Sazuna/UAT_keywords huggingface dataset:
131 and 304 Å Emission Variability Increases Hours Prior to Solar Flare Onset. Thermal changes in coronal loops are well studied, both in quiescent active regions and in flaring scenarios. However, relatively little attention has been paid to loop emission in the hours before the onset of a solar flare; here, we present the findings of a study of over 50 off-limb flares of Geostationary Operational Environmental Satellite class C5.0 and above. We investigated the integrated emission variability for Solar Dynamics Observatory Atmospheric Imaging Assembly channels 131, 171, 193, and 304 Å for 6 hr before each flare and compared these quantities to the same time range and channels above active regions without proximal flaring. We find significantly increased emission variability in the 2–3 hr before flare onset, particularly for the 131 and 304 channels. This finding suggests a potential new flare prediction methodology. The emission trends between the channels are not consistently well correlated, suggesting a somewhat chaotic thermal environment within the coronal portion of the loops that disturbs the commonly observed heating and cooling cycles of quiescent active region loops. We present our approach and the resulting statistics and discuss the implications for heating sources in these preflaring active regions.

Keywords: Solar flares, Solar coronal loops, Solar physics, Solar corona, Solar coronal mass ejections, Active solar corona
On the Geometry of the Near-core Magnetic Field in Massive Stars. It is well-known that the cores of massive stars sustain a stellar dynamo with a complex magnetic field configuration. However, the same cannot be said for the field's strength and geometry at the convective–radiative boundary, which are crucial when performing asteroseismic inference. In this Letter, we present 3D magnetohydrodynamic (MHD) simulations of a 7 M⊙ mid-main-sequence star, with particular attention given to the convective–radiative boundary in the near-core region. Our simulations reveal that the toroidal magnetic field is significantly stronger than the poloidal field in this region, contrary to recent assumptions. Moreover, the rotational shear layer, also important for asteroseismic inference, is specifically confined within the extent of the Brunt–Väisälä frequency peak. These results, which are based on the inferred properties of HD 43317, have widespread implications for asteroseismic studies of rotation, mixing, and magnetism in stars. While we expect our results to be broadly applicable across stars with similar Brunt–Väisälä frequency profiles and stellar masses, we also expect the MHD parameters (e.g., Rem) and the initial stellar rotation rate to impact the geometry of the field and differential rotation at the convective–radiative interface.

Keywords: Stellar magnetic fields, Intermediate-type stars, Magnetohydrodynamical simulations
A Tale of Three: Magnetic Fields along the Orion Integral-shaped Filament as Revealed by the JCMT BISTRO Survey. As part of the B-fields In Star-forming Region Observations survey, we present James Clerk Maxwell Telescope (JCMT) 850 μm polarimetric observations toward the Orion integral-shaped filament (ISF) that covers three portions known as OMC-1, OMC-2, and OMC-3. The magnetic field threading the ISF seen in the JCMT POL-2 map appears as a tale of three: pinched for OMC-1, twisted for OMC-2, and nearly uniform for OMC-3. A multiscale analysis shows that the magnetic field structure in OMC-3 is very consistent at all the scales, whereas the field structure in OMC-2 shows no correlation across different scales. In OMC-1, the field retains its mean orientation from large to small scales but shows some deviations at small scales. Histograms of relative orientations between the magnetic field and filaments reveal a bimodal distribution for OMC-1, a relatively random distribution for OMC-2, and a distribution with a predominant peak at 90∘ for OMC-3. Furthermore, the magnetic fields in OMC-1 and OMC-3 both appear to be aligned perpendicular to the fibers, which are denser structures within the filament, but the field in OMC-2 is aligned along with the fibers. All these suggest that gravity, turbulence, and magnetic field are each playing a leading role in OMC-1, 2, and 3, respectively. While OMC-2 and 3 have almost the same gas mass, density, and nonthermal velocity dispersion, there are on average younger and fewer young stellar objects in OMC-3, providing evidence that a stronger magnetic field will induce slower and less efficient star formation in molecular clouds.

