (JWST) discoveries of supermassive black holes (BHs) at z ≳ 5 may provide key insights into their seeding origins. Using new [18–72 Mpc]3BRAHMA cosmological simulations, we investigate how variations in heavy-seed prescriptions, coupled with a subgrid dynamical friction model, shape BH populations at z ∼ 5 and ∼ 0. We consider two “lenient” seed models, in which all halos containing sufficiently dense and metal-poor gas form ∼104 and ∼105M⊙ seeds, and a “strict” seed model, in which ∼105M⊙ seeds form only under additional constraints motivated by direct collapse BH formation. By z ∼ 5, all models produce M*–MBH relations broadly consistent with the observed local Universe for M* ≳ 109M⊙ galaxies, but only the lenient scenarios generate systems near the upper envelope of the observed local scatter. In galaxies hosting MBH ∼ 108–109M⊙ BHs, lenient production of ∼105M⊙ seeds also produces multiple overmassive systems with MBH/M* ≳ 0.01. Although their growth is dominated by seeding and mergers, these systems reach luminosities of ∼1043–1045 erg s−1, comparable to those inferred for JWST-detected BHs. As a key observational signature, the lenient seed models yield merger rates of ≳100 yr−1 and near-unity local BH occupation fractions even in galaxies with M* ≲ 107M⊙. In contrast, the strict seed model produces merger rates of only ∼1 yr−1 and local occupation fractions of ≲10% for galaxies with M* ≲ 108M⊙. Future gravitational-wave event rates and measurements of local BH occupation fractions will therefore provide strong constraints on the dominant pathways responsible for high-redshift BH assembly.

Understanding the Travel-time Asymmetry of Acoustic Waves in Sunspots with Time–Distance Helioseismology

2026-08-23T23:00:00Z

Mapping the subsurface structure and flow field of sunspots has been a challenging task for helioseismology. In this work, we investigate the propagation of acoustic waves in a sunspot in NOAA active region 11312 using time–distance helioseismology. Travel-times of waves traveling into and out of the sunspot are measured as functions of travel distance and azimuthal angle relative to the local radial direction. The same time–distance analysis is also applied to simulated data based on a magnetohydrostatic (MHS) model of the sunspot, and forward modeling of travel-times is performed using ray tracing based on both the MHS sunspot model and a magnetohydrodynamic (MHD) simulation. We find that both ingoing (traveling from the quiet area into the sunspot) and outgoing waves (traveling from the sunspot into the quiet area) have shorter travel-times than in the quiet Sun, with travel-time reductions of up to ∼40 s. The magnitude of the mean time shift is largest for waves traveling along the radial direction at small travel distances. A clear asymmetry is detected between ingoing and outgoing waves: outgoing waves generally exhibit shorter travel-times. This asymmetry is strongest for the radial direction and small travel distances, with differences exceeding 1 minute for 3.5 and 4.5 mHz waves. From the results of both observations and models, our analysis indicates that the overall reduction in travel-time could be primarily caused by the combined effects of Wilson depression, magnetic field, and wave-speed perturbations, while the ingoing–outgoing asymmetry could be partly attributable to subsurface flows. Although the forward-modeling results reproduce several qualitative features of the observations, quantitative discrepancies remain, highlighting limitations of current sunspot models and ray-theoretical approximations.

Dynamics and Detectability of Long-lived Nonaccretion Phases for Massive Black Hole Binaries in Cold Thermally Regulating Disks

Christopher Tiede, David O’Neill and Daniel J. D’Orazio — 2026-08-23T23:00:00Z

We investigate whether the nonaccreting phases found in thin, locally isothermal circumbinary disks survive when the disk thermodynamics are evolved self-consistently. We present grid-based hydrodynamics simulations of circumbinary accretion with an energy equation that includes viscous and hydrodynamic heating coupled to radiative blackbody cooling in the high-Mach number regime. We find that, although gas accumulates and heats at the far edge of the circumbinary cavity, the regions that launch accretion streams remain comparatively cold, leading to potentially long-lived suppression of the binary accretion rate as the large-scale feeding rate is reduced towards the Eddington limit. This runaway nonaccretion problem, however, is weakened relative to locally isothermal solutions. Despite their low accretion rates, binaries interacting with disks in a nonaccreting phase can remain sufficiently luminous and variable at optical and near-infrared frequencies to be detectable in upcoming wide-field surveys such as LSST and the Roman Space Telescope. Because of the effective truncation of the surrounding disk, though, such systems are comparatively faint in high energy, photoionizing emission, and may therefore appear as intrinsically X-ray–weak active galactic nuclei with weak or absent emission line features. We additionally suggest an update to grid-based sink prescriptions for approximating mass loss across an unresolved horizon when including an energy conservation equation.

