Sazuna/UAT_keywords huggingface dataset:
Spectroscopic Reverberation Mapping for SARM: The Case of Mrk 1048 and Mrk 618. Robust extragalactic distance measurements are crucial for resolving the persistent discrepancy in the value of the Hubble constant (H0). Active galactic nuclei (AGNs), through their compact and variable broad-line regions, enable the determination of geometric distances when reverberation mapping (RM) is combined with spectroastrometry. We report results from a spectroscopic RM campaign (2022 October─2023 March) targeting two narrow-line Seyfert 1 galaxies, Mrk 1048 and Mrk 618, using the 3.6 m Devasthal Optical Telescope and 2 m Himalayan Chandra Telescope. High-cadence spectrophotometric monitoring was carried out using onboard instruments such as ADFOSC, HFOSC, and TANSPEC, resulting in well-sampled continuum and emission-line light curves. The observed fractional variability (Fvar) ranged from 4% to 14% across the g-band, Hβ, and Hα light curves. The time lags were measured using the interpolated cross-correlation function (ICCF), PyI2CCF, and JAVELIN methods. In the rest frame, the ICCF analysis yields Hβ lags of  10.5−4.2+2.6  days for Mrk 1048 and  10.2−2.9+3.4  days for Mrk 618, while the corresponding Hα lags are  18.7−5.4+5.3  and  14.4−10.5+4.6  days, respectively. The emission-line widths, measured from the rms spectra using σline, give virial black hole mass estimates of  6.3−2.1+2.0×107M⊙  for Mrk 1048 and  1.2−0.6+0.4×107M⊙  for Mrk 618. These results will serve as a basis for absolute geometric distance calibration when combined with VLTI/GRAVITY spectroastrometric measurements, thereby contributing to the development of AGNs as standardizable cosmological probes.

Keywords: Black holes, Reverberation mapping, Distance measure, Active galactic nuclei, Optical telescopes
Asteroseismic Calibration of the Rossby Number and Its Connection to the Stellar Dynamo and Fundamental Properties. The stellar Rossby number, a dimensionless parameter quantifying the influence of Coriolis forces on convective motions, plays a pivotal role in understanding magnetic stellar evolution. In this work, we explore the connection between the Rossby number and potential dynamo mechanisms in Sun-like stars, as well as its dependence on fundamental stellar properties. We present a novel, detailed asteroseismic calibration of the convective turnover time, incorporating for the first time Gaia photometry alongside surface gravity, effective temperature, and stellar metallicity. Our analysis employs an expanded sample of more than 150 stars, including targets from the Kepler LEGACY and Kepler Objects of Interest surveys, as well as more evolved stars observed by TESS and K2. This sample spans evolutionary stages from the main sequence to the early red giant branch, enabling a comprehensive investigation of Rossby number trends across stellar evolution.

Keywords: Low mass stars, Stellar properties, Stellar activity
Insights into Planet Formation from the Ages, Masses, and Elemental Abundances of Host Stars. How planetary systems form and evolve is a key question in astronomy. Revealing how host star properties—such as elemental abundances, age, and mass—differ from those of nonhost stars, and how they correlate with planetary characteristics such as radius, provides new insights into the formation and evolutionary pathways of planetary systems. We determine precise ages for 18,890 dwarfs and subgiants from the LAMOST─Kepler─Gaia sample with a mean age uncertainty ∼15% (median ∼10%). Within the framework of Galactic chemical evolution, we find that ∼86% of planet-hosting stars younger than 8 Gyr occupy the upper branch ([Fe/H] &gt; −0.2) of the characteristic "V-shape" age─metallicity relation of the Galactic disk. Based on guiding radii (Rg), we further infer that ∼19% of these young hosts likely originated in the inner disk and subsequently migrated to the solar neighborhood. Among stars older than 10 Gyr, host stars tend to be more metal-rich, with nearly 59% having [Fe/H] &gt; −0.2. This suggests that both young and old planet-hosting stars preferentially form in relatively metal-rich environments. However, for host stars with [Fe/H] &lt; −0.2, we find that their [Fe/H] is on average lower by ∼0.16 dex compared to nonhost stars of similar age and mass, indicating that [Fe/H] is unlikely to be the dominant factor governing planet formation in metal-poor environments. We also identify systematic depletion of volatile elements—especially carbon—in planet hosts. Moreover, host star [Fe/H] exhibits a weak correlation with planet radius, while [α/Fe] primarily supports the formation of small planets.