Keywords: Interstellar magnetic fields, Star formation, Interstellar clouds, Polarimetry
Atmospheric Abundances and Bulk Properties of the Binary Brown Dwarf Gliese 229Bab from JWST/MIRI Spectroscopy. We present JWST/Mid Infrared Instrument (MIRI) low-resolution spectroscopy (4.75–14 μm) of the first known substellar companion, Gliese 229Bab, which was recently resolved into a tight binary brown dwarf. Previous atmospheric retrieval studies modeling Gliese 229B as a single brown dwarf have reported anomalously high carbon-to-oxygen ratios (C/O) of ≈1.1 using 1–5 μm ground-based spectra. Here, we fit the MIRI spectrum of Gliese 229Bab with a two-component binary model using the Sonora Elf Owl grid and additionally account for the observed K-band flux ratio of the binary brown dwarf. Assuming the two brown dwarfs share the same abundances, we obtain C/O = 0.65 ± 0.05 and   as their abundances (2σ statistical errors), which are fully consistent with the host star abundances. We also recover the same abundances if we fit the MIRI spectrum with a single brown dwarf model, indicating that binarity does not strongly affect inferred abundances from mid-infrared data when the Teff are similar between components of the binary. In addition, we measure   K and   K for the two brown dwarfs. We find that the vertical diffusion coefficients of   are identical between the two brown dwarfs and in line with   values inferred for isolated brown dwarfs of similar Teff. Our results demonstrate the power of mid-infrared spectroscopy in providing robust atmospheric abundance measurements for brown dwarf companions and, by extension, giant planets.

Keywords: High contrast spectroscopy, Atmospheric composition, Brown dwarfs, T dwarfs
Tracing Back a Second-generation Star Stripped from Terzan 5 by the Galactic Bar. The Galactic bulge hosts the Milky Way's oldest stars, possibly coming from disrupted globular clusters (GCs) or the bulge's primordial building blocks, making these stars witnesses to the Galaxy's early chemical enrichment. The Galactic bar currently dominates the bulge's region, altering the orbits of objects formed before its formation and complicating the trace of the field stars' original clusters. Here, we present the discovery of a fossil record of this evolution, SOS1—a star trapped in the bar, exhibiting significant enhancements in nitrogen, sodium, and aluminum, typical of second-generation GC stars. SOS1 also shows an s-process Ce enhancement, suggesting an old age and early enrichment by fast-rotating massive stars in the Galaxy's earliest phases. With the purpose of finding the SOS1's parent GC, we derive its precise chemodynamical properties by combining high-precision proper motions from Gaia with Apache Point Observatory Galactic Evolution Experiment–detailed chemical abundances. Our analysis suggests that SOS1 was possibly stripped from the GC Terzan 5 by the Galactic bar's gravitational influence approximately 350 Myr ago. We also found chemical similarities suggesting that SOS1 belonged to the most metal-poor, ancient, and peripheral stellar population of Terzan 5. These results not only support the hypothesis that Terzan 5 is a remnant of a primordial building block of the Galactic bulge but also suggest this cluster continues losing stars to the bar. Our method highlights how powerful the use of chemodynamical properties in the Gaia era is for tracing the Galaxy's evolutionary history.

Keywords: Globular star clusters, Galactic archaeology, Milky Way dynamics, Galaxy abundances, Galactic bar
The XRISM/Resolve View of the Fe K Region of Cyg X-3. The X-ray binary system Cygnus X-3 (4U 2030+40, V1521 Cyg) is luminous but enigmatic owing to the high intervening absorption. High-resolution X-ray spectroscopy uniquely probes the dynamics of the photoionized gas in the system. In this Letter, we report on an observation of Cyg X-3 with the XRISM/Resolve spectrometer, which provides unprecedented spectral resolution and sensitivity in the 2–10 keV band. We detect multiple kinematic and ionization components in absorption and emission whose superposition leads to complex line profiles, including strong P Cygni profiles on resonance lines. The prominent Fe XXV Heα and Fe XXVI Lyα emission complexes are clearly resolved into their characteristic fine-structure transitions. Self-consistent photoionization modeling allows us to disentangle the absorption and emission components and measure the Doppler velocity of these components as a function of binary orbital phase. We find a significantly higher velocity amplitude for the emission lines than for the absorption lines. The absorption lines generally appear blueshifted by ∼‑500–600 km s‑1. We show that the wind decomposes naturally into a relatively smooth and large-scale component, perhaps associated with the background wind itself, plus a turbulent, denser structure located close to the compact object in its orbit.

