Sazuna/UAT_keywords huggingface dataset:
Origins of Mercury's Big Heart of Iron: Exploring Pathways to Form High Core Mass Fraction Planets via N-body Simulations. Mercury's core mass fraction (CMF) is 0.7, more than double that of the other rocky planets in the solar system, which have CMFs of 0.3 or lower. The origin of Mercury's large, iron-rich core remains unknown. Adding to this mystery, an elusive population of "exo-Mercuries" with high densities is emerging. Therefore, understanding the formation of Mercury and its exoplanetary analogs is essential to developing a comprehensive planet formation theory. Two hypotheses have been proposed to explain the high CMF of Mercury: (1) giant impacts during the latest stages of planet formation strip away mantle layers, leaving Mercury with a large core; and (2) earlier-stage iron enrichment of planetesimals closer to the Sun leads to the formation of an iron-rich planet. In this work, we conduct N-body simulations to test these two possibilities. Our simulations are focused on the solar system, however, we aim to provide a framework that can later be applied to the formation of high-CMF exoplanets. To investigate the giant impact scenario, we employ uniform initial CMF distributions. To address the other hypothesis, we use a step function with higher CMFs in the inner region. For a uniform initial CMF distribution, our results indicate that although erosive impacts produce iron-rich planetesimals, without mechanisms that deplete stripped mantle material, these planetesimals merge with lower-CMF objects and do not lead to Mercury's elevated CMF. However, a step-function initial CMF distribution leads to the formation of a high-CMF planet alongside Earth-like planets, resembling the architecture of the terrestrial solar system.

Keywords: Collision physics, N-body simulations, Planet formation, Mercury (planet)
Chemodynamics of Boötes I with S<SUP>5</SUP>: Revised Velocity Gradient, Dark Matter Density, and Galactic Chemical Evolution Constraints. We combine new spectroscopic observations of the ultrafaint dwarf (UFD) galaxy Boötes I (Boo I) from the Southern Stellar Stream Spectroscopic Survey (S5) with ∼15 yr of archival spectroscopic data to create the largest sample of stellar kinematics and metallicities to date for any Milky Way UFD. Our combined sample includes 148 members extending out to ∼7 half-light radii (rh), including 24 newly confirmed members, 18 binary candidates, 15 RR Lyrae stars, and 92 [Fe/H] measurements. Using this larger and more spatially extended sample, we provide updated constraints on Boo I's systemic properties, including its radial population gradients. Properly accounting for perspective rotation effects in a UFD for the first time, we detect a 4σ line-of-sight velocity gradient of 1.2 ± 0.3 km s−1  rh−1  aligned along Boo I's orbit and discuss its potential tidal origins. We also infer a metallicity gradient of −0.10 ± 0.02 dex  rh−1  in agreement with previous studies. Using an axisymmetric Jeans model, we provide updated constraints on Boo I's dark matter density profile, which weakly favors a cusped ( γ=1.0−0.6+0.5 ) dark matter profile. Lastly, we reanalyze Boo I's metallicity distribution function with a one-zone galactic chemical evolution model and place new constraints on its rapid, inefficient star formation and strong galactic outflows.

Keywords: Local Group, Galaxy chemical evolution, Stellar kinematics, Stellar abundances, Stellar populations, Dwarf galaxies, Dark matter
Tracking the Assembly of Supermassive Black Holes: A Comparison of Diverse Models across Cosmic Time. Galaxies grow alongside central supermassive black holes (SMBHs) through fueling and feedback. However, the origins of this coevolution remain unclear and vary across modeling frameworks. Using semianalytic models (SAMs), we trace SMBH mass assembly across MBH ∼ 106−10 M⊙. We find significant discrepancies between observations and physics-based models of the local black hole mass function (BHMF), likely from differences in the stellar mass function and scaling relations used to infer the BHMF. Most physics-based models agree at z ∼ 1─4 and broadly match the JWST broad-line active galactic nucleus (AGN) BHMFs at z = 4─5. These models also reproduce the observed bolometric AGN luminosity evolution, except the SAM DARK SAGE, which predicts an excess. Interestingly, this pronounced "knee" in the bolometric AGN luminosity function predicted by DARK SAGE around Lbol ∼ 1046 erg s−1 is consistent with the inferred abundance and luminosity of "little red dots" at z = 5─6, under the assumption that they are powered entirely by AGN activity. In contrast to other models, DARK SAGE deploys multiple growth channels for SMBHs that include mergers, hot-mode accretion, merger-driven cold-accretion, and secular-instability-driven accretion. We analyze the black hole mass buildup and accretion histories in DARK SAGE, which, unlike other models, also allows for super-Eddington accretion, and we find that, on average, SMBHs primarily grow through secular disk instabilities and merger-driven cold gas accretion modes. We also find that black hole mergers contribute the majority of the growth of ∼60% of the total mass budget only for the most massive SMBHs by z = 0.