Keywords: Galaxy chemical evolution, Stellar ages, Exoplanets, Stellar masses
Gamma Rays as a Signature of r-process Producing Supernovae: Remnants and Future Galactic Explosions. We consider the question of whether core-collapse supernovae (CCSNe) can produce rapid neutron capture process (r-process) elements and how future MeV gamma-ray observations could address this. Rare types of CCSNe characterized by substantial magnetic fields and rotation, known as magnetorotational supernovae (MR-SNe), are theoretically predicted to produce these elements, although direct observational evidence is lacking. We suggest that this critical question be addressed through the study of some of the 11 CCSN remnants located within 10 kpc, as well as through the detection of gamma-ray emission from a future Galactic supernova. We use a two-dimensional MR-SN model to estimate the expected gamma flux stemming from nuclear decays in the range of a few tens of keV to a few MeV. Our results indicate that an observation of 126Sn (126Sb) in a remnant stands out as a signature of an r-process-producing supernova. Since the neutron-rich conditions that lead to the production of the r-process could also enhance the production of 60Fe, the detection of substantial 60Fe (60Co) would be indicative of favorable conditions for the r-process. In the case of a future supernova explosion, when the evolution of the spectrum is studied over 10 days to a few years, a rich picture emerges. At various epochs, the second peak r-process isotopes such as 125Sn, 131I, 132Te, 132I, and 140La produce signals that are not obscured by the gamma emission from explosive burning products and electron─positron annihilation. The weak r-process isotopes 95Nb, 103Ru, and 106Rh also have periods of prominence.

Keywords: Nucleosynthesis, R-process, Supernova remnants, Supernovae, Gamma-rays
Gaussian Process Methods for Very Large Astrometric Data Sets. We present a novel nonparametric method for inferring smooth models of the mean velocity field and velocity dispersion tensor of the Milky Way from astrometric data. Our approach is based on stochastic variational Gaussian process regression (SVGPR) and provides an attractive alternative to binning procedures. SVGPR is an approximation to standard Gaussian process regression (GPR), the latter of which suffers severe computational scaling with N and assumes independently distributed Gaussian noise. In the Galaxy, however, velocity measurements exhibit scatter from both observational uncertainty and the intrinsic velocity dispersion of the distribution function. We exploit the factorization property of the objective function in SVGPR to simultaneously model both the mean velocity field and velocity dispersion tensor as separate Gaussian processes. This achieves a computational complexity of O(M3) versus GPR's O(N3), where M &lt; &lt; N is a subset of points chosen in a principled way to summarize the data. Applied to a sample of ∼8 × 105 stars from the Gaia DR3 Radial Velocity Survey catalog, we construct differentiable profiles of the mean velocity and velocity dispersion as functions of height above the Galactic midplane. We find asymmetric features in all three diagonal components of the velocity dispersion tensor, providing evidence that the vertical dynamics of the Milky Way are in a state of disequilibrium. Furthermore, our dispersion profiles exhibit correlated structures at several locations in ∣z∣, which we interpret as signatures of the Gaia phase spiral. Our method also has interdisciplinary applicability for any data set requiring simultaneous modeling of both latent functions and input-dependent noise.

Keywords: Stellar kinematics, Milky Way dynamics, Galaxy kinematics, Gaussian Processes regression, Milky Way Galaxy
Unveiling Central Ortho-H<SUB>2</SUB>D<SUP>+</SUP> Depletion at Sub-kau Scales in Prestellar Core G205.46-14.56 M3: The First Interferometric Evidence and Implications for Deuterium Chemistry. Prestellar cores represent the initial conditions of star formation, but heavy molecules such as CO are strongly depleted in their cold, dense interiors, limiting the ability to probe core centers. Deuterated molecular ions therefore emerge as key tracers because deuterium fractionation is enhanced at low temperatures. We present the first direct observation of ortho-H2D+ depletion in the prestellar core G205.46−14.56 M3 using ALMA 820 μm continuum and ortho-H2D+ (110─111) data at ∼300 au resolution. We confirm the previously reported two substructures, B1 and B2, and identify a central ortho-H2D+ depletion zone toward B1 with ∼6σ contrast and an inferred diameter ≲600 au, together with a peak x(N2D+)/x(N2H+) =  1.03−0.56+0.07 . The observationally inferred profiles of x(ortho-H2D+) and x(N2D+)/x(N2H+) are reproduced by a deuteration-focused chemodynamical model; however, the central o-H2D+ depletion is only marginally matched within the 2σ upper limit, likely suggesting additional deuteration in the depletion zone. From these models we infer a core age of ∼0.42 Ma, comparable to the freefall time, suggesting that the substructures formed via rapid, turbulence-dominated fragmentation rather than slow, quasistatic contraction. Our observations also reveal that ortho-H2D+ velocity dispersions are largely subsonic in the core and nearly thermal between B1 and B2, consistent with turbulence dissipating within a few freefall times. These results highlight the critical role of deuterated ions for both chemical evolution and dynamics in dense cores.

