Sazuna/UAT_keywords huggingface dataset:
The SPHINX M Dwarf Spectral Grid. II. New Model Atmospheres and Spectra to Derive the Fundamental Properties of Mid-to-late Type M Dwarfs. M dwarfs are the most dominant stars in the Galaxy. Their interiors and atmospheres exhibit complex processes including dust condensation, convective feedback, and magnetic activity-driven heterogeneity. Standard stellar characterization methods often struggle to capture these coupled effects. Paper I of this series introduced SPHINX I, a validated grid of self-consistent radiative-convective model atmospheres and spectra for M dwarfs with up-to-date molecular opacities suitable for early-to-mid M dwarfs. Here, we present SPHINX II, which extends the model grid to cover mid-to-late type M dwarfs, including both gray and physically motivated condensate cloud treatments and shorter convective mixing lengths. We validate SPHINX II using 39 benchmark FGK+M binary systems observed with SpeX/IRTF and apply it to 32 mid-to-late type M dwarfs from the SpeX Prism Library. SPHINX II yields improved fits that are statistically consistent with empirical benchmarks, achieving precisions of 0.078 dex in metallicity and 0.13 dex in C/O. Across the model grid, condensate cloud mass peaks between 2100 and 2400 K, decreasing sharply toward both cooler and hotter temperatures. We find the onset of the cloud-free regime around ∼2900 K, and below 2100 K, we see the formation of deep/buried clouds. As a case study, we also model Trappist-1 and show that even mass-limited silicate grains subtly modify its emergent spectrum, suppressing near-infrared flux and reddening the mid-infrared slope via shallow cloud formation near 10−2 bar. In sum, SPHINX II provides an improved framework for constraining the fundamental properties of mid-to-late M dwarfs.

Keywords: M dwarf stars, Bayesian statistics, Theoretical models, Atmospheric clouds, Atmospheric composition
Modeling of Collisional Outcomes Based on Impact Simulations of Mars-sized Bodies. We investigate the outcomes of collisions between Mars-sized bodies through smooth particle hydrodynamics simulations, focusing on the transitions among merging, hit-and-run, and catastrophic disruption. By systematically varying impact velocity, angle, and mass ratio, we characterize the dependence of collision outcomes on geometric and energetic parameters. A new analytic model is developed using characteristic energies—particularly the energy deposited in overlapping regions of the colliding bodies—to accurately describe the mass of the largest and second largest remnants. The model successfully reproduces simulation results across a broad range of impact conditions and improves on previous models by better capturing the transitions between merging, hit-and-run, and disruption. We also derive outcome formulas averaged over impact-parameter-weighted angular distributions, enabling more realistic applications to integrated modeling of planet formation. The model further shows consistency with outcomes from dust aggregate collision simulations, highlighting its utility for modeling collisional processes not only for large planetesimals but also for smaller bodies.

Keywords: Collisional processes, Planet formation, Planetary science
Fast-cooling Synchrotron Prompt Emission from Internal Shocks in GRB 241030A. We present a time-resolved joint Swift─Fermi spectral study of GRB 241030A (z = 1.411) that cleanly isolates the synchrotron origin of its prompt emission and favors a matter-dominated internal-shock scenario. The light curve shows two episodes separated by a quiescent gap. Episode 1 (0─45 s) is well described by a single power law with photon index ≃ ─3/2, consistent with the fast-cooling synchrotron slope below the peak. Episode 2 (100─200 s) exhibits two robust spectral breaks: a low-energy break at Eb ∼ 2─3 keV that remains nearly constant in time, and a spectral peak Ep that tracks the flux within pulses but steps down between them. The photon indices below and above Eb cluster around −2/3 and −3/2, respectively, as expected for fast-cooling synchrotron emission. The burst displays an unusually small (consistent with zero) spectral lag across Fermi Gamma-ray Burst Monitor bands. At later times (≳230 s), the spectrum softens toward ∼─2.7, as expected when the observing band lies above both νm and νc. These behaviors are difficult to reconcile with a globally magnetized outflow with a decaying field, which naturally produces hard-to-soft Ep evolution, growing νc, and appreciable lags. By contrast, internal shocks with a roughly steady effective magnetic field and a time-variable minimum electron Lorentz factor (equivalently, for example, a varying fraction of accelerated electrons) simultaneously account for: (1) the stable Eb; (2) the intensity-tracking yet stepped-down Ep; (3) the canonical −2/3 and −3/2 slopes; and (4) the near-zero lag.