Keywords: High resolution spectroscopy, High mass x-ray binary stars
A New View of the Spiral Structure of the Northern Outer Milky Way in Carbon Monoxide. Based on 32,162 molecular clouds from the Milky Way Imaging Scroll Painting project, we obtain new face-on molecular gas maps of the northern outer Galaxy. The total molecular gas surface density map reveals three segments of spirals, extending 16–43 kpc in length. The Perseus and Outer arms stand out prominently, appearing as quasi-continuous structures along most of their length. At the Galactic outskirts, about 1306 clouds connect the two segments of the new spiral arm discovered by T. M. Dame &amp; P. Thaddeus (2011) in the first quadrant and Y. Sun et al. in the second quadrant, possibly extending the arm into the outer third quadrant. Logarithmic spirals can be fitted to the CO arm segments with pitch angles ranging from 4∘ to 12∘. These CO arms extend beyond previous CO studies and the optical radius, reaching a Galactic radius of about 22 kpc, comparable to the H I radial range.

Keywords: Spiral galaxies, Molecular clouds, Spiral arms, Milky Way disk, CO line emission, Spiral pitch angle
Detailed Study of Stars and Gas in a z = 8.3 Massive Merger with Extreme Dust Conditions. We present galaxy MACS0416-Y1 at zspec = 8.312 as observed by the CAnadian NIRISS Unbiased Cluster Survey. MACS0416-Y1 has been shown to have extreme dust properties; thus, we study the physical properties and star formation histories of its resolved components. Overall, we find that MACS0416-Y1 is undergoing a star formation burst in three resolved clumps. The central clump is less massive compared to the other clumps and possibly formed in the merging process of the two larger clumps. Although the star formation history indicates an ongoing star formation burst, this gas-rich galaxy shows comparable star formation efficiency to cosmic noon galaxies. Using NIRSpec prism spectroscopy, we measure metallicity,  , ionization parameter,  , and electron temperature Te = 18000 ± 4000 K. The emission line ratios of the galaxy indicate an evolved interstellar medium similar to z ∼ 2 star-forming galaxies. Further, we find possible presence of ionization from an active galactic nucleus (AGN) using emission line diagnostics; however, we do not detect a broad-line component in the Hβ emission line. As this gas-rich galaxy is undergoing a major merger, we hypothesize that the high dust temperature in MACS0416-Y1 is caused by the star formation burst or a possible narrow-line AGN.

Keywords: Strong gravitational lensing, Active galaxies, High-redshift galaxies, Reionization
Millinovae: A New Class of Transient Supersoft X-Ray Sources without a Classical Nova Eruption. Some accreting binary systems containing a white dwarf (such as classical novae or persistent supersoft sources) are seen to emit low-energy X-rays with temperatures of ∼ 106 K and luminosities exceeding 1035 erg s‑1. These X-rays are thought to originate from nuclear burning on the white dwarf surface, either caused by a thermonuclear runaway (classical novae) or a high mass-accretion rate that sustains steady nuclear burning (persistent sources). The discovery of transient supersoft X-rays from ASASSN-16oh challenged these ideas, as no clear signatures of mass ejection indicative of a classical nova eruption were detected, and the origin of these X-rays remains controversial. It was unclear whether this star was one of a kind or representative of a larger, as yet undiscovered, group. Here, we present the discovery of 29 stars located in the direction of the Magellanic Clouds exhibiting long-duration, symmetrical optical outbursts similar to that seen in ASASSN-16oh. We observed one of these objects during an optical outburst and found it to be emitting transient supersoft X-rays, while no signatures of mass ejection (indicative of a classical nova eruption) were detected. We therefore propose that these objects form a homogeneous group of transient supersoft X-ray sources, which we dub "millinovae" because their optical luminosities are approximately a 1000 times fainter than those of ordinary classical novae.

