Sazuna/UAT_keywords huggingface dataset:
Early Emission from Double Detonation Type Ia Supernovae. A popular model for Type Ia supernovae is the detonation of a CO white dwarf that is triggered by the prior detonation of a thin surface layer of helium, known as a double detonation (DD). We explore the unique early electromagnetic signatures that are expected from the collision of the CO detonation with the He detonation. The three features are (1) a shock breakout flash, (2) a stage of planar shock breakout cooling, and finally, (3) shock cooling emission from the thermal energy released by the collision. The planar phase is unique to the unusual density profile of the He-detonated layer in comparison to the steep profile at a stellar edge, as is usually considered for shock breakout. The shock cooling emission can be modified by recombination, and we explore these effects. Altogether, we expect an initial flash dominated by the planar phase of ∼6 × 1043 erg s−1, which lasts ∼5 s in the soft X-rays. This is followed by ∼12─24 hr of shock cooling at a luminosity of 3─10 × 1040 erg s−1 in the optical/UV. We discuss prospects for the detection of this early DD emission with current and upcoming surveys.

Keywords: White dwarf stars, Type Ia supernovae, Supernovae, Hydrodynamics
Orbital and Pulsation Analysis of 42 Heartbeat Stars Discovered in TESS Data. Heartbeat stars (HBSs) are ideal laboratories for studying the formation and evolution of binary stars in eccentric orbits and their mutual tidal interactions. We present 42 new HBSs discovered based on Transiting Exoplanet Survey Satellite Science Processing Operations Center (TESS-SPOC) and Quick-Look Pipeline data. Their physical parameters have been obtained through modeling with appropriate models. Subsequently, tidally excited oscillations (TEOs) are detected in 10 systems, and their pulsation phases and modes are identified. Most pulsation phases can be explained by the dominant being spherical harmonic degree l = 2 and azimuthal order m = 0 or ±2. For TIC 156846634, the harmonic with large deviation (&gt;3σ) from the expected adiabatic phase can be expected to be a traveling wave or significantly nonadiabatic. The harmonic numbers n = 16 in TIC 184413651 may not be considered as a TEO candidate due to its large deviation (&gt;2σ) from the adiabatic expectation. Moreover, TIC 92828790 shows no TEOs but exhibits a significant gamma Doradus─type pulsation. The eccentricity─period relation also shows a positive correlation between eccentricity and period, as well as the existence of orbital circularization. The Hertzsprung─Russell diagram shows that TESS HBSs have higher temperatures and greater luminosities than Kepler HBSs, possibly due to selection effects. This significantly enhances the detectability of massive HBSs and those containing TEOs.

Keywords: Stellar oscillations, Elliptical orbits, Binary stars, Pulsating variable stars
Consistent Gas-phase C/O Abundances from UV and Optical Emission Lines: A Robust Scale for Chemical Evolution across Cosmic Time. The carbon-to-oxygen (C/O) abundance ratio is a valuable tracer of star formation history, as C and O enrichment occurs on different timescales. However, measurements based on ultraviolet (UV) collisionally excited lines and those based on optical recombination lines may be subject to biases from the abundance discrepancy factor (ADF), which is well established for oxygen but uncertain for carbon. We present precise UV-based measurements of gas-phase C2+/O2+ ionic abundance in four H II regions, which have prior optical-based measurements, combined with archival UV data for two additional H II regions, in order to establish a reliable abundance scale and to investigate biases between the two methods. We find a clear ADF for the C2+ ion, which is consistent with that of O2+, assuming a similar temperature structure in the zones of the nebula that these ions occupy. The C/O abundance derived from UV collisional lines and optical recombination lines is therefore also consistent to within &lt;0.1 dex, with an offset of 0.05 ± 0.03 dex in C2+/O2+ for the standard Te method. While the absolute C/H and O/H abundances are subject to large uncertainty from the ADF, our results establish that C/O abundances measured from these different methods can be reliably compared. Thus, we confirm the robustness of gas-phase C/O measurements for studying galaxy evolution and star formation timescales, including from rest-UV observations of high-redshift galaxies with JWST.