Probing the Mass-loss Histories of Type IIn and Type II-L Supernovae with Late-time Radio Observations

2026-08-23T23:00:00Z

We present Very Large Array observations of 16 Type IIn and Type II-L supernovae (SNe IIn and SNe II-L) at ≈1000–7000 days after explosion, probing circumstellar matter (CSM) at distances >1016 cm from the progenitor. At these radii, the data directly constrain the density structure encountered by the shock. We detect radio emission from four SNe (1998S, 2005ip, 2008fq, and PTF11iqb) with the remaining 12 yielding upper limits of νLν < 1035–1036 erg s−1 at 3–11 GHz. The detected sources span approximately two orders of magnitude in radio luminosity, consistent with a broad distribution of CSM densities. All detected sources exhibit steep spectral indices (α ≲ −0.4) consistent with optically thin synchrotron emission; their two-frequency spectral evolution is also consistent with, but does not uniquely require, models in which internal free–free absorption contributes at earlier epochs. Under simplified shock–CSM models, we obtain order-of-magnitude limits on of ≲10−6–10−3M⊙ yr−1/(100 km s−1), subject to substantial systematic uncertainties in microphysical parameters and absorption prescriptions. The detection of the intermediate SN IIn/SN II-L object PTF11iqb at luminosities between classical SNe IIn and SNe II-L is consistent with a continuum between these subtypes in CSM interaction strength. Our limits further suggest that SNe IIn and SNe II-L are not separated by long-term mass-loss rate at the radii probed here, but chiefly by the presence and strength of dense circumstellar material immediately before explosion.

Mineralogical Characteristics of the Lorentz and Coulomb-Sarton Basins Reveal Early Magmatic Activity on the Lunar Farside

Jiaqi Kong, Haijun Cao, Xuejin Lu, Jian Chen, Ziyi Jia and Zongcheng Ling — 2026-08-23T23:00:00Z

Mg# (molar Mg/(Mg+Fe)) is a critical geochemical indicator for quantifying the evolution of the lunar crust, providing essential insights into regional compositional variability, crustal differentiation processes, and the crystallization history of the early lunar magma ocean (LMO). The Lorentz and Coulomb-Sarton (LCS) basins on the lunar farside exhibit significant magnesium anomalies in global surface chemistry maps that challenge traditional models of lunar crustal development. By integrating multisource lunar remote sensing data, we applied spectral parameter techniques and the Hapke radiative transfer model to assess the mineralogical characteristics of the LCS region and produce an updated geological map. The results reveal that the LCS region is predominantly dominated by plagioclase (>72.1 wt%), primarily in the form of ferroan anorthosites (FANs) with low-Mg# (<70) lithologies. Regions of elevated Mg# (>70) are concentrated in the western and northern portions of the Coulomb-Sarton basin and the central ring of the Lorentz basin. These localized anomalies correspond to Mg-rich lithologies that are interpreted as magnesian anorthosites derived from deeper crustal levels and subsequently exposed by impact excavation. This spatial pattern is consistent with a vertically stratified crustal structure, in which the upper crust consists predominantly of primordial FANs formed during the early LMO solidification. While deeper crustal materials may be related to magmatic intrusion from mantle-derived melts, they are intermittently exposed by large impact events and basin-scale modification processes. These findings provide new insights into the mineralogy and composition of the lunar farside highlands and constraints on the complex crustal evolution of the LCS region.