Keywords: Galaxy formation, Astrophysical black holes
The Strongly Lensed Hα-emitting Galaxy Population at 3.8 &lt; z &lt; 6.6. Hα luminosity traces the ionizing-photon output of short-lived, massive stars and is therefore a key diagnostic of star formation in high-redshift galaxies. Recent JWST observations have delivered updated Hα luminosity functions (LFs) of Hα-emitting galaxies out to an unprecedented 3.8 &lt; z &lt; 6.6, yet strong gravitational lensing can systematically skew the bright end and bias the cosmic star formation rate (SFR) density inferred from the LF. To quantify the population of strongly lensed Hα-emitting galaxies at 3.8 &lt; z &lt; 6.6, we use Monte Carlo sampling based on these new LFs and gravitational-lensing ray-tracing simulations with lenstronomy: sources adopt Sérsic surface-brightness profiles; foreground deflectors are drawn from an empirical velocity-dispersion function to build a 900 deg2 light cone. In parallel, we convolve the intrinsic LF with the global magnification probability density to obtain an analytic approximation of lensed counts, which efficiently propagates intrinsic LF parameter uncertainties to lensed results. Our simulations show that ≳90% of Hα-emitting galaxies with SFR ≳ 103 M⊙ yr−1 are strongly lensed systems at 3.8 &lt; z &lt; 6.6, and the lensed number fraction per SFR bin rises from ∼10% to ∼90% across  log10SFR≃2.64 ─3.05 M⊙ yr−1. Given the  ∼62arcmin2  GOODS-South coverage and a 50%─100% overall completeness, the existing FRESCO and CONGRESS observations should contain ∼1.7─3.4 strongly lensed Hα-emitting galaxies with SFR &gt; 10 M⊙ yr−1. These results imply that, in the JWST era, analyses relying on samples with apparent SFR ≳ 103 M⊙ yr−1 must correct for strong lensing in order to obtain unbiased inferences.

Keywords: Luminosity function, Strong gravitational lensing, Emission line galaxies, Star formation, High-redshift galaxies
Betelgeuse: Detection of the Expanding Wake of the Companion Star. Recent analyses conclude that Betelgeuse, a red supergiant star (HD 39801), likely has a companion object with a period of ∼2000 days orbiting at only 2.3 R⋆, deep in the chromosphere of the supergiant. A probable detection of such a companion, named Siwarha, has just occurred from speckle imaging. This study finds that Betelgeuse spectra in the optical region and ultraviolet exhibit signatures of variable circumstellar absorption and chromospheric outflows. These variations are consistent with the ∼2000 days period of the companion object. Circumstellar absorption evident in optical Mn I lines, and mass outflow marked by ultraviolet Fe II, Si I, and Mg I lines increase after the transit of the companion across the disk of Betelgeuse. Following the eclipse of the companion, the absorption and outflow slowly decrease in advance of the next transit. The occurrence and variation of this plasma appear consistent with the presence of a trailing and expanding wake caused by a companion star orbiting within the atmosphere of Betelgeuse.

Keywords: Stellar chromospheres, M supergiant stars, Stellar atmospheres, Stellar mass loss
Tracking the Evolution of Plasma Instabilities from the Prominence─Corona Transition Region into Interplanetary Space with Total Solar Eclipse and PSP/WISPR White Light Images. High-resolution total solar eclipse (TSE) white light (WL) images are the only observations at present to capture coronal structures over an uninterrupted field of view (FoV) of at least 10 solar radii (Rs) starting from the solar limb. They were the first to report the presence of vortex rings originating within the prominence─corona transition region (PCTR). They have also captured coronal mass ejections (CMEs) and Kelvin─Helmholtz (KH) instabilities at different phases of their evolution. While the evolution of CMEs and KH waves is relatively well documented, little is known about the survivability of vortex rings beyond the FoV of TSE images. In this study, we use seven TSE images and noncontemporaneous WL images acquired by the Wide-field Imager for Parker Solar Probe (WISPR) to track the spatial evolution of vortex rings, KH waves, and CMEs. The size trend versus radial distance for vortex rings and KH waves is found to be shallower below 1.5 Rs than beyond 3 Rs, while the CMEs observed beyond 3 Rs show a unique slope. The WISPR time series yields an average speed of 249.02 ± 25.3 km s−1 for the vortex rings beyond 3 Rs, which when combined with their size yields a speed of 19.39 ± 3.20 km s−1 below 1 Rs. These values are remarkably consistent with the acceleration profile of the slow solar wind over the same distance. This study provides strong empirical evidence that vortex rings, which originate at the PCTR with complex magnetic structures, do not dissipate as they expand away from the Sun with the solar wind.