Keywords: Galaxy chemical evolution, H II regions, Chemical abundances, Interstellar medium
Electrostatic Field Formed by Charge Separation in Magnetic Reconnection with a Guide Field. The formation of charge separation in antiparallel magnetic reconnection has previously been investigated in S. Hu et al., and the results show that the charge separation arises from the combined effects of the parallel electron flux and the changes in the geometric dimensions of the magnetic flux tube. In this paper, using a 2.5-dimensional particle-in-cell simulation, we characterized the properties of charge separation in guide field magnetic reconnection and conducted a quantitative analysis on how these effects alter the formation of charge separation. In guide field magnetic reconnection, the charge separation develops in the separatrix region: the upper-right and lower-left subregions exhibit positive charge density, whereas the upper-left and lower-right subregions exhibit negative charge density, or conversely, depending on the guide field direction. Under a sufficiently strong guide field, the effect of the geometric dimensions of the flux tube becomes negligible, and the charge separation is dominated by the parallel electron flux. As electrons flow into the vicinity of the X-line along the separatrix in the upper-right and lower-left regions, the parallel electron flux increases. This leads to a negative net flux of electrons, thereby causing positive charge accumulation. Similarly, as electrons flow out of the vicinity of the X-line along the separatrix in the upper-left and lower-right regions, the parallel electron flux decreases, thereby causing negative charge accumulation. Additionally, as the guide field weakens, the effect of the geometric dimensions of the flux tube becomes increasingly significant, and charge separation gradually transforms into the distribution observed in antiparallel magnetic reconnection.

Keywords: Space plasmas, Planetary magnetospheres, Plasma physics
A Preinfall Magellanic Analog─Corona and Stream Formation in the HESTIA Cosmological Simulations. We identify and investigate a preinfall analog of the Large and Small Magellanic Clouds (LMCs, SMCs) in the High-Resolution Environmental Simulations of the Immediate Area suite of constrained cosmological simulations. The system, dynamically isolated from the Local Group, evolves over ∼6 Gyr and forms a multiphase warm coronal halo and a neutral gas stream via repeated tidal interactions, ∼150 kpc in length. The LMC analog's corona forms self-consistently through virial accretion and inhibits the survival of clumpy neutral structures beyond ∼600 Myr. The SMC analog remains bound through to z = 0, and the pair also exhibits bridge-like and leading-arm features. These results suggest that while most of the ionized stream is formed by the LMC coronal gas, the neutral gas stream, bridge, and leading arm components of the Magellanic System can arise from dwarf─dwarf interactions prior to infall, while the survival and ionization of these features likely require additional environmental processing. Furthermore, we identify a stellar component out of phase to the neutral component of the stream, implying that if the Magellanic stellar stream exists, it may not be spatially coexistent to the dominant H I stream. This system offers a valuable preinfall reference point for interpreting the Magellanic System and identifying analogs beyond the Local Group.

Keywords: Galaxy structure, Magellanic Stream, Circumgalactic medium, Magellanic Clouds, Magnetohydrodynamical simulations
Constraining the Neutron-star Equation of State via Short Gamma-Ray Burst X-Ray Afterglows. Recent observations from NICER in X-rays and LIGO/Virgo in gravitational waves have provided critical constraints on the mass, radius, and tidal deformability of neutron stars, imposing stringent limits on the equation of state (EOS) and the behavior of ultradense matter. However, several key parameters influencing the EOS, such as the maximum mass of neutron stars, spin-down rates, and the potential role of exotic matter in their cores, remain the subject of ongoing debate. Here we present a new approach to constraining the EOS by analyzing the X-ray afterglows of some short gamma-ray bursts, focusing on "the internal plateau" phase and its abrupt decay, which reflect the spin-down and possible collapse of a supramassive neutron star into a black hole. By linking critical neutron star masses with black hole formation criteria and the observational data from Swift's Swift's Burst Alert Telescope (BAT) and X-Ray Telescope (XRT) with compact object models, we explore three representative EOSs that range from "soft" to "stiff." Our result supports a maximum mass for neutron stars of approximately 2.39 solar masses at the threshold of black hole formation. This conclusion holds under assumptions of magnetar-powered X-ray plateaus, constant radiative efficiency, isotropic emission, and full Kerr black hole energy extraction; deviations could influence the inferred results. Our results demonstrate the critical role of neutron star/black hole physics in probing dense nuclear matter and provide a novel framework for exploring extreme astrophysical environments.