Bayesian Geometrical Modeling of IXPE Polarization Angle Curves of the Magnetars 1E 2259+586 and 1E 1547.0−5408

2026-08-23T23:00:00Z

X-ray polarimetry directly probes the radiation geometry and large-scale magnetic configuration of magnetars. We present a uniform Bayesian comparison between a dipole-dominated classical rotating vector model and a modified rotating vector model (MRVM) including a first-order magnetospheric twist correction. The models are applied to the phase-resolved Imaging X-ray Polarimetry Explorer (IXPE) polarization position angle (PA) curves of 1E 2259+586 and 1E 1547.0−5408. Parameters are inferred with a PA-level likelihood, and the models are compared using χ2, the Akaike information criterion, Bayesian information criterion, and Bayesian evidence. For 1E 1547.0−5408, we also test radio-derived geometrical constraints using radio-informed priors and radio-fixed fits. The current IXPE PA data for both sources are consistent with a dipole-dominated geometry and do not require a significant global twist. The MRVM gives only a marginal improvement for 1E 2259+586, with a Bayes factor of ≃3.3, and no meaningful improvement for 1E 1547.0−5408, with a Bayes factor of ≃1.29. We confirm that, for 1E 1547, the nearly aligned radio geometry is not ruled out, but the radio rotating vector model central geometry is not preferred by the X-ray PA data alone. The two sources show different impact angles, suggesting that magnetar X-ray polarization diversity reflects both viewing geometry and source-dependent emission physics. This work provides a framework for future Stokes-level and multiepoch polarimetric studies with missions such as eXTP.

Substellar Strange Quark Matter Objects: Predicting a New Class of Highly Compact Candidates

Jonathan Joás Zapata Campos and Rodrigo Negreiros — 2026-08-23T23:00:00Z

We investigate the existence of highly compact substellar objects composed of strange quark matter (SQM), focusing on finite-size strangelets with baryon number A ≤ 100. Motivated by the emergence of mass–radius outliers in the Gaia DR3 era, we employ a Bayesian exploration of the MIT bag model parameter space, explicitly accounting for finite-size surface and curvature contributions that become relevant at low baryon number. Enforcing the bulk absolute stability requirement for SQM (E/A < 930 MeV), we find that self-gravitating equilibrium sequences are confined to the substellar regime, with typical masses ∼10−6–10−2M⊙ and characteristic radii of order 102–∼103 km. We further show that rapid rotation, treated through a self-consistent framework that incorporates relativistic thermodynamics, can substantially inflate the equatorial radius and extend the accessible mass–radius domain. Although rotation does not eliminate the intrinsic high-density compactness of these configurations, it shifts the most extended models closer to the observational parameter space of massive exoplanets. A comparison with objects from the NASA Exoplanet Archive reveals a pronounced density gap separating standard atomic-matter planets and brown dwarfs from the strangelet-rich branch predicted here. We conclude that light strangelets cannot account for solar-mass white dwarfs, but they robustly predict a previously unexplored population of highly compact substellar objects, offering testable targets for future microlensing searches and high-cadence photometric surveys.

The Curious Case of Dark Faculae on M Dwarf Stars

2026-08-20T23:00:00Z

The study of exoplanet atmospheres has brought a renewed interest in stellar astrophysics. Specifically, stellar magnetic activity from the host star contaminates exoplanet atmosphere transmission spectra, as evidenced by observations from the James Webb Space Telescope. Stellar surface magnetic features in the form of dark spots caused by large concentrations of surface magnetic fields and the more diffuse, extended faculae caused by small-scale magnetic field concentrations change the apparent size of the star in a wavelength-dependent way. These spot and faculae contributions to the change in transit depth contaminate the planetary signal. Here, we study the transition from bright faculae on G and K dwarfs to dark faculae on M dwarfs. This dark appearance of faculae is in significant contrast to the conventional picture that faculae are brighter than the quiet star region as they are on the Sun. We use the 3D radiative magnetohydrodynamics code MURaM to simulate faculae and calculate their spectra with the MPS-ATLAS radiative transfer code. We present a qualitative explanation for the transition from bright to dark faculae, attributing it to shallower flux tubes and reduced vertical temperature gradients at the surfaces of M dwarfs relative to the Sun.