Keywords: Cataclysmic variable stars, Dwarf novae, Classical novae
Potential for Life to Exist and be Detected on Earth-like Planets Orbiting White Dwarfs. With recent observations confirming exoplanets orbiting white dwarfs, there is growing interest in exploring and quantifying the habitability of temperate rocky planets around white dwarfs. In this work, the limits of the habitable zone of an Earth-like planet around a white dwarf are computed based on the incident stellar flux, and these limits are utilized to assess the duration of habitability at a given orbital distance. For a typical 0.6M⊙ white dwarf an Earth-like planet at ∼0.012 au could remain in the temporally evolving habitable zone, maintaining conditions to support life, for nearly 7 Gyr. Also, additional constraints on habitability are studied for the first time by imposing the requirement of receiving sufficient photon fluxes for UV-mediated prebiotic chemistry and photosynthesis. We demonstrate that these thresholds are comfortably exceeded by planets in the habitable zone. The prospects for detecting atmospheric biosignatures are also evaluated and shown to require integration times on the order of 1 hr or less for ongoing space observations with JWST.

Keywords: White dwarf stars, Astrobiology, Habitable zone, Habitable planets
The Shape of the Heliosphere Derived from the IBEX Ribbon. The shape of the heliosphere remains largely uncertain due to the lack of in situ measurements. However, the energetic neutral atom (ENA) ribbon structure discovered by the Interstellar Boundary EXplorer (IBEX) satellite provides a new perspective. The present study reveals that the IBEX ribbon ENA flux, observed over a full solar cycle, correlates well with the solar wind ion flux measured at 1 au after a time delay of a few years. The time lag between the two can be used to estimate the heliopause distance and the heliosphere shape. The results show that the heliopause distance is shortest slightly south of the nose direction (∼100 au) and remains almost constant with the ecliptic longitude. However, the distance extends to ∼800 au toward the polar region, and it seems that there is no broadly symmetrical and elongated single heliospheric tail. While these features are consistent with the "croissant-like" model (no tail, but with two jet-like tail lobes) of the heliosphere, they cannot fully exclude the traditional "comet-like" model with a strong local interstellar medium magnetic field. Additional data and modeling are needed to ascertain the precise shape of the heliosphere.

Keywords: Heliopause, Solar wind, Solar cycle, Heliosphere
Robust Detection of Hot Intragroup Medium in Optically Selected, Poor Galaxy Groups by eROSITA. Over the last several decades, extensive research has been conducted on the baryon cycles within cosmic structures, encompassing a broad mass range from dwarf galaxies to galaxy clusters. However, a notable gap in understanding the cosmic baryon cycle is the poor galaxy groups with halo masses around 1013 M⊙. Poor galaxy groups, like our own Local Group, are prevalent throughout the Universe, yet robust detection of their hot, X-ray-emitting intragroup medium (IGrM) has remained elusive. The presence of this hot IGrM is crucial for addressing the long-standing "missing baryons" problem. Previous ROSAT-based studies were limited by a small number of X-ray bright samples, thus restricting the scope of their findings. Here, we show a robust detection of this hot IGrM in a large, optically selected poor groups sample, based on the stacked X-ray images from the eROSITA Final Equatorial Depth Survey. These groups are identified in DESI Legacy Survey with a mass range of log(Mhalo/h‑1 M⊙) = 11.5–13.5 and a redshift range of z = 0.1–0.5. Additionally, our results indicate that despite its presence in virtually groups at all sizes, this gas component is still not sufficient to recover the universal baryon fraction, and hence the "missing baryons" problem still persists in poor galaxy groups.