Keywords: Neutron stars, Gamma-ray bursts, Black holes
Constraints on the Orbit of the Young Substellar Companion GQ Lup B from High-resolution Spectroscopy and VLTI/GRAVITY Astrometry. Understanding the orbits of giant planets is critical for testing planet formation models, particularly at wide separations (&gt;10 au) where traditional core accretion becomes inefficient. However, constraining orbits at these separations has historically been challenging due to sparse orbital coverage and related degeneracies in the orbital parameters. In this work, we use existing high-resolution (R ∼ 100,000) spectroscopic measurements from CRIRES+, astrometric data from SPHERE, NACO, and Atacama Large Millimeter/submillimeter Array, and combine it with new high-precision GRAVITY astrometry data to refine the orbit of GQ Lup B, a ∼30 MJ companion at ∼100 au, in a system that also hosts a circumstellar disk and a wide companion, GQ Lup C. Including radial velocity (RV) data significantly improves orbital constraints by breaking the degeneracy between inclination and eccentricity that plagues astrometry-only fits for long-period companions. Our work is one of the first to combine high-precision astrometry with the companion's relative radial velocity measurements to achieve significantly improved orbital constraints. The eccentricity is refined from  e=0.47−0.16+0.14  (GRAVITY only) to  e=0.35−0.09+0.10  when RVs and GRAVITY data are combined. We also compute the mutual inclinations between the orbit of GQ Lup B, the circumstellar disk, the stellar spin axis, and the disk of GQ Lup C. The orbit is misaligned by  63−14+6 ° relative to the circumstellar disk,  52−24+19 ° with the host star's spin axis, but appears more consistent ( 34−13+6 °) with the inclination of the wide tertiary companion GQ Lup C's disk. These results support a formation scenario for GQ Lup B consistent with cloud fragmentation. They highlight the power of combining companion RV constraints with interferometric astrometry to probe the dynamics and formation of wide-orbit substellar companions. *Based on observations collected at the European Southern Observatory under ESO programmes 1104.C-0651 and 109.238N.001.

Keywords: Orbits, Exoplanet formation
First Direct Carbon Abundance Measured at z &gt; 10 in the Lensed Galaxy MACS0647-JD. Investigating the metal enrichment in the early Universe helps us constrain theories about the first stars and study the ages of galaxies. The lensed galaxy MACS0647−JD at z = 10.17 is the brightest galaxy known at z &gt; 10. Previous work analyzing JWST NIRSpec and MIRI data yielded a direct metallicity  12+log(O/H)=7.79±0.09  (∼0.13 Z⊙) and electron density  log(ne/cm−3)=2.9±0.5 , the most distant such measurements to date. Here we estimate the direct C/O abundance for the first time at z &gt; 10, finding a subsolar  log(C/O)=−0.44−0.07+0.06 . This is higher than other z &gt; 6 galaxies with direct C/O measurements, likely due to higher metallicity. It is also slightly higher than galaxies in the local Universe with similar metallicity. This may suggest a very efficient and rapid burst of star formation, a low effective oxygen abundance yield, or the presence of unusual stellar populations, including supermassive stars. Alternatively, the strong C III] λλ1907,1909 emission (14 ± 3 Å rest-frame equivalent width may originate from just one of the two component star clusters JDB (r ∼ 20 pc). Future NIRSpec integral field unit spectroscopic observations of MACS0647−JD will be promising for disentangling C/O in the two components to constrain the chemistry of individual star clusters just 460 Myr after the Big Bang.

