Sazuna/UAT_keywords huggingface dataset:
Model Choice Matters for Age Inference on the Red Giant Branch. Galactic archaeology relies on accurate stellar parameters to reconstruct the Galaxy's history, including information on stellar ages. While the precision of data has improved significantly in recent years, stellar models used for age inference have not improved at a similar rate. In fact, different models yield notably different age predictions for the same observational data. In this paper, we assess the difference in age predictions of various widely used model grids for stars along the red giant branch. Using open-source software, we conduct a comparison of four different evolution grids, and we find that age estimations become less reliable if stellar mass is not known, with differences occasionally exceeding 80%. Additionally, we note significant disagreements in the models' age estimations at nonsolar metallicity. Finally, we present a method for including theoretical uncertainties from stellar evolutionary tracks in age inferences of red giants, aimed at improving the accuracy of age estimation techniques used in the galactic archaeology community.

Keywords: Stellar properties, Stellar ages, Stellar evolutionary models, Red giant branch
A Two-week IXPE Monitoring Campaign on Mrk 421. X-ray polarization is a unique new probe of the particle acceleration in astrophysical jets made possible through the Imaging X-ray Polarimetry Explorer. Here we report on the first dense X-ray polarization monitoring campaign on the blazar Mrk 421. Our observations were accompanied by an even denser radio and optical polarization campaign. We find significant short-timescale variability in both X-ray polarization degree and angle, including an ∼90° angle rotation about the jet axis. We attribute this to random variations of the magnetic field, consistent with the presence of turbulence but also unlikely to be explained by turbulence alone. At the same time, the degree of lower-energy polarization is significantly lower and shows no more than mild variability. Our campaign provides further evidence for a scenario in which energy-stratified shock-acceleration of relativistic electrons, combined with a turbulent magnetic field, is responsible for optical to X-ray synchrotron emission in blazar jets.

Keywords: X-ray astronomy, Jets, Radio jets, Markarian galaxies, Blazars, Time domain astronomy, Shocks, Polarimetry
Union through UNITY: Cosmology with 2000 SNe Using a Unified Bayesian Framework. Type Ia supernovae (SNe Ia) were instrumental in establishing the acceleration of the Universe's expansion. By virtue of their combination of distance reach, precision, and prevalence, they continue to provide key cosmological constraints, complementing other cosmological probes. Individual SN surveys cover only over about a factor of 2 in redshift, so compilations of multiple SN data sets are strongly beneficial. We assemble an up-to-date "Union" compilation of 2087 cosmologically useful SNe Ia from 24 data sets ("Union3"). We take care to put all SNe on the same distance scale and update the light-curve fitting with SALT3 to use the full rest-frame optical. Over the next few years, the number of cosmologically useful SNe Ia will increase by more than a factor of 10, and keeping systematic uncertainties subdominant will be more challenging than ever. We discuss the importance of treating outliers, selection effects, light-curve shape/color populations/standardization relations, unexplained dispersion, and heterogeneous observations simultaneously. We present an updated Bayesian framework, called UNITY1.5 (Unified Nonlinear Inference for Type-Ia cosmologY), that incorporates significant improvements in our ability to model selection effects, standardization, and systematic uncertainties compared to earlier analyses. As an analysis byproduct, we also recover the posterior of the SN-only peculiar-velocity field, although we do not interpret it in this work. We compute updated cosmological constraints with Union3 and UNITY1.5, finding weak 1.7σ─2.6σ tension with flat cold dark matter and possible evidence for thawing dark energy (w0 &gt; − 1, wa &lt; 0). We release our SN distances, light-curve fits, and UNITY1.5 framework to the community.