Keywords: Star forming regions, Molecular clouds, Astrochemistry, Star formation, Interstellar medium, Submillimeter astronomy
Probing the Physical Origin of the Balmer Decrement in the Broad-line Region of Nearby Active Galactic Nuclei via Spectral Variability. To investigate the physical origin of the Balmer decrement in the broad-line region of active galactic nuclei (AGNs), we measure the temporal variability of the fluxes of the broad Hβ and Hα emission lines using multiepoch spectroscopic data of low-redshift AGNs from the Sloan Digital Sky Survey. The analysis of the mean spectra reveals that the Balmer decrement shows no correlation with AGN luminosity, while it is inversely correlated with the Eddington ratio. However, the temporal variation of the Balmer decrement in individual objects exhibits an even stronger anticorrelation with AGN luminosity, suggesting that the change in AGN luminosity plays a dominant role in determining the Balmer decrement. By comparing the temporal evolution of the Balmer decrement with the continuum color, we find that reddening due to the AGN itself may not be the primary factor. Instead, radiative transfer effects and excitation mechanisms, which deviate from the Case B recombination, appear to be critical for the variation of the Balmer decrement. These results provide useful insights into the underlying physics of changing-look AGNs and high-z AGNs, such as the "little red dots," which exhibit extreme values of the Balmer decrement that can be misinterpreted as evidence for dust.

Keywords: Active galaxies
Hadronic Processes in Advection-dominated Accretion Flow as the Origin of TeV Excesses in BL Lac Objects. The spectral energy distributions (SEDs) of certain BL Lac objects (BL Lacs) exhibit an additional hard γ-ray component in the TeV energy range that surpasses the predictions of the one-zone leptonic jet model. The origin of this excess emission remains unclear. In this study, we selected five BL Lacs whose SEDs display a very hard intrinsic spectrum in the TeV band and successfully reproduced their broadband SEDs using a two-zone leptohadronic model. Within this framework, the emission observed in the optical, X-ray, GeV γ-ray, and sub-TeV γ-ray bands is modeled using the synchrotron and synchrotron self-Compton radiation processes of the relativistic electrons in the jets. Meanwhile, the TeV excess is attributed to γ-ray emission resulting from the photomeson (pγ) process via π0 decay occurring within advection-dominated accretion flows (ADAFs). This scenario requires a hard proton spectrum with a spectral index of p ∼ 1.6─1.7 and a cutoff energy ranging from 30 to 90 TeV, as well as a relatively large ADAF radius. Such hard proton spectra suggest that the dominant acceleration mechanisms are likely magnetic reconnection and/or stochastic acceleration processes within ADAFs. Additionally, the emission from the cascaded electrons results in a bump in the keV─MeV band; however, it is overwhelmed by the jet emission. Although the hadronuclear (pp) process cannot be entirely ruled out, it would necessitate an even harder proton spectrum and a higher cutoff energy compared to the pγ process, making it a less favorable explanation for the observed TeV excess.