Keywords: Solar prominences, Heliosphere, The Sun, Solar corona, Solar magnetic fields
Diffusion-free Dynamics in Rotating Spherical Shell Convection Driven by Internal Heating and Cooling. The bulk properties of convection in stellar and giant planet interiors are often assumed to be independent of the molecular diffusivities, which are very small. By contrast, simulations of this process in rotating spherical shells, which are typically driven by conductive boundary heat fluxes, generally yield results that depend on the diffusivity. This makes it challenging to extrapolate these simulation results to real objects. However, laboratory models and Cartesian-box simulations suggest that diffusion-free dynamics are more readily obtained if convection is driven using prescribed internal heating and cooling instead of boundary fluxes. Here, we apply this methodology to simulations of Boussinesq, hydrodynamic rotating spherical shell convection. We find that this setup unambiguously yields diffusion-free behavior for some bulk properties of the convection, such as the radial temperature contrast and the convective heat transport. Moreover, the transition from prograde to retrograde equatorial zonal flow is diffusion free and only depends on the convective Rossby number. The diffusivity dependence of other bulk properties is regime dependent. In simulations that are rotationally constrained, the convective velocities and the strength and structure of the zonal flow are diffusion dependent, although the zonal flow appears to approach a diffusion-free state for sufficiently high supercriticality. In simulations that are either uninfluenced by rotation or influenced by rotation only at large scales, diffusion-free convective velocities and zonal flows are obtained. The result that many aspects of our idealized simulations are diffusion free has promising implications for the development of realistic stellar and giant planet convection models that can access diffusion-free regimes.

Keywords: Stellar convective zones, Planetary atmospheres, Solar physics
ALMA Band 7 Observations of Water Lines in the Protoplanetary Disk of V883 Ori. The FU Orionis star V883 Ori provides a unique opportunity to probe the water snowline in a protoplanetary disk. During an accretion burst, the enhanced stellar luminosity heats the disk, sublimating ices and bringing volatile species into the gas phase. The water snowline, located at ∼80 au in the midplane, represents a key boundary for dust growth and volatile delivery to forming planets. We present Atacama Large Millimeter/submillimeter Array Band 7 observations of V883 Ori that detect two targeted water isotopologue transitions: para-H2 18O 51,5─42,2 at 322 GHz and HDO 33,1─42,2 at 335 GHz. After correcting for Keplerian rotation, we detect HDO and H2 18O at 23.6σ and 9.3σ, respectively. Rotational-diagram analysis using a Markov Chain Monte Carlo approach yields Trot = 116.89 ± 12.81 K and N = (4.90 ± 1.69) × 1015 cm−2 for H2 18O and Trot = 87.46 ± 4.95 K and N = (4.47 ± 0.62) × 1015 cm−2 for HDO. These results imply water vapor abundances of  NH2O/NH2∼3×10−7 ─5 × 10−6 and an HDO/H2O ratio of (0.4─2.0) × 10−3 just inside the water snowline, broadly consistent with inheritance from protostellar envelopes. The HDO line in Band 7 is significantly weaker than predicted from Band 6 extrapolation, showing only ∼26% of the expected strength. This attenuation can be explained by a more compact, hotter emitting region with an effective radius of ∼53 au and/or frequency-dependent dust absorption that enlarges the apparent inner cavity at a higher frequency. Our results highlight both the diagnostic power of water isotopologue lines and the need for higher angular resolution observations to resolve the water snowline and test these scenarios.