Keywords: Cosmology, Type Ia supernovae
Where Have All the Little Red Dots Gone? Supermassive Black Hole Binary Dynamics and Its Impact on Galaxy Properties. Recent James Webb Space Telescope observations have revealed a peculiar class of galaxies at redshifts z ≳ 6, characterized by extremely high central stellar densities and overmassive central supermassive black holes (SMBHs), "little red dots" (LRDs). A critical question remains: if LRDs were common at high redshifts, how would they evolve into local elliptical galaxies with significantly lower central densities? To address this, we performed direct N-body simulations of LRD mergers, focusing on the coevolution of host galaxies and central SMBHs. We track the complete evolution of SMBH binaries into the three-body hardening and gravitational-wave (GW) emission phase. Our results demonstrate that during galaxy mergers, the central SMBHs can eject a substantial amount of mass from the galactic core via the three-body slingshot effect, leading to a decrease in central stellar surface density by an order of magnitude. Additionally, GW recoil can further contribute in making the galaxy centers less dense and more in alignment with low-redshift quiescent galaxies. This transformation occurs on a relatively short timescale of a few ∼100 Myr, implying that LRDs can evolve into lower-redshift elliptical galaxies by z &lt; 4. The timescales for our SMBH mergers vary between 100 and 800 Myr, depending on the initial orbital parameters of the merging galaxies and the mass ratio of the SMBHs. Our findings provide a plausible mechanism for the transformation of LRDs into elliptical galaxies while highlighting the efficiency of SMBH mergers in such high-density environments, which plays a crucial role in SMBH growth.

Keywords: Black hole physics
A Dormant Captured Oort Cloud Comet Awakens: (18916) 2000 OG<SUB>44</SUB>. We report the discovery of activity emanating from (18916) 2000 OG44 (alternately designated 1977 SD), a minor planet previously reported to be both an extinct comet and an asteroid on a cometary orbit. We observed 2000 OG44 with a thin tail oriented towards the coincident antisolar and antimotion vectors (as projected on the sky) in images we acquired on UT 2023 July 24 and 26 with the Apache Point Observatory 3.5 m Astrophysical Research Consortium telescope (New Mexico, USA). We also include observations made in Arizona with the Vatican Advanced Technology Telescope at the Mount Graham International Observatory and the Lowell Observatory Lowell Discovery Telescope near Happy Jack. We performed dynamical simulations that reveal 2000 OG44 most likely originated in the Oort cloud, arriving within the last 4 Myr. We find 2000 OG44, which crosses the orbits of both Jupiter and Mars, is at present on an orbit consistent with a Jupiter-family comet. We carried out thermodynamical modeling that informed our broader diagnosis that the observed activity is most likely due to volatile sublimation.

Keywords: Asteroids, Comae, Comet tails, Short period comets, Comet dynamics, Hilda group
The Receding Cosmic Shoreline of Mid-to-late M Dwarfs: Measurements of Active Lifetimes Worsen Challenges for Atmosphere Retention by Rocky Exoplanets. Detecting and characterizing the atmospheres of terrestrial exoplanets is a key goal of exoplanetary astronomy, one that may now be within reach given the upcoming campaign to conduct a large-scale survey of rocky M-dwarf worlds with the James Webb Space Telescope. It is imperative that we understand where known planets sit relative to the cosmic shoreline—the boundary between planets that have retained atmospheres and those that have not. Previous works modeled the historic X-ray and ultraviolet (XUV) radiation received by mid-to-late M-dwarf planets using a scaling relation calibrated using more massive stars, but fully convective M dwarfs display unique rotation/activity histories that differ from Sun-like stars and early M dwarfs. We synthesize observations of the active lifetimes of mid-to-late M dwarfs to present an updated estimate of their historic XUV fluence. For known planets of inactive, mid-to-late M dwarfs, we calculate a historic XUV fluence that is 2.1–3.1 times the canonical XUV scaling relation on average, with the larger value including corrections for the pre-main-sequence phase and energetic flares. We find that only the largest terrestrial planets known to orbit mid-to-late M dwarfs are likely to have retained atmospheres within the cosmic shoreline paradigm. Our calculations may help to guide the selection of targets for JWST and may prove useful in interpreting the results; to this end, we define a novel atmosphere retention metric (ARM) that indicates the distance between a planet and the cosmic shoreline, and tabulate the ARM for known mid-to-late M-dwarf planets.