Keywords: BL Lacertae objects, Relativistic jets, Galaxy accretion disks, Active galactic nuclei, Gamma-rays
On the Gravitational Collapse of Small Dust Grains in Self-gravitating Disk Structures. Planet formation may begin much earlier than previously expected, when the protoplanetary disk is still massive and gravitationally unstable. It has been proposed that solid grains can concentrate in the spiral arms of self-gravitating disks, leading to the formation of planetary embryos or cores that can greatly accelerate the process of planet formation. We perform hydrodynamic simulations of self-gravitating gas and even smaller dust grains than previously investigated in three-dimensional shearing box simulations to explore the conditions necessary to form these planetary seeds. Focusing on small grains of dimensionless stopping time St = 0.01 and shorter, we find that disk metallicities Z ≳ 0.02 can overcome the disruptive effects of dust diffusion among these small dust grains. In the outer reaches of a gravitationally unstable disk, these models correspond to grains of approximately 1 mm and lead to planetary embryos between 0.1 and 1 Earth mass. The formation of these planetary embryos could therefore reduce the time needed for planet assembly, particularly in the outer regions of the disk where coagulation timescales are longer and solid growth is limited.

Keywords: Hydrodynamical simulations, Protoplanetary disks, Planet formation, Planetesimals
Two-stage Nature of a Solar Flare with Parallel and Semicircular Ribbons. Flare ribbons with parallel and circular morphologies are typically associated with different magnetic reconnection models, and the simultaneous observation of both types in a single event remains rare. Using multiwavelength observations from a tandem of instruments, we present an M8.2-class flare that occurred on 2023 September 20, which produced quasi-parallel and semicircular ribbons. The complex evolution of the flare includes two distinct brightening episodes in the quasi-parallel ribbons, corresponding to the two major peaks in the hard X-ray (HXR) light curve. In contrast, the brightening of semicircular ribbons temporally coincides with the local minimum between the two peaks. Using potential field extrapolation, we reconstruct an incomplete dome-like magnetic structure with a negative polarity embedded within the northwestern part of the semicircular positive polarity. Consequently, the magnetic configuration comprises two sets of field lines with distinct magnetic connectivities. We suggest that the standard flare reconnection accounts for the two-stage brightening of quasi-parallel ribbons associated with the two HXR peaks. Between the two stages, this process is constrained by the interaction of eruptive structures with the dome. The interaction drives the quasi-separatrix layer reconnection, leading to the brightening of semicircular ribbons. It also suppresses the standard flare reconnection, resulting in a delayed second HXR peak.

Keywords: Solar flares, Solar magnetic reconnection, Solar x-ray emission, Solar magnetic fields, Solar activity
3D Modeling of Moist Convective Inhibition in Idealized Sub-Neptune Atmospheres. Atmospheric convection behaves differently in hydrogen-rich atmospheres compared to higher mean molecular weight atmospheres due to compositional gradients of tracers. Previous 1D studies predict that when a condensable tracer exceeds a critical mixing ratio in H2-rich atmospheres, convection is inhibited, leading to the formation of radiative layers where the temperature decreases faster with height than in convective profiles. We use 3D convection-resolving simulations to test whether convection is inhibited in H2-rich atmospheres when the tracer mixing ratio exceeds the critical threshold, while including processes neglected in 1D, e.g., turbulent mixing and evaporation. We run two sets of simulations. First, we perform simulations initialized on saturated isothermal states and find that compositional gradients can destabilize isothermal atmospheres. Second, we perform simulations initialized on adiabatic profiles, which show distinct, stable inhibition layers form when the condensable tracer exceeds the critical threshold. Within the inhibition layer, only a small amount of energy is carried by latent heat flux, and turbulent mixing transports a small amount of tracer upward, but both are generally too weak to sustain substantial tracer or heat transport. The thermal profile gradually relaxes to a steep radiative state, but radiative relaxation timescales are long. Our results suggest stable layers driven by condensation-induced convective inhibition form in H2-rich atmospheres, including those of sub-Neptune exoplanets.