The Merger-driven Formation of Classical Low Surface Brightness Galaxies in Romulus25

2026-08-20T23:00:00Z

We use the Romulus25 cosmological simulation volume to study a large sample of late-type gas-rich galaxies with low central surface brightnesses known as classical low surface brightness (LSB) galaxies and compare them to a mass-matched sample of high surface brightness (HSB) galaxies. We find that classical LSB galaxies make up a substantial fraction of the galaxy population, accounting for ∼60% of all central galaxies with 8 ≤ log10(M⋆/M⊙) ≤ 10. In Romulus25, classical LSB galaxies are predominantly formed through major mergers in which the secondary galaxy is corotating and aligned with the primary galaxy’s gas disk and/or has above-average orbital angular momentum at infall. The merger product is a high-spin galaxy in which star formation is spread out and inefficient, allowing the galaxy to build up a large supply of relatively unenriched gas. The star formation rates of LSB galaxies are nearly constant over time, leading to stellar populations that are, on average, slightly older and therefore optically redder than those of similar HSB galaxies. However, because LSB galaxies are diffuse and metal-poor, they have very little internal reddening, causing them to appear bluer than HSB galaxies. We also find that, when compared to the bulges of HSB galaxies, the bulges of LSB galaxies are similar in mass, but are lower surface brightness, redder, and more diffuse on average. Despite these differences, classical LSB galaxies are part of the continuum of the galaxy population in Romulus25, constituting one of many evolutionary paths.

Distribution of Chemically Processed Dust in a Viscously Evolving Protoplanetary Disk: Application to Crystalline Silicates in Comets

Lily Ishizaki, Shogo Tachibana and Shigeru Ida — 2026-08-20T23:00:00Z

Dust particles undergo chemical reactions in protoplanetary disks according to their environments, producing compositional diversity in planetary materials. Extraterrestrial records of irreversible reactions, such as crystallization of amorphous silicates, provide particularly strong constraints on the early evolution of the protosolar disk. In this study, we investigate such irreversible reactions and the spatiotemporal distribution of reacted dust in a viscously evolving disk using Monte Carlo particle-tracking simulations. We extend a predictive formula for the temperature at which irreversible reactions proceed efficiently (“reaction line”), originally developed for steady accretion disks, to viscously expanding disks. The spatiotemporal distribution of reacted dust is governed by the relative locations of the reaction line and the stagnation line, which separates inward and outward advection in the disk. The reaction line moves inward as the disk cools, while the stagnation line moves outward owing to the radial viscous spreading of the disk. When the reaction line lies far inside the stagnation line, the reacted dust remains inside the reaction line. On the other hand, when the reaction line lies near or beyond the stagnation line, the reacted dust located near the stagnation line or between the two lines is transported outward efficiently. It results in a radially broad distribution of reacted dust throughout the disk, including the outer regions where the temperatures remain too low for reactions. We assessed the disk conditions consistent with the crystalline silicates observed in solar system comets and found that the protosolar disk was likely compact, moderately massive, and not strongly turbulent.

The Effect of Element Diffusion and Convective Overshoot on the Red Giant Branch Bump Brightness

Fen Song, Yan Li, Xiang Li, Xiu-Lin Wang, Jun-Dan Nie and Yi Xie — 2026-08-20T23:00:00Z

Because of the discrepancy between theory and observations on the red giant branch bump (RGBB) brightnesses in globular clusters, we investigate the effect of convective overshoot and element diffusion on the RGBB brightness. Overshooting induces deeper internal mixing, causing the hydrogen-burning shell to encounter the chemical composition discontinuity earlier. As a result, the bump occurs earlier, and the RGBB luminosity is fainter. After considering convective rolling cells, Li developed a turbulent convection model (proposed as the κ–ω model). In the model, based on the solutions of two differential equations about turbulent kinetic energy κ and turbulence frequency ω, the convective heat flux and the turbulent mixing diffusivity in the overshooting and convective regions can be obtained. Thus, we adopt the method presented by the κ–ω model to treat convective overshoot. The size of the overshoot region is determined based on the solar-calibrated model. Then, we computed evolutionary tracks of low-mass stars using the overshooting model and the model that considered the effect of convective overshoot and element diffusion, respectively. We use the observational data from Nataf et al. and compare the absolute magnitudes of the observed RGBB in 72 globular clusters with the theoretically predicted RGBB magnitudes from our models. We find that the predicted line with 12 Gyr computed by the model with convective overshoot and element diffusion is in good agreement with observational data. And we conclude that the predicted line with 13 Gyr from the same model provides the best fit to the observational data while [Fe/H] ≤ −1.2.