Keywords: X-ray astronomy, Hot intergalactic medium, Galaxy groups, Missing mass
Double "acct": A Distinct Double-peaked Supernova Matching Pulsational Pair Instability Models. We present multiwavelength data of SN 2020acct, a double-peaked stripped-envelope supernova (SN) in NGC 2981 at ∼150 Mpc. The two peaks are temporally distinct, with maxima separated by 58 rest-frame days and a factor of 20 reduction in flux between. The first is luminous (Mr = ‑18.00 ± 0.02 mag) and blue (g ‑ r = 0.27 ± 0.03 mag) and displays spectroscopic signatures of interaction with hydrogen-free circumstellar material. The second peak is fainter (Mr = ‑17.29 ± 0.03 mag) and has some spectroscopic similarities to an evolved stripped-envelope SN, with strong forbidden [Ca II] and [O II] features. No other known double-peaked SN exhibits a light curve similar to that of SN 2020acct. We find the likelihood of two individual SNe occurring in the same star-forming region within that time to be highly improbable, while an implausibly fine-tuned configuration would be required to produce two SNe from a single binary system. We find that the peculiar properties of SN 2020acct match models of pulsational pair instability (PPI), in which the initial peak is produced by collisions of shells of ejected material, shortly followed by core collapse. Pulsations from a star with a 72 M⊙ helium core provide an excellent match to the double-peaked light curve. The local galactic environment has a metallicity of 0.4 Z⊙, a level where massive single stars are not expected to retain enough mass to encounter the PPI. However, late binary mergers or a low-metallicity pocket may allow the required core mass. We measure the rate of SN 2020acct–like events to be &lt;3.3 × 10‑8 Mpc‑3 yr‑1 at z = 0.07, or &lt;0.1% of the total core-collapse SN rate.

Keywords: Type Ib supernovae, Massive stars, Supernovae, Core-collapse supernovae
Can Slow Pulsars in Milky Way Globular Clusters Form via Partial Recycling?. Alongside the population of several hundred radio millisecond pulsars currently known in Milky Way globular clusters, a subset of six slowly spinning pulsars (spin periods 0.3–4 s) are also observed. With inferred magnetic fields ≳1011 G and characteristic ages ≲108 yr, explaining the formation of these apparently young pulsars in old stellar populations poses a major challenge. One popular explanation is that these objects are not actually young but instead have been partially spun up via accretion from a binary companion. In this scenario, accretion in a typical low-mass X-ray binary (LMXB) is interrupted by a dynamical encounter with a neighboring object in the cluster. Instead of complete spin-up to millisecond spin periods, the accretion is halted prematurely, leaving behind a "partially recycled" neutron star. In this Letter, we use a combination of analytic arguments motivated by LMXB evolution and N-body simulations to show that this partial recycling mechanism is not viable. Realistic globular clusters are not sufficiently dense to interrupt mass transfer on the short timescales required to achieve such slow spin periods. We argue that collapse of massive white dwarfs and/or neutron star collisions are more promising ways to form slow pulsars in old globular clusters.

Keywords: Globular star clusters, Millisecond pulsars, Low-mass x-ray binary stars, N-body simulations, Radio pulsars
Energy Dissipation in Strong Collisionless Shocks: The Crucial Role of Ion-to-electron Scale Separation in Particle-in-cell Simulations. Energy dissipation in collisionless shocks is a key mechanism in various astrophysical environments. Its nonlinear nature complicates analytical understanding and necessitates particle-in-cell (PIC) simulations. This study examines the impact of reducing the ion-to-electron mass ratio (mr), to decrease computational cost, on energy partitioning in one spatial and three velocity-space dimension PIC simulations of strong, nonrelativistic, parallel electron–ion collisionless shocks using the SHARP code. We compare simulations with a reduced mass ratio (mr = 100) to those with a realistic mass ratio (mr = 1836) for shocks with high ( ) and low ( ) Alfvén Mach numbers. Our findings show that the mass ratio significantly affects particle acceleration and thermal energy dissipation. At high  , a reduced mass ratio leads to more efficient electron acceleration and an unrealistically high ion flux at higher momentum. At low  , it causes complete suppression of electron acceleration, whereas the realistic mass ratio enables efficient electron acceleration. The reduced mass ratio also results in excessive electron heating and lower heating in downstream ions at both Mach numbers, with slightly more magnetic field amplification at low  . Consequently, the electron-to-ion temperature ratio is high at low   due to reduced ion heating and remains high at high   due to increased electron heating. In contrast, simulations with the realistic mr show that the ion-to-electron temperature ratio is independent of the upstream magnetic field, a result not observed in reduced mr simulations.

Keywords: Galaxy clusters, Planetary bow shocks, Stellar bow shocks, Supernova remnants, Shocks