Keywords: Exoplanet atmospheric composition , Planetary atmospheres, Exoplanet atmospheres, Atmospheric structure
An AI Superresolution Field Emulator for Cosmological Hydrodynamics: The Lyα Forest. We extend our superresolution and emulation framework for cosmological dark matter simulations to include hydrodynamics. We present a two-stage deep learning model to emulate high-resolution baryonic fields from low-resolution (LR-HydroSim) simulations at redshift z = 3. The method takes as inputs an LR-HydroSim and the high-resolution initial conditions (HR-HydroICs). First, the model stochastically generates high-resolution baryonic fields from the LR-HydroSim. Second, a deterministic emulator refines these fields using HR-HydroICs to reconstruct small-scale structures, including displacement, velocity, internal energy, and gas/star classification. Trained on paired low- and high-resolution simulations produced with MP-Gadget, the model captures small-scale structures of the intergalactic medium and observables down to the 100 kpc pressure smoothing scale relevant to the Lyα forest. The model achieves subpercent error for overdensity, temperature, velocity, and optical depth fields, a mean relative error of 1.07% in the large-scale flux power spectrum (k &lt; 3 × 10−2 s km−1), and less than 10% error in the flux probability distribution function. Notably, the two-stage model reduces the computational time by a factor of ∼260 compared to full smoothed particle hydrodynamics at the same resolution. This work demonstrates the potential of this framework as a powerful and efficient tool for generating high-resolution fields offering fast and accurate alternatives to traditional cosmological hydrodynamic simulations and enabling large-volume mock datasets for next-generation cosmological surveys.

Keywords: Hydrodynamical simulations, Lyman alpha forest, Large-scale structure of the universe
EPOCHS. III. Unbiased UV Continuum Slopes at 6.5 &lt; z &lt; 13 from Combined PEARLS GTO and Public JWST/NIRCam Imaging. We present an analysis of rest-frame UV continuum slopes, β, using a sample of 1011 galaxies at 6.5 &lt; z &lt; 13 from the EPOCHS photometric sample collated from the GTO PEARLS and public ERS/GTO/GO (JADES, CEERS, NGDEEP, GLASS) JWST/NIRCam imaging across  178.9arcmin2  of unmasked blank sky. We correct our UV slopes for the photometric error coupling bias using 200,000 power-law spectral energy distributions for each β = {−1, −1.5, −2, −2.5, −3} in each field, finding biases as large as ∆β ≃ −0.55 for the lowest signal-to-noise ratio galaxies in our sample. Additionally, we simulate the impact of rest-UV line emission (including Lyα) and damped Lyα systems on our measured β, finding biases as large as 0.5─0.6 for the most extreme systems. We find a decreasing trend with redshift of β = −1.51 ± 0.08 − (0.097 ± 0.010) × z, with potential evidence for Population III stars or top-heavy initial mass functions in a subsample of 68 β + σβ &lt; −2.8 galaxies. At z ≃ 11.5, we measure an extremely blue β(MUV = −19) = −2.73 ± 0.06, deviating from simulations, indicative of low-metallicity galaxies with nonzero Lyman continuum escape fractions fesc,LyC ≳ 0 and minimal dust content. The observed steepening of  dβ/dlog10(M⋆/M⊙)  from 0.22 ± 0.02 at z ≃ 7 to 0.81 ± 0.13 at z ≃ 11.5 implies that dust produced in core-collapse supernovae at early times may be ejected via outflows from low-mass galaxies. We also observe a flatter dβ/dMUV = 0.03 ± 0.02 at z ≃ 7 and a shallower  dβ/dlog10(M⋆/M⊙)  at z &lt; 11 than seen by the Hubble Space Telescope, unveiling a new population of low-mass, faint galaxies reddened by dust produced in the stellar winds of asymptotic giant branch stars or carbon-rich Wolf─Rayet binaries.

Keywords: Ultraviolet astronomy, High-redshift galaxies, Infrared telescopes, Dust formation
On the Fate of Little Red Dots. We study the stability and possible fates of little red dots (LRDs) under the stellar-only interpretation of their observational features. This is performed by a combination of analyzing the relevant timescales in their stellar dynamics and also the application of recent numerical results on the evolution of the densest stellar systems. We find that these objects typically have tage ∼ tcoll &lt; trelax and are therefore in an unexplored regime never observed before for a stellar system and are potentially highly unstable to runaway collisions. We study different scenarios for the evolution of LRDs and conclude that in a fair fraction of those systems, the formation of a massive black hole (MBH) by runaway stellar collisions seems unavoidable, in all the possibilities studied within the stellar-only interpretation. This evolutionary path would naturally explain many of the problematic characteristics of Little Red Dots, including that these objects are probably transient in the history of the Universe, that most of them would not emit X-rays since they would not yet have become MBHs, and once they do, they would constitute a significant portion of the mass of LRDs. We conclude that LRDs are the most favorable known places to find a recently formed MBH seed or, in the process of formation, that are most probably formed directly within the supermassive range.

Keywords: Astrophysical black holes