Unifying Main-sequence Morphologies in Young Open Clusters: Binary Evolution and the Emergence of Bridge-like Populations

2026-08-20T23:00:00Z

Most massive stars reside in binary systems, and binary interactions can profoundly alter the properties of both stellar components. In young open clusters, such interactions can produce multiple main-sequence populations, despite the coeval nature of the stellar population. In this work, we extend our previous studies on the role of binary evolution in shaping main-sequence morphologies by performing a more detailed and systematic analysis. We investigate the progenitor properties of different main-sequence populations from 10 to 100 Myr using detailed binary models computed with MESA, assuming SMC-like metallicity, and initial primary masses of 3–100 M⊙. We provide physical explanations for the features identified in our earlier work. We focus especially on post–Case A mass-transfer systems, which produce a prominent “bridge-like” feature connecting the reddest Be stars and the bluest blue stragglers. We show that the positions of these stars are sensitive to surface helium enrichment and rotation. We further perform quantitative comparisons with observed clusters aged 30–90 Myr whose turn-off masses are from approximately 9 to 5 M⊙. We find that our models broadly reproduce the observed stellar distributions. However, we underpredict the fraction of Be stars, suggesting that a larger fraction of binaries may undergo stable mass transfer. We also overpredict the number of stars on the redder side of the unresolved-binary sequence, indicating that the initial mass-ratio distribution may deviate from a flat distribution. Overall, this work provides a comprehensive analysis of how binary evolution produces diverse main-sequence populations and lays the foundation for future population-synthesis studies.

Predicting the Kinematics of the Cold Circumgalactic Medium from its Morphology Using Convolutional Neural Networks

2026-08-20T23:00:00Z

We present a novel approach to predicting plane-of-sky velocities of cold gas clouds in the circumgalactic medium (CGM) of galaxies. The method uses a convolutional neural network (CNN) trained on simulated emission maps derived from the TNG50 cosmological simulation, with forward modeled noise properties consistent with upcoming observational facilities. Using 182 Milky Way/Andromeda analog galaxies, we generate emission maps in Hα using Cloudy models, as well as line-of-sight averaged 2D velocity maps. Using a UNet architecture, we train the CNN to take emission maps as input and return plane-of-sky velocity maps as output, which cannot be observationally constrained using traditional methods. Qualitatively, the model is generally able to infer the true overall flow direction. We quantify the effects of Gaussian noise on the network’s training and predictive power. At depths expected to be probed by forthcoming telescopes such as MOTHRA, the network has a typical rms error for the plane-of-sky velocity direction of 0.3−0.5vvir. This implies that 2D emission maps of sufficient depths will be able to estimate two additional phase space dimensions of cold CGM gas, enabling targeted follow-up and a better understanding of overall CGM flows.

Angular Momentum Evolution from Core to Disk Scales in the Early Phase of Star Formation: Constraints from HH 212, HH 211, and B335

Chin-Fei Lee — 2026-08-20T23:00:00Z

I investigate the angular momentum evolution from core to disk scales in the early phase of star formation using three protostellar systems: HH 212, HH 211, and B335. Observations show that the specific angular momentum follows a power-law dependence at core scales and transitions to an approximately constant value at smaller radii, indicating dynamical collapse in the inner envelope. I model this behavior using the inside-out collapse solution of F. H. Shu and its rotating extension, the Terebey–Shu–Cassen model, including modest magnetic effects through a flattened, magnetized core. I find that the observed angular momentum profiles in all three sources are broadly consistent with an inside-out collapse scenario with approximate conservation of specific angular momentum in the collapsing region. The inferred collapse ages and mass infall rates yield total masses accreted onto the center that are broadly consistent with the central masses derived from kinematics, allowing for a fraction of the material to be ejected by jets and winds. The predicted midplane densities at typical radii, including the effect of magnetic flattening, are also consistent with observational estimates. The three systems exhibit a similar pattern of angular momentum evolution despite large differences in the magnitude of their specific angular momentum. In particular, the small disk in B335 can be naturally explained by its lower initial specific angular momentum, although alternative explanations, such as magnetic braking or different initial conditions, cannot be excluded. These results suggest that inside-out collapse, with modest magnetic modification, provides a plausible first-order description of angular momentum evolution from core to disk scales in the early phase of star formation.