Keywords: Gamma-ray bursts, High energy astrophysics
Galaxy Evolution in Compact Groups. III. Structural Analysis of Galaxies and Dynamical State of Non-isolated Compact Groups. Compact groups (CGs) of galaxies are dense systems where projected separations are comparable to their optical diameters. A subset—non-isolated CGs—are embedded within major structures. Using multiband S-PLUS data, we analyse galaxies in 122 non-isolated CGs within more-massive systems, such as larger groups and clusters. We compare them to galaxies in the host structures, hereafter surrounding group galaxies. Structural parameters were obtained with MorphoPLUS, a pipeline for multiwavelength Sérsic profile fitting. Dividing galaxies into early-type galaxies (ETGs), transition, or late-types (LTGs), we find the following: (1) Non-isolated CGs host higher quenched fractions and more ETGs, especially for stellar masses  log(M/M⊙)&gt;10.2  than surrounding groups. (2) Sérsic indices increase with wavelength for all morphological types in both environments, whereas effective radii show a stronger morphology-dependent behavior—ETGs become more compact towards redder bands, while LTGs exhibit flatter Re(λ) trends. Environmental differences remain weak, with only a modest enhancement of the gradients for ETGs in non-isolated CGs. (3) Transition galaxies in CGs show a concentrated Re─n distribution and faint-end bimodality, consistent with ongoing morphological transformation absent in surrounding groups. (4) Phase-space analysis indicates that some CGs in clusters are projection artifacts, while others are genuine dense systems at various infall stages, from recent arrivals to ancient remnants. These results show that galaxies in non-isolated CGs follow distinct evolutionary paths compared to their surrounding groups galaxies, suggesting that the compact configuration plays a unique role beyond the influence of the larger-scale environment.

Keywords: Galaxy evolution, Galaxy interactions, Galaxy groups, Galaxy environments
Cascade Processes of Strong and Weak Relativistic Magnetohydrodynamic Turbulence. On the framework of relativistic force-free magnetohydrodynamic (MHD) turbulence, we explore the fundamental properties of strong and weak turbulent cascades using high-resolution numerical simulations in the presence of a uniform background magnetic field. We find that (1) power spectra and scale-dependent anisotropies both for the strong and weak turbulence resemble those observed in the nonrelativistic MHD turbulence; (2) intermittency of magnetic fields in strong turbulence is stronger than that in the weak one; (3) generated Alfvén modes show similar energy spectra and scale-dependent anisotropies to those of nonrelativistic case; (4) generated fast modes present a power spectrum similar to that of Alfvén modes, with a strong (for strong turbulence) or weak (for weak turbulence) scale-dependent anisotropy, which are significantly different from nonrelativistic turbulence; and (5) applications of our numerical results to neutron star magnetospheres show that the strong (or moderately weak) turbulent cascade can explain the X-ray radiation of the Vela pulsar. Our study is of great significance for understanding energy transfer, magnetic field evolution, and particle acceleration mechanisms in extreme astrophysical environments.

Keywords: Interplanetary turbulence, Magnetohydrodynamics, Relativistic fluid dynamics
No Sign of a Magnetar Remnant Following the Kilonova-producing Long GRB 211211A ∼1.7 yr Later. In addition to a gamma-ray burst (GRB), the merger of two neutron stars (NSs) may produce a temporarily or indefinitely stable NS remnant with a strong magnetic field (a "magnetar"). As this magnetar remnant spins down, it can deposit its rotational energy into the surrounding kilonova ejecta, producing synchrotron emission that peaks in the radio bands ∼months to years after the merger ("boosted kilonova"). The nearby (z = 0.0763) long-duration GRB 211211A, which has an apparent kilonova counterpart and likely NS merger progenitor, may have produced such a remnant. We observed the location of GRB 211211A at 6 GHz with the NSF's Karl G. Jansky Very Large Array (VLA) spanning ≍0.54─1.7 yr after the burst. We do not detect any radio emission, placing strong limits on the energy deposited into the ejecta by any remnant to ≲4.4 × 1052 erg. Due to the proximity of the event, we are also able to place limits on a kilonova afterglow that did not receive any additional energy deposition, though it is possible such emission will be suppressed until ∼4 yr after the burst, when the kilonova is expected to overtake the forward shock of the GRB. Future observations with the VLA and next-generation radio facilities will be able to further constrain the magnetar-boosted kilonova and kilonova-afterglow scenarios, as well as directly constrain models in the scenario that GRB 211211A was instead produced by a collapsar.