Keywords: M dwarf stars, Stellar activity, Exoplanet astronomy, James Webb Space Telescope, Stellar rotation, Exoplanet atmospheres, Exoplanet atmospheric evolution
EP240414a: A Gamma-Ray Burst Jet Weakened by an Extended Circumstellar Material. The recent Einstein Probe (EP) event EP240414a exhibits several unusual observational features. Its prompt and afterglow emissions place it between long gamma-ray bursts (LGRBs) and low-luminosity GRBs (LLGRBs). The event is followed by a fast optical transient (AT 2024gsa), initially exhibiting a thermal-like spectrum but later evolving into an unusually red peak at ∼3‑5 days, which is difficult to explain with thermal emission. Using our generalized analytic framework for jet propagation in a circumstellar material (CSM), we explore a scenario in which a conventional LGRB jet is launched in a progenitor surrounded by a dense CSM. For a CSM of ∼0.03 M⊙ extending to ∼3 × 1013 cm, we find that the jet is significantly weakened before breaking out, becoming "barely failed," an intermediate state between successful (LGRB) and completely failed (LLGRB) jets. This scenario naturally explains EP240414a's multiwavelength observations, with the early thermal component produced by cocoon cooling emission and the red peak explained by nonthermal afterglow emission from the mildly relativistic barely failed jet (and its inner cocoon). Our work demonstrates the important role of extended CSM in shaping GRB jets and illustrates how early multiwavelength follow-up observations can reveal the physically diverse nature of jet-driven transients.

Keywords: Type Ic supernovae, Gamma-ray bursts, Hydrodynamics, Core-collapse supernovae, High energy astrophysics, Relativistic jets, Transient sources, Circumstellar matter, X-ray transient sources
Observations of a New Form of Partial Filament Eruption. Coronal mass ejections (CMEs) and coronal jets are two of the best-studied forms of solar eruptions, with the same underlying physics. Previous studies have presented partial eruptions producing coronal jets. We report, for the first time, a detailed analysis of three partial eruptions that segmented after the eruption began and produced CMEs. We use multiwavelength observations from the Solar Dynamics Observatory/Atmospheric Imaging Assembly, Solar TErrestrial RElations Observatory, and Solar Orbiter to reconstruct the three-dimensional evolution of the events. The magnetic field extrapolations indicated that the initial filaments were overlaid by pseudostreamer structures, and the splitting occurred after the interaction between the filament-supporting flux and external open field through their null points. The breakout mechanism seems to play a key role in both halting the system and splitting it. However, this initial evolution and the consequent splitting into an erupting flux rope above the prominence segment that failed to erupt pose severe challenges to theories of solar eruptions.

Keywords: Exoplanet atmospheric structure, Solar prominences, Solar magnetic reconnection, Solar filament eruptions
On the Origins of Coronal Alfvénic Waves. Alfvénic waves are considered a key contributor to the energy flux that powers the Sun's corona, with theoretical models demonstrating their potential to explain coronal EUV and X-ray emission and the acceleration of the solar wind. However, confirming underlying assumptions of the models has proved challenging, especially obtaining evidence for the excitation and dissipation of Alfvénic waves in the lower solar atmosphere and tracing their propagation into the corona. We present an investigation of the Alfvénic wave power spectrum in the Sun's corona, obtained from observations with DKIST Cryo-NIRSP. The data provide unprecedented temporal resolution and signal-to-noise ratio, revealing a detailed power spectrum out to frequencies exceeding 10 mHz. A broad enhancement in power dominates the spectrum, and we demonstrate that it is accurately reproduced using a physics-based model. The results corroborate the scenario where the corona is dominated by Alfvénic waves excited in the photosphere by horizontal convective motions, with low-frequency waves subject to reflection at the transition region and higher-frequency waves significantly dissipated by the partially ionized chromosphere. The coronal Alfvénic power spectrum also indicates that there are contributions from p-modes (via mode conversion) and a yet-unknown higher-frequency source. These results provide key insight into how the Sun's convective motions imprint themselves on the corona and highlight the critical role of partial ionization, reflection, and damping in regulating upward-propagating Alfvénic waves. A further implication of this is that reconnection-driven Alfvénic waves likely play a smaller role in powering the corona and solar wind than has been suggested by recent studies.