JWST NIRCam Reveals the Largest Known M dwarf Debris Disk Around TWA 10 and New Scattered-light Observations of the TWA 25 Debris Disk

2026-08-20T23:00:00Z

We present JWST NIRCam observations of two M dwarf systems located in the TW Hydra association, TWA 10 and TWA 25. Both systems harbor detected debris disks in the F200W and F444W filters. Whereas the TWA 25 disk has been previously imaged, these observations represent the discovery and first images of the TWA 10 disk. In addition to planet searches within these systems, we also conduct an analysis of each debris disk, where the TWA 10 debris disk is characterized for the first time. We find that the TWA 10 debris disk is very large, with a radius of ∼191 au, significantly greater than other known M dwarf debris disks. The TWA 25 disk hosts a sharp inner dust surface density power law and a moderate brightness asymmetry present at 2 μm, suggesting potential sculpting from inner planets and potentially enhanced collisional activity. Finally, we find one potential companion candidate within the TWA 10 system and two within the TWA 25 system, although the measured F200W − F444W color suggests that these candidates are likely background objects. Both systems do not have measured IR-excesses in their SEDs, where radiative-transfer modeling suggests that these disks (and potentially more M dwarf disks) were likely missed by previous disk detection surveys due to having low luminosity fractions.

The Origin of Da Scaling: Suppressed Cooling in Fast-cooling Mixing Layers

Lachlan Lancaster, Drummond Fielding, Rajsekhar Mohapatra and Greg L. Bryan — 2026-08-20T23:00:00Z

In numerical experiments simulating turbulent radiative mixing layers (TRMLs), it is observed that as the cooling time in the mixed gas, tcool, becomes very short compared to the dynamical time of the turbulence, teddy/tcool ≫ 1, there is a change in the scaling behavior of the total energy radiated in the TRML as a function of this ratio, also known as the Damköhler number, Da ≡ teddy/tcool, from to . The latter, so-called “fast-cooling,” regime is of particular interest, as many astrophysical mixing layers lie in this regime. We demonstrate that the origin of this change is the suppression of turbulent folding of the surface by the ram-pressure of the inflowing gas, which becomes much greater than the turbulent pressure in this regime. We present an argument that reproduces the behavior by appealing to the suppression of the fractal structure of the interface by the ram-pressure of the inflowing gas.

Ion “Smoke-ring” Pitch-angle Distributions Measured by the Cassini/MIMI/INCA Instrument Upstream of a Transient Interplanetary Shock at 8.6 au

J. Giacalone, R. B. Decker, M. E. Hill, D. G. Mitchell and C. Paranicas — 2026-08-20T23:00:00Z

On 2003 October 8, the NASA/Cassini spacecraft encountered a transient interplanetary shock at 17:12 UT when the spacecraft was in the ecliptic plane and 8.6 au from the Sun. During a ∼1 hr period prior to the shock passage, ∼3–220 keV (mostly) proton distributions measured by the MIMI/INCA instrument were observed to increase in intensity, peaking near the shock, suggesting it was the accelerator of these particles. The angle between the shock normal and magnetic field was estimated to be 83°, making this a quasi-perpendicular shock. Moreover, ring-like pitch angle distributions (PADs) were observed upstream of the shock during the rise in energetic particle intensity. Peak intensities of the PADs were directed away from the shock along the upstream magnetic field, with ring maxima for intermediate ion energies at pitch angles ∼30°. We present an interpretation of these observations using a combination of theoretical modeling and test-particle orbit-tracing simulations. Our model reproduces the energy and angular dependencies of the low-energy ion data. This observation reveals that quasi-perpendicular shocks can both accelerate particles efficiently and have associated pitch-angle anisotropies confined to near the shock.

Tidal Stream Impact Driving Evolution of the Tilted Accretion Disk in Her X-1

Alexander Bielicki and John M. Blondin — 2026-08-20T23:00:00Z

Hercules X-1 is an X-ray binary system in which a neutron star is accreting matter from a close companion star through Roche lobe overflow. The observed 35-day periodicity in the X-ray light curve has been interpreted as the result of a precessing, tilted accretion disk. We use 3D hydrodynamic simulations to explore the dynamics of the tilted accretion disk and the interaction of the tidal stream with the disk. We find that, in the absence of a tidal stream, the tilted disk remains flat and precesses at a rate given by tidally driven precession. The disk tilt angle remains roughly constant with a slight orbital dependence. In the presence of the mass transfer tidal stream the disk tilt decreases over the course of several binary orbits, with a strong orbital modulation caused by the stream hitting the disk face or outer edge at different orbital phases relative to the disk tilt.