Keywords: Neutron stars, Magnetars, Gamma-ray bursts, High energy astrophysics
Gamma-Ray Orbital Modulation in Spider Pulsars: Three Discoveries and a Universal Modulated Fraction. Compact binary millisecond pulsars (also known as spiders) allow us to probe pulsar winds in their innermost regions, between the light cylinder (radius ∼107 cm) and the companion star (at ∼1011 cm). Their flux is known to vary along the orbit, from radio to X-rays. During the past decade, gamma-ray orbital modulation (GOM) has been discovered in a handful of spiders, but its origin remains largely unknown. We present the results of a systematic search for GOM among 43 systems, selecting pulsed 0.1─1 GeV photons and using spin and orbital ephemeris from Fermi's Third Pulsar Catalog. We discover GOM from three spiders—PSR J1124-3653, PSR J1946-5403, and PSR J2215+5135—and confirm four previous detections. In all seven cases so far, the GOM peaks near the pulsar's superior conjunction. The X-ray orbital light curves are usually in antiphase, peaking when the pulsar is at inferior conjunction, but we find one case where both gamma rays and X-rays peak around superior conjunction: PSR J1946-5403. We measure the modulated fractions of the GOM and find consistent values for all seven spiders, with an average 22.0% ± 2.6%. Including eclipsing systems seen edge-on, we find no clear dependence of the modulated fraction on the orbital inclination (within ≃45°─90°). Our results challenge previous models proposed to explain GOM in spiders, based on inverse Compton and synchrotron emission close to the companion, since these predict a clear dependence on orbital inclination (stronger modulation at high inclinations). We nearly double the number of GOM detections in spiders, showing that it is more common than previously thought.

Keywords: Compact binary stars, Gamma-rays, High energy astrophysics, Millisecond pulsars
Modeling the Effect of C/O Ratio on Complex Carbon Chemistry in Cold Molecular Clouds. Elemental abundances, which are often depleted with respect to solar values, are important input parameters for kinetic models of interstellar chemistry. In particular, the amount of carbon relative to oxygen is known to have a strong effect on the modeled abundances of many species. While previous studies have focused on comparison of modeled and observed abundances to constrain the C/O ratio, the effects of this parameter on the underlying chemistry have not been well studied. We investigated the role of the C/O ratio on dark-cloud chemistry using the NAUTILUS code and machine learning techniques for molecular representation. We find that modeled abundances are quite sensitive to the C/O ratio, especially for carbon-rich species such as carbon chains and polycyclic aromatic hydrocarbons. CO and simple ice-phase species are found to be major carbon reservoirs under both oxygen-poor and oxygen-rich conditions. The appearance of C3H4 isomers as significant carbon reservoirs, even under oxygen-rich conditions, indicates the efficiency of gas-phase C3 formation followed by adsorption and grain-surface hydrogenation. Our model is not able to reproduce the observed, gas-phase C/H ratio of TMC-1 CP at the time of best fit with any C/O ratio between 0.1 and 3, suggesting that the modeled freeze-out of carbon-bearing molecules may be too rapid. Future investigations are needed to understand the reactivity of major carbon reservoirs and their conversion to complex organic molecules.

Keywords: Polycyclic aromatic hydrocarbons, Molecular clouds, Chemical abundances, Chemical kinetics, Astrochemistry
The Transport of Angular Momentum for Massive Stars. I. Formation of Slowly Rotating Early-type Nitrogen-sequence Wolf─Rayet Stars. The evolutionary scenario of early-type nitrogen-sequence Wolf─Rayet (WNE) stars predicts a slowly rotating subclass that typically forms after the red supergiant phase. Their slow rotation rates are attributed to stellar winds that remove angular momentum transferred outward during core contraction. We incorporate improved prescriptions for internal gravity waves and the magnetic Tayler instability into single massive star evolution models. Our simulations successfully produce slowly rotating WNE stars and determine optimal parameters for both mechanisms (A ≥ 10 for internal gravity waves, α = 0.01 for the revised Tayler instability). The results demonstrate that the efficiency of angular momentum transfer in massive stars is significantly enhanced compared to low-mass stars; both processes can self-consistently explain the slow rotation of WNE stars, confirming their efficiency in angular momentum redistribution and providing crucial theoretical support for the existence of this predicted stellar population.