Keywords: Solar coronal waves, Magnetohydrodynamics, Alfven waves, Solar corona
Ground-based Observations of Temporal Variation of the Cosmic-Ray Spectrum during Forbush Decreases. Observations of temporary Forbush decreases (FDs) in the Galactic cosmic-ray (GCR) flux due to the passage of solar storms are useful for space-weather studies and alerts. Here, we introduce techniques that use global networks of ground-based neutron monitors and muon detectors to measure variations of GCR rigidity spectra in space during FDs by (1) fitting count rate decreases for power-law rigidity spectra in space with anisotropy up to second order and (2) using the "leader fraction" derived from a single neutron monitor. We demonstrate that both provide consistent results for hourly spectral index variations for five major FDs, and they agree with daily space-based data when available from the Alpha Magnetic Spectrometer. We have also made the neutron monitor leader fraction publicly available in real time. This work verifies that ground-based observations can be used to precisely monitor GCR spectral variation over a wide range of rigidities during space-weather events, with results in real time or from short-term postanalysis.

Keywords: Space weather, Forbush effect, Cosmic ray detectors, Solar-terrestrial interactions, Cosmic rays
ODIN: Star Formation Histories Reveal Formative Starbursts Experienced by Lyα-emitting Galaxies at Cosmic Noon. In this work, we test the frequent assumption that Lyα-emitting galaxies (LAEs) are experiencing their first major burst of star formation at the time of observation. To this end, we identify 74 LAEs from the ODIN Survey with rest-UV-through-NIR photometry from UVCANDELS. For each LAE, we perform nonparametric star formation history (SFH) reconstruction using the Dense Basis Gaussian-process-based method of spectral energy distribution fitting. We find that a strong majority (67%) of our LAE SFHs align with the frequently assumed archetype of a first major star formation burst, with at most modest star formation rates (SFRs) in the past. However, the rest of our LAE SFHs have significant amounts of star formation in the past, with 28% exhibiting earlier bursts of star formation, with the ongoing burst having the highest SFR (dominant bursts) and the final 5% having experienced their highest SFR in the past (nondominant bursts). Combining the SFHs indicating first and dominant bursts, ∼95% of LAEs are experiencing their largest burst yet: a formative burst. We also find that the fraction of total stellar mass created in the last 200 Myr is ∼1.3 times higher in LAEs than in mass-matched Lyman break galaxy (LBG) samples, and that a majority of LBGs are experiencing dominant bursts, reaffirming that LAEs differ from other star-forming galaxies. Overall, our results suggest that multiple evolutionary paths can produce galaxies with strong observed Lyα emission.

Keywords: Galaxy formation, Star formation, Spectral energy distribution, Galaxy evolution, Lyman-alpha galaxies
Ice Sublimation in the Dynamic HD 100453 Disk Reveals a Rich Reservoir of Inherited Complex Organics. Protoplanetary disks around luminous young A-type stars are prime observational laboratories to determine the abundances of complex organic molecules (COMs) present during planet formation. In contrast to their lower stellar mass counterparts, these warmer disks contain the sublimation fronts of complex molecules such as CH3OH on spatial scales accessible with the Atacama Large Millimeter/submillimeter Array (ALMA). We present ALMA observations of the Herbig Ae disk HD 100453 that uncover a rich reservoir of COMs sublimating from the dust cavity edge. In addition to CH3OH, we detect 13CH3OH for the first time in a Class II disk, revealing a factor of three enhancement of 13C in the disk large organics. A tentative detection of CH2DOH is also reported, resulting in a D/H of 1%─2%, which is consistent with the expected deuterium enhancement from the low-temperature CH3OH formation in molecular clouds and with the deuteration of CH3OH measured in comets. The detection of methyl-formate (CH3OCHO), at only a few percent level of CH3OH, is an order of magnitude lower compared to claims toward other organic-rich Herbig Ae disks but is more in line with organic abundance patterns toward the earlier stages of star formation. Together these data provide multiple lines of evidence that disks, and therefore the planet- and comet-forming materials, contain inherited interstellar ices and perhaps the strongest evidence to date that much of the interstellar organic ice composition survives the early stages of planet formation.