Keywords: Protoplanetary disks, Astrochemistry
Spectroscopic Follow-up of Gaia Alerted Young Stellar Object Variables: The Large Binocular Telescope View. We analyzed optical/near-IR Large Binocular Telescope spectra of 16 sources alerted by Gaia between 2021 and 2024 due to significant photometric variability. Half of the spectra were taken during quiescence and the rest during a burst or at intermediate brightness. Our analysis of their 10 yr light curves and photometric/spectroscopic features provides evidence that all 16 sources are accreting young stellar objects (YSOs). One object, Gaia23bab, is a known EXor source. Other light curves either have peaks over a stable baseline or significant variability throughout the entire observation period, suggesting multiple contributing processes. All spectra exhibit emission lines from accretion columns, and over half of them show atomic forbidden lines as signatures of outflowing gas. We determined stellar parameters, accretion luminosity (Lacc), and mass accretion rate ( Ṁacc ) at different brightness phases. Only two sources showed variability primarily due to extinction. During quiescence, our sources exhibit Lacc and  Ṁacc  values typical of T Tauri and Herbig Ae/Be (HAeBe) sources, supporting the hypothesis that any YSO may undergo episodic accretion. In bursts, the Lacc and  Ṁacc  of sources with photometric variations exceeding 2 mag follow a shallower relation with stellar luminosity and mass, typical of known EXor sources. This group includes one Class I, one flat-spectrum, and two Class II sources. Notably, the other Class I source, Gaia24beh, shows an Lacc value about 10 times higher than typical EXor bursts of the same mass. In the other cases, Lacc and  Ṁacc  align with variability seen in T Tauri and HAeBe sources.

Keywords: Pre-main sequence stars, Star formation, Eruptive variable stars, Stellar accretion
Asteroseismology for Probing the Interior Structure and Orbital Stability of Extremely Low Mass Ratio Contact Binaries. Theoretical investigations predict a minimum mass ratio of about 0.085─0.095 for contact binaries. If the mass ratio is below the critical value, a tidal instability occurs, forcing the stars to merge into a single object. Observationally, however, more and more W UMa-type binaries have been found to have mass ratios lower than the theoretical limit. In this study, we try to solve this discrepancy by considering the stellar structure and evolution probed through asteroseismology. We searched for and detected gravity (g)- and Rossby (r)-mode pulsations in four contact binaries with mass ratios less than 0.1. A seismic study of the pulsations led us to identify the pulsation modes and determine the near-core and envelope rotation rates as well as the asymptotic period spacings of the pulsating, primary stars. By asteroseismic modeling, the stellar parameters were constrained, and the structure models were constructed. This enables us to determine the gyration radii of the primaries and investigate in detail the orbital stability of the contact systems. We indicate that both the mass and age have independent effects on orbital stability, with massive and older primaries being more stable. Moreover, differential core-to-surface rotation would significantly reduce the gyration radius and hence the minimum mass ratio of a contact system. Adopting the median value of the gyration radius derived for the four stars, we estimate a critical mass ratio of 0.042─0.044, depending on the filling factor.

Keywords: Asteroseismology, Contact binary stars
FEASTS Compared with Simulations: Abnormally Irregular and Extended H I Morphologies at a Column Density of 10<SUP>18</SUP> cm<SUP>−2</SUP> in TNG50 and Auriga. With new atomic-hydrogen (H I) observations of FAST Extended Atlas of Selected Targets Survey (FEASTS), we present the first statistical comparison of H I morphology between observations and cosmological simulations, focusing on low-column-density (∼1018 cm−2) regions of Milky Way─like central galaxies. We select a 330-galaxy sample from IllustrisTNG50 (TNG50) matched to 33 FEASTS galaxies by stellar and H I masses, and mock observe them at the FAST resolution and depth at corresponding inclinations and distances for a fair comparison. In contrast to FEASTS, abnormally irregular and extended morphology is found in more than one-third of TNG50 galaxies, especially those that are massive and H I poor. Stellar feedback is the property that most significantly correlates with the H I morphological deviation from observations, although these deviations mostly occur at a high stellar or black-hole mass. These results indicate that, in TNG50, stellar feedback significantly influences the H I morphology at ∼1018 cm−2, while active galactic nucleus (AGN) feedback has not so direct a role as expected. With an additional sample from Auriga, we find that the magnetic field may help H I to be more regular in its morphology, while improving the mass resolution does not alleviate the discrepancy from observation. This study reveals the potential of constraining future simulations of galaxies by observing low-column-density H I.