Keywords: Early universe, Metallicity, Population III stars, Chemical abundances, Galaxy spectroscopy, High-redshift galaxies, Galaxies
Investigating Variations in Solar Differential Rotation by Helioseismology. Helioseismic signatures of dynamo waves have recently been discovered in variations of the solar differential rotation, offering valuable insights into the type of dynamo mechanism operating in the solar convection zone. To characterize these variations, we analyze p-mode frequency-splitting data estimated using time intervals of various lengths to enhance the signal-to-noise ratio in inversions of zonal flows. We introduce a novel time-dependent inversion method that inherently smooths the solution over time, eliminating the need for separate post-processing smoothing. By applying this approach to observational data from the Michelson Doppler Imager onboard the Solar and Heliospheric Observatory, Helioseismic and Magnetic Imager onboard the the Solar Dynamics Observatory, and Global Oscillation Network Group, we identify similar dynamo wave patterns in both the zonal acceleration and the zonal flow throughout the entire convection zone. Our analysis shows that while using longer time series smooths out temporal variations, the fundamental features observed in the short time series (i.e., 72 days long) persist when inverting data sets covering different time periods. These findings reinforce earlier detections and offer further validation of solar dynamo models. We additionally investigate the dimensionless radial gradient of rotation. Its value is close to −1 and increases in the deeper layers, remaining nearly constant from the equator to midlatitudes within the depth range of 13─35 Mm below the surface; the results at high latitudes remain somewhat inconclusive. The variation of this quantity displays a torsional oscillation-like pattern, albeit with certain differences.

Keywords: Solar cycle, Solar differential rotation, Solar interior, Helioseismology, Solar dynamo, Solar physics, Solar magnetic fields
Evolution of the Physical Properties of the Most Massive Galaxies in Clusters and Their Protohalos. We investigated the evolution of the physical properties of the brightest galaxies in clusters and their protohalos from z = 4 to z = 0. Galaxy clusters and groups are identified using a halo-based group finder applied to the COSMOS2020 galaxy catalog. We construct evolution chains from low redshift clusters to higher redshift groups via the abundance matching method. The region of protohalos corresponding to clusters is defined on the basis of a characteristic radius. Our analysis encompasses a wide range of physical properties, including stellar mass, luminosity, star formation rate, specific star formation rate, color (g − r), and stellar age. The evolution trends of the most massive galaxies (MMGs) in higher redshift groups and their corresponding protohalos are generally consistent. The stellar mass of MMGs shows an increasing trend across the entire redshift range. By considering the stellar mass growth as in situ and ex situ components, we find that in situ star formation is efficient at z ∼ 2, while ex situ accretion becomes the primary growth channel at later times. At z ≳ 2, MMGs undergo an intense star formation phase of approximately 102 M⊙ yr−1, but are generally quenched at lower redshifts. Stellar age analysis suggests that most stars in MMGs formed at z &gt; 2. Our results present a coherent picture of MMG evolution across cosmic epochs, which is broadly consistent with the current theoretical framework of galaxy formation and evolution. Moreover, our work provides an intriguing way to trace galaxy evolution through the construction of cluster evolutionary chains in observations.

Keywords: Galaxy clusters, Galaxy dark matter halos, Protoclusters, Galaxy groups, Galaxy evolution, Dark matter, Galaxies
Electron Acceleration in Magnetic Reconnection-driven Turbulence in the Earth's Magnetotail. The Magnetospheric Multiscale mission has identified regions of magnetic reconnection surrounded by strong turbulence associated with particle acceleration in the Earth's magnetotail. In these turbulent reconnection regions, ion and electron distributions have substantially elevated temperatures and display nonthermal tails indicating acceleration to over ∼100 times their initial thermal energies. We investigate electron energization and acceleration using 3D test-particle simulations based on the measured magnetic and electric fields in a representative magnetic reconnection geometry. We explore stochastic, Fermi, betatron, Speiser, and turbulence-boosted Speiser-like energization and acceleration. We find that stochastic energization and Speiser-like motion (Speiser orbits and turbulence-boosted Speiser-like orbits) dominate energization and acceleration at high turbulence levels and make the largest contribution to the nonthermal tail. Electron energization comes mostly from second-order impulses from electric fields with frequencies above the ion cyclotron frequency. Perpendicular electric fields contribute to the majority of the energization (∼75%). However, the exiting electron fluxes show the reverse; most (∼62%) of the electron energy flux exits as parallel energy. Trapping in the low magnetic field near the magnetic reconnection current sheet plays an important role by increasing dwell time in the turbulence, which enhances stochastic and Speiser-like processes. One of our primary conclusions is that magnetic reconnection and turbulence appear to combine as an efficient accelerator; the turbulent acceleration near a magnetic reconnection current sheet favors high-energy electrons, generating the energetic tail. Given its widespread presence in space and astrophysical plasmas, turbulent magnetic reconnection should be considered an important source of accelerated electrons.