Keywords: Stellar interiors, Internal waves, Wolf-Rayet stars, Stellar rotation, Magnetic fields
CHIME/FRB Discovery and Localization of the Swift-observed FRB 20241228A. On 2024 December 28, the Canadian Hydrogen Intensity Mapping Experiment (CHIME) FRB project detected the thus-far nonrepeating FRB 20241228A with a real-time signal-to-noise ratio of &gt;50. Approximately 112 s later, the X-ray Telescope on board the Neil Gehrels Swift Observatory was on-source, the fastest follow-up to date of a nonrepeating fast radio burst (FRB). Using CHIME/FRB and two of the three CHIME/FRB Outriggers, we obtained a very-long-baseline interferometry (VLBI) localization for FRB 20241228A with a 1σ confidence ellipse of 11″ by 0 .″ 2. This represents the first published localization using both the CHIME k'niʔatn k'l⌣stk'masqt and CHIME Green Bank Observatory Outriggers. We associate FRB 20241228A with a star-forming galaxy at a redshift of z = 0.1614 ± 0.0002. The persistent X-ray luminosity limit at this source's location and distance is &lt;1.2 × 1043 erg s−1 in the 0.3−10 keV band, the most stringent limit of any nonrepeating FRB to date. The stellar mass (∼2.6 × 1010 M⊙) and star formation rate (∼2.9 M⊙ yr−1) of the host galaxy of FRB 20241228A are consistent with the broader FRB host-galaxy population. We measure significant scattering (∼1 ms at 600 MHz) and scintillation (∼15 kHz at 600 MHz) along the line of sight to this source, and suggest the scintillation screen is Galactic while the scattering screen is extragalactic. FRB 20241228A represents an exciting example of a new era in which we can harness VLBI localizations and rapid high-energy follow-up to probe FRB progenitors.

Keywords: Very long baseline interferometry, Transient sources, Radio bursts, Radio interferometry, Radio transient sources
SN 2024aecx: A Fast-evolving Type IIb Supernova with a Prominent Shock-cooling Peak. SN 2024aecx is a nearby (∼11 Mpc) Type IIb SN discovered within ∼1 day after explosion. In this paper we report high-cadence photometric (typically 0.5 ∼ 1 day) and spectroscopic follow-up observations, conducted from as early as 0.27 day post discovery out to the nebular phase at 158.4 days. We analyze the environment of SN 2024aecx and derive a new distance (11.3 ± 1.1 Mpc), metallicity and host extinction. The light curve exhibits a hot and luminous shock-cooling peak at the first few days, followed by a main peak with very rapid postmaximum decline. The earliest spectra are blue and featureless, while from 2.3 days after discovery prominent P-Cygni profiles emerge. At nebular phase, the emission lines exhibit asymmetric and double-peaked profiles, indicating asphericity and/or early dust formation in the ejecta. Nebular spectral modelling indicates a blueshifted O-rich clump moving toward observer, and the [O I]/[Ca II] line ratio suggests an intermediate-mass progenitor. We simulated the progenitor and explosion using a two-component model of shock cooling and radioactive 56Ni heating; our model favors an extended, low-mass H-rich envelope with Me = 0.04 ± 0.01 M⊙ and a low ejecta mass of  Mej=1.55−0.14+0.18M⊙ . And the nebular-phase spectra and light-curve modelling both suggest that it most likely originated from an intermediate-mass binary progenitor system. The comprehensive monitoring of SN 2024aecx, coupled with the detailed characterization of its local environment, establishes it as a benchmark event for probing the progenitors and explosion mechanisms of Type IIb SNe.