Keywords: Galaxy accretion, Interstellar atomic gas, Circumgalactic medium
Ignition of Weak Interactions and r-process Outflows in Supercollapsar Accretion Disks. The collapse of rotating massive (∼10M⊙) stars resulting in hyperaccreting black holes (BHs; "collapsars") is a leading model for the central engines of long-duration gamma-ray bursts (GRBs) and a promising source of rapid neutron-capture (r-process) elements. R-process nucleosynthesis in disk outflows requires the accretion flow to neutronize. This occurs because of Pauli blocking at finite electron degeneracy, associated with a critical accretion rate  Ṁ&gt;Ṁign . We analytically examine the assumptions underlying this "ignition threshold" and its possible breakdown with increasing BH mass M∙. Employing three-dimensional general-relativistic magnetohydrodynamic simulations with weak interactions, we explore the physical conditions of collapsar accretion disks with M∙ ∼ 80−3000M⊙ over more than a viscous timescale as they transition through the threshold. There is remarkable agreement between our simulations and the analytic result  Ṁign∝α5/3M∙4/3  for M∙ ∼ 3−3000M⊙. Simulations and analytic analyses consistently show that the largest BHs leading to r-process nucleosynthesis at  ≳Ṁign  are ≍3000M⊙, beyond which neutronization ceases, since the disk temperature  T∝M∙−1/6  decreases below the neutron─proton mass difference (≃MeV), suppressing the conversion of protons into neutrons. We show that stellar models of ∼250−105M⊙ can give rise to BHs of M∙ ∼ 30−1000M⊙ accreting at  Ṁ≳Ṁign , yielding potentially up to ∼10−100M⊙ of light and heavy r-process elements per event. These rare but prolific r-process sources in low-metallicity environments are associated with super-kilonovae and likely extremely energetic GRBs. Such signatures may be used to probe Population III stars.

Keywords: Black holes, High energy astrophysics, Nucleosynthesis, Gamma-ray sources, R-process, Massive stars, Nuclear astrophysics, General relativity, Gravitational collapse, Compact objects, Stellar accretion disks, Magnetohydrodynamical simulations
A Mysterious Feature in the NICER Spectrum of 4U 1820-30: A Gravitationally Redshifted Absorption Line?. A mysterious absorption feature at approximately 3.8 keV has been identified in the Neutron star Interior Composition Explorer (NICER) spectrum of the low-mass X-ray binary system 4U 1820-30. We interpret this feature as a gravitationally redshifted iron absorption line. This interpretation is supported by the temporal proximity of the NICER observation to the detection of a carbon superburst—a long and intense thermonuclear flash on the neutron star's surface—by the X-ray monitor MAXI, suggesting that the presence of the line is associated with this rare and extreme event. From the inferred redshift of the absorption line, the compactness of the neutron star can be derived. Fitting this feature with a photoionization absorption model, we measure a redshift of 1 + z ≃ 1.72, which implies a neutron star compactness of R/M = 4.46 ± 0.13 km/M⊙ or 3.02 ± 0.09 in dimensionless units. This unique feature highlights the importance of further observations and detailed modelling, offering promising insights into the equation of state of matter under extreme density conditions.

Keywords: Neutron stars, General relativity, Spectroscopy, Low-mass x-ray binary stars, X-ray bursts
Death by Impact: Evidence for Merger-driven Quenching in a Collisional Ring Galaxy at Cosmic Noon. The role of interactions and mergers in the rapid quenching of massive galaxies in the early Universe remains uncertain, largely due to the difficulty of directly linking mergers to quenching. Collisional ring galaxies provide a unique opportunity, as their morphology allows precise dating of the interaction, which can then be compared to quenching timescales inferred from star formation histories. We study a gravitationally bound system at z = 1.61 in the Ultra Deep Survey field, composed of a host galaxy (M⋆ = 1011.4 M⊙) with a collisional ring and an X-ray active galactic nucleus (AGN), and the Bullet Galaxy (M⋆ = 1011.2 M⊙), located at a projected distance of ∼8 kpc. Combining JWST and Hubble Space Telescope imaging with Keck/MOSFIRE spectroscopy, we find compelling evidence for an ongoing starburst in the host concurrent with rapid quenching in the Bullet Galaxy. The ring, ∼20 kpc in diameter, is expanding at  127−29+72  km s−1, implying the galaxies first collided 47─96 Myr ago. This timeline is consistent with the host's current starburst and the Bullet Galaxy's sudden quenching, strongly suggesting both phenomena were triggered by the interaction. Crucially, the Bullet Galaxy shows no evidence of a preceding starburst, ruling out rapid gas consumption as the primary quenching channel. Instead, we suggest that merger-driven processes—such as enhanced turbulence and disk instabilities—may have suppressed star formation. An additional possibility, which we term the dragon effect, is that AGN-driven outflows from the host disrupted the Bullet Galaxy's low-density molecular gas, thereby preventing efficient star formation and accelerating quenching.

Keywords: AGN host galaxies, Galaxy interactions, Ring galaxies, Galaxy mergers, Galaxy evolution, Galaxy quenching, High-redshift galaxies, Galaxy processes