Keywords: Radio astronomy, Protoplanetary disks, Complex organic molecules, Astrochemistry
3D Simulations Demonstrate Propagating Thermohaline Convection for Polluted White Dwarfs. Polluted white dwarfs (WDs) with small surface convection zones deposit significant concentrations of heavy elements to the underlying radiative interior, presumably driving thermohaline convection. Current models of polluted WDs frequently fail to account for this effect, although its inclusion can increase the inferred accretion rate by orders of magnitude. It has been argued that this instability cannot be treated as a continuous mixing process and thus should not be considered in these models. In this work, we study 3D simulations of a thermohaline-unstable layer propagating into an underlying stable region, approximating the polluted WD scenario. We find that although thermohaline convection works to reduce driving gradients somewhat, the front continues to propagate and the system remains unstable. Importantly, the turbulent flux of metals broadly dominates over the diffusive flux in quantitative agreement with existing mixing prescriptions implemented in some stellar evolution models (except slightly below the boundary of the propagating front, where recent prescriptions neglect overshoot-like effects). Thus, our results broadly support polluted WD models that include thermohaline mixing in their estimates of the settling rate.

Keywords: White dwarf stars, Astrophysical fluid dynamics, DA stars
Hints of Disk Substructure in the First Brown Dwarf with a Dynamical Mass Constraint. We present high-resolution Atacama Large Millimeter/submillimeter Array (ALMA) observations at 0.89 mm of the Class II brown dwarf 2MASS J04442713+2512164 (2M0444), achieving a spatial resolution of 0 .″ 046 (∼6.4 au at the distance to the source). These observations targeted continuum emission together with 12CO (3–2) molecular line. The line emission traces a Keplerian disk, allowing us to derive a dynamical mass between 0.043 and 0.092 M⊙ for the central object. We constrain the gas-to-dust disk size ratio to be ∼7, consistent with efficient radial drift. However, the observed dust emission suggests that a dust trap is present, enough to retain some dust particles. We perform visibility fitting of the continuum emission, and under the assumption of annular substructure, our best fit shows a gap and a ring at 98.1 ‑8.4+4.2  mas (∼14 au) and 116.0 ‑4.8+4.2  mas (∼16 au), respectively, with a gap width of 20 mas (∼3 au). To ensure robustness, the data were analyzed through a variety of methods in both the image and uv planes, employing multiple codes and approaches. This tentative disk structure could be linked to a possible planetary companion in the process of formation. These results provide the first dynamical mass of the lowest mass object to date, together with the possible direct detection of a substructure, offering new insights into disk dynamics and planet formation in the very low-mass regime. Future higher spatial resolution ALMA observations will be essential to confirm these findings and further investigate the link between substructures and planet formation in brown dwarf disks.

Keywords: Brown dwarfs, Millimeter astronomy, Protoplanetary disks, Submillimeter astronomy, Circumstellar dust, Radio interferometry, Planet formation
Satellite Formation around the Largest Asteroids. Satellites around large asteroids are preferentially found among those with the most rapid rotation and elongated shape. The taxonomic statistics are similarly skewed; in total, 13 asteroids larger than 100 km are known to have satellites, but none have been discovered among S-type asteroids. Previous modeling suggests that satellites could be generated by impacts, but spin and shape have never been tracked in models to relate collisional circumstances with those two observed properties concerning the primary. Here we show, by combining simulations of impacts into porous low-density asteroids, their subsequent disruption, reaccumulation, and long-term satellite stability, a direct pathway for the formation of satellites. The immediate distortion and elongation of a rotating target body provide a launching point for some debris distinct from simple ballistic ejecta trajectories. The debris that are found to originate from the distorted long axis is sourced primarily from 10 to 20 km below the surface and can be placed directly onto eccentric orbits with sufficiently large pericenter distances that avoid rapid reimpact. The specific energy and resultant total mass loss in satellite-forming collisions are not constraining, which explains the observed lack of correlation between asteroids with satellites and those that are part of large asteroid families.

Keywords: Asteroid satellites, Main belt asteroids