Keywords: Galaxy distances, Core-collapse supernovae, Light curves, Galaxy abundances, Spectroscopy, Stellar evolution
Low-energy Radio Bursts from Magnetar XTE J1810−197: Implications for Fast Radio Bursts. Magnetars are the leading candidate sources of fast radio bursts (FRBs). However, the observational probes of the connections between magnetars and FRBs are severely limited by the paucity of detection of highly energetic radio events from magnetars—to date, only one radio burst as energetic as FRBs has been detected from a Galactic magnetar. Here, we present a detailed analysis of a large sample of low-energy bursts detected from the magnetar XTE J1810−197, and probe their implications for FRB emission from magnetars. We report detection of over 97,000 bright radio pulses from 242 observations of the magnetar XTE J1810−197 over 4.5 yr and two decades in frequency (300 MHz─6.15 GHz), using the Giant Meterwave Radio Telescope and the Green Bank Telescope, after its recent outburst onset in 2018 December. We present a detailed analysis of the burst fluence distributions and their trends with time as well as frequency, and the waiting time distribution. We show that XTE J1810−197 rapidly switches between pulsar-like and giant-pulse-like emission states, and magnetars like XTE J1810−197 remain viable and likely emitters of FRBs, in the form of giant pulses with energies comparable to FRBs. We also demonstrate that the lack of detection of an underlying periodicity in the bursts from repeating FRBs might be caused by emission across a wide range of spin phases.

Keywords: Radio transient sources, Magnetars, Non-thermal radiation sources, Pulsars
On the Interstellar Extinction Curve toward HD 93222, a Sight Line with an Exceedingly Narrow 2175 Å Extinction Bump. The 2175 Å extinction bump, the most prominent spectral feature superimposed on the interstellar extinction curve, is widely seen in the interstellar medium of the Milky Way and external galaxies, both near and far. While its central wavelength is remarkably stable and independent with environment, its width shows considerable variation and environmental dependence. Here, we examine the extinction curve for the line of sight toward HD 93222, a young star located in the Carina Nebula. It is found that the 2175 Å bump is extremely sharp, which is among the narrowest ever found in the Milky Way and external galaxies. We model the derived extinction curve and find that, to explain the extinction characteristics of HD 93222, in addition to the conventional silicate and graphite dust mixture, an additional population of nano-sized graphitic grains is required.

Keywords: Interstellar dust, Silicate grains, Carbonaceous grains, Interstellar extinction
Carnegie Supernova Project: Fast-declining Type Ia Supernovae as Cosmological Distance Indicators. In this paper, the suitability of fast-declining Type Ia supernovae (SNe Ia) as cosmological standard candles is examined utilizing a "Hubble Flow" sample of 43 of these objects observed by the Carnegie Supernova Project (CSP). We confirm previous suggestions that fast-declining SNe Ia offer a viable method for estimating distances to early-type galaxies when the color-stretch parameter, sBV, is used as a measure of the light-curve shape. As a test, we employ the Tripp method, which models the absolute magnitude at maximum as a function of light-curve shape and color. We calibrate the sample using 12 distance moduli based on published infrared surface-brightness fluctuations to derive a value of the Hubble constant that is in close agreement with the value obtained for the full sample of CSP SNe Ia using the same methodology. We also develop a new and simple method of estimating the distances of fast decliners based only on their colors at maximum (and not light-curve shape) and find that it leads to similar results as with using the Tripp method. This "color" technique is a powerful tool that is unique to fast-declining SNe Ia. We show that the colors of the fast decliners at maximum light are strongly affected by photospheric temperature differences and not solely due to dust extinction, and provide a physical rationale for this effect. *This paper includes data gathered with the 6.5 m Magellan telescopes at Las Campanas Observatory, Chile.

Keywords: Observational cosmology, Type Ia supernovae, Supernovae
Identifying Quasiperiodic Micropulses in Pulsars with FAST Using Convolutional Neural Networks. Quasiperiodic micropulses (QMPs) are quasiperiodic microstructural features manifested in individual pulsar radio pulses, the study of which is crucial for understanding pulsar radiation mechanisms. Manual identification of QMPs in large-scale pulsar single-pulse datasets remains highly inefficient. To address this, we propose a dual-stage residual network (DSR) that achieves automated QMP detection in Five-hundred-meter Aperture Spherical radio Telescope observational data through joint analysis of single-pulse profiles and their amplitude distribution profiles, defined as the power spectra of the autocorrelation function derivatives of the microstructure residuals. The model was trained on PSR B1933+16 data from 2019 (10,486 single pulses) and evaluated on manually annotated PSR B1933+16 data from 2020 (9657 single pulses). DSR achieved 96.10% recall and 95.85% precision on the test set. This approach provides an automated pipeline for large-scale, reproducible QMP identification and establishes the foundation for in-depth investigation of their physical mechanisms.

Keywords: Neural networks, Radio pulsars, Pulsars