Keywords: Planetary magnetospheres, Interplanetary particle acceleration, Plasma astrophysics
Unveiling a New β Scaling of the Tearing Instability in Weakly Collisional Plasmas. We investigate the linear tearing instability in weakly collisional plasmas using a nonideal gyrotropic MHD framework, uncovering a previously unknown scaling relation for the instability growth rate in high-β environments. Even starting from an isotropic equilibrium, our analysis reveals a β-dependence, with the maximum growth rate scaling as  σmaxτa∝β−1/4 , challenging the long-held assumption of β-independence inherent in classical MHD formulations. This novel scaling emerges due to self-consistent fluctuations in pressure anisotropy, dynamically induced by perturbations in velocity and magnetic fields. Increasing plasma-β always suppresses the instability, whereas a background pressure anisotropy can either enhance or further suppress it, depending on its sign: for p∥,0 &lt; p⊥,0, the instability is strengthened, while for p∥,0 &gt; p⊥,0, it is weakened. Importantly, this effect is not limited to low-collisionality plasmas at high β; it can also manifest in more collisional environments once the strict assumption of pressure isotropy is relaxed. This finding has profound implications for various astrophysical contexts characterized by high β and varying degrees of collisionality, including the solar corona and heliospheric current sheets, planetary magnetospheres as probed by space missions, and the intracluster medium, where magnetic reconnection critically impacts magnetic field evolution and cosmic-ray transport. Our results therefore question the universality of the widely accepted plasmoid-mediated fast reconnection paradigm and underscore the necessity of incorporating pressure anisotropy effects into reconnection models for accurate representation of astrophysical plasmas.

Keywords: Cosmology, Space plasmas, Solar magnetic reconnection, Plasma astrophysics, Solar physics, Interstellar medium, Intracluster medium
Bridging Machine Learning and Spectroscopy: A New Analysis for Astrochemical Target Selection. In the last few years, several approaches have used machine learning to reproduce the inventory and column densities of interstellar molecular sources. These models can also provide predictions of other molecules that might make good targets for discovery in a source, along with a predicted column density. A molecular target and column density alone are often not enough to dictate a good target; spectroscopic considerations (e.g., permanent electric dipole moments, line intensities, and line frequencies) need to be accounted for as well. Here we describe a new approach to take these considerations into account, in an attempt to identify the hidden likely candidates among thousands of molecules and associated column densities recommended by machine learning. We leverage machine learning results alongside quantum chemical and astronomical considerations to define a "detectability" metric and then apply this analysis to machine learning─recommended molecules in TMC─1. We find that this approach significantly narrows the field of candidate species but also highlights some of the ongoing issues with results from machine learning models trained on the very small (for machine learning) data sets produced by observations. We discuss these in the context of the need for human intervention, finding that our approach reduces but certainly does not eliminate this requirement.

Keywords: Computational methods, Astronomy data analysis, Star forming regions, Astrochemistry
A Search for Minute-timescale Flares from the Transient AT 2024wpp. The AT 2018cow-like fast blue optical transient AT 2022tsd showed a large number of a few-minute-duration, high-luminosity (∼1043 erg s−1) flares. We present an intensive search for such flares from another 18cow-like event, AT 2024wpp. We have used the Large Array Survey Telescope to observe this transient between 28 and 74 days after the approximate time of zero flux. The target was observed for about 23 hr to a sensitivity that allows one to detect 3 × 1042 erg s−1 flares at a signal-to-noise ratio ≳ 5. No optical flares have been found, suggesting a one-sided 2σ confidence upper limit of &lt;0.02 on the flare's duty cycle, and flare rate lower than about 0.11 hr−1. These limits suggest that not all 18cow-like objects display a high rate of minute-timescale luminous flares. This can be explained either by diversity in the 18cow-like population or by viewing angle effects (e.g., beaming), or rather that the optical depth toward the central emitting region did not fall below unity during the particular search window.

Keywords: Supernovae, Photometry