Atmospheric Escape Rates of Planets in Stellar Tidal Fields from 3D Hydrodynamic Simulations

Ritika Sethi, Morgan MacLeod and Sarah Millholland — 2026-08-20T23:00:00Z

Thermally driven atmospheric escape, including photoevaporation and core-powered mass loss, plays a key role in shaping the evolution of close-in exoplanets, yet most current models rely on simplified one-dimensional (1D) descriptions of atmospheric escape. In this work, we perform 3D hydrodynamic simulations of atmospheric outflows from a Jupiter-sized planet embedded in the gravitational potential of a solar-type host star, and compare these results with 1D models to identify the regimes where they perform well and where they break down. We explore a range of configurations by varying the degree of Roche-lobe filling and the thermal state of the outflow. We find that systems with weak tidal influence and high-temperature winds produce nearly spherical and isotropic outflows, whereas more Roche-lobe-filling and cooler winds develop strong anisotropy and form two-tailed structures. We show that the commonly used 1D Parker wind model performs well only in the weak-tides regime, while including tidal corrections yields reasonable estimates of mass-loss rates and captures the mean radial density profile across all regimes, but fails to reproduce the intrinsically three-dimensional, angle-dependent nature of the flow as the outflow transitions from spherical to tidally structured tails. Motivated by these results, we develop a physically informed Mixture Model, calibrated using our 3D simulations, that accurately predicts mass-loss rates across the parameter space explored and outperforms the 1D model with tidal corrections.

Ionized Gas and Merger-triggered Star Formation in the Galaxy NGC 1222

Irina S. Proshina, Dmitriy V. Oparin and Arina Arshinova — 2026-08-20T23:00:00Z

We obtained narrowband images in the emission lines Hα, [N II]λ6583, and [O III]λ5007 at the 2.5 m telescope of the Caucasus Mountain Observatory (CMO) of the Sternberg Astronomical Institute of the Moscow State University with photometer MaNGaL, which showed that the ionized gas in the galaxy NGC 1222 resides in a restricted area of the central part of the host galaxy near to the eastern companion and in the companion to the south-southwest of it. There are star-forming regions there that ionize the gas. Also, we obtained long-slit spectra at the 6 m Big Telescope Alt-azimuthal of the Special Astrophysical Observatory of the Russian Academy of Sciences in two position angles crossing most of the star-forming regions. We derived line-of-sight velocity curves for different components of the ionized gas and revealed kinematic features in the positions of impact of companions, which confirm their accretion origin. We applied several methods for estimating the oxygen abundance in the gas and found differences in the metallicity of the gas in the companion to the south-southwest, in the star-forming regions in the central part of NGC 1222, and presumably in the surrounding gas. Since current star formation is observed only in a restricted central area of NGC 1222 near the eastern companion, as well as in the south-southwestern companion and along its fall trajectory, we conclude that local star formation in the extensive low-metallicity gas disk of neutral hydrogen was triggered by a merger about 6 Myr ago.

Global Multi-ion Solar Wind Model. I. Ion Temperatures

Bart van der Holst, Judit Szente and Enrico Landi — 2026-08-20T23:00:00Z

Over the past several decades, observations have shown that minor ions have a higher temperature and flow faster than protons in the solar wind. Theories based on turbulence have been developed that can explain many of these observed phenomena. We present our first step in developing a global multi-ion solar wind model with turbulence by including ion temperatures but not yet including differential streaming. The extent of this model is from the lower transition region (50,000 K temperature) to the corona and inner heliosphere. It uses low-frequency, reflection-driven incompressible turbulence to address coronal heating and solar wind acceleration. The energy partitioning of the dissipation of turbulence to the electrons and various ions is based on stochastic heating and linear Landau and transit-time damping. In order to test the validity of our approach we have carried out a three-dimensional simulation of the solar corona and the solar wind using an idealized dipole magnetic field configuration, calculated the oxygen temperature across the entire domain, and compared it to measurements obtained from the UltraViolet Coronagraph Spectrometer (UVCS) on the Solar and Heliospheric Observatory (SOHO) satellite and with the Solar Wind Ion Composition Spectrometer (SWICS) on board Advanced Composition Explorer (ACE). The comparison shows that even with the simplified magnetic field configuration the multi-ion model predictions reproduce the phenomenon of preferential heating of heavy ions in both remote-sensing and in situ observations.