adsabs/SciX_UAT_keywords huggingface dataset:
When Do Stars Go Boom?

The maximum mass of a star that can produce a white dwarf (WD) is an important astrophysical quantity. One of the best approaches to establishing this limit is to search for WDs in young star clusters in which only massive stars have had time to evolve and where the mass of the progenitor can be established from the cooling time of the WD together with the age of the cluster. Searches in young Milky Way clusters have not thus far yielded WD members more massive than about 1.1 M ⊙, well below the Chandrasekhar mass of 1.38 M ⊙, nor progenitors with masses in excess of about 6 M ⊙. However, the hunt for potentially massive WDs that escaped their cluster environs is yielding interesting candidates. To expand the cluster sample further, we used HST to survey four young and massive star clusters in the Magellanic Clouds for bright WDs that could have evolved from stars as massive as 10 M ⊙. We located five potential WD candidates in the oldest of the four clusters examined, the first extragalactic single WDs thus far discovered. As these hot WDs are very faint at optical wavelengths, final confirmation will likely have to await spectroscopy with 30 m class telescopes.

Keywords: white dwarf stars; open star clusters; stellar evolution; chandrasekhar limit
Testing the Alfvén-wave Model of the Solar Wind with Interplanetary Scintillation

Understanding the mechanism(s) of solar wind acceleration is important in astrophysics and geophysics. A promising model of solar wind acceleration is known as the wave/turbulence-driven (WTD) model, in which Alfvén waves feed energy to the solar wind. In this study, we tested the WTD model with global measurements of wind speed from interplanetary scintillation (IPS) observations. For Carrington rotations in minimal and maximal activity phases, we selected field lines calculated by the potential-field source-surface method in high and midlatitudes and compared the simulated and observed wind velocities. The simulation was performed in a self-consistent manner by solving the magnetohydrodynamic equations from the photosphere to the solar wind. In high-latitude regions, the simulated solar wind velocity agrees better with the IPS observation than with the classical Wang-Sheeley empirical estimation, both in maximal and minimal activity phases. In midlatitude regions, the agreement worsens, possibly because of the inaccuracy of the WTD model and/or the magnetic-field extrapolation. Our results indicate that the high-latitude solar wind is likely to be driven by waves and turbulence and that the physics-based prediction of the solar wind velocity is highly feasible with an improved magnetic-field extrapolation.

Keywords: interplanetary physics; solar wind; magnetohydrodynamical simulations; alfven waves
A New Period Determination Method for Periodic Variable Stars

Variable stars play a key role in understanding the Milky Way and the universe. The era of astronomical big data presents new challenges for quick identification of interesting and important variable stars. Accurately estimating the periods is the most important step to distinguish different types of variable stars. Here, we propose a new method of determining the variability periods. By combining the statistical parameters of the light curves, the colors of the variables, the window function and the Generalized Lomb-Scargle (GLS) algorithm, the aperiodic variables are excluded and the periodic variables are divided into eclipsing binaries and NEB variables (other types of periodic variable stars other than eclipsing binaries), the periods of the two main types of variables are derived. We construct a random forest classifier based on 241,154 periodic variables from the ASAS-SN and OGLE data sets of variables. The random forest classifier is trained on 17 features, among which 11 are extracted from the light curves and 6 are from the Gaia Early DR3, ALLWISE, and 2MASS catalogs. The variables are classified into 7 superclasses and 17 subclasses. In comparison with the ASAS-SN and OGLE catalogs, the classification accuracy is generally above approximately 82% and the period accuracy is 70%-99%. To further test the reliability of the new method and classifier, we compare our results with the results of Chen et al. for ZTF DR2. The classification accuracy is generally above 70%. The period accuracy of the EW and SR variables is ~50% and 53%, respectively. And the period accuracy of other types of variables is 65%-98%.

Keywords: light curve classification; period determination; periodic variable stars
A Tight Universal Relation between the Shape Eccentricity and the Moment of Inertia for Rotating Neutron Stars

Universal relations that are insensitive to the equation of state are useful in reducing the parameter space when measuring global quantities of neutron stars (NSs). In this paper, we reveal a new universal relation that connects the eccentricity to the radius and moment of inertia of rotating NSs. We demonstrate that the universality of this relation holds for both conventional NSs and bare quark stars (QSs) in the slow-rotation approximation, albeit with different relations. The maximum relative deviation is approximately 1% for conventional NSs and 0.1% for QSs. Additionally, we show that the universality still exists for fast-rotating NSs if we use the dimensionless spin to characterize their rotation. The new universal relation will be a valuable tool to reduce the number of parameters used to describe the shape and multipoles of rotating NSs, and it may also be used to infer the eccentricity or moment of inertia of NSs in future X-ray observations.

Keywords: neutron stars
Formation of the Cosmic-Ray Halo: Galactic Spectrum of Primary Cosmic Rays

A self-consistent model of a one-dimensional cosmic-ray (CR) halo around the Galactic disk is formulated with the restriction of a minimum number of free parameters. It is demonstrated that the turbulent cascade of MHD waves does not necessarily play an essential role in the halo formation. Instead, an increase of the Alfvén velocity with distance to the disk leads to an efficient generic mechanism of the turbulent redshift, enhancing CR scattering by the self-generated MHD waves. As a result, the calculated size of the CR halo at lower energies is determined by the halo sheath, an energy-dependent region around the disk beyond which the CR escape becomes purely advective. At sufficiently high energies, the halo size is set by the characteristic thickness of the ionized gas distribution. The calculated Galactic spectrum of protons shows a remarkable agreement with observations, reproducing the position of the spectral break at $\approx 0.6$ TeV and the spectral shape up to ∼10 TeV.

Keywords: galactic cosmic rays; high energy astrophysics; alfven waves
Stellar-reddening-based Extinction Maps for Cosmological Applications

Cosmological surveys must correct their observations for the reddening of extragalactic objects by Galactic dust. Existing dust maps, however, have been found to have spatial correlations with the large-scale structure of the Universe. Errors in extinction maps can propagate systematic biases into samples of dereddened extragalactic objects and into cosmological measurements such as correlation functions between foreground lenses and background objects and the primordial non-Gaussianity parameter f NL. Emission-based maps are contaminated by the cosmic infrared background, while maps inferred from stellar reddenings suffer from imperfect removal of quasars and galaxies from stellar catalogs. Thus, stellar-reddening-based maps using catalogs without extragalactic objects offer a promising path to making dust maps with minimal correlations with large-scale structure. We present two high-latitude integrated extinction maps based on stellar reddenings, with a point-spread functions of FWHMs 6.'1 and 15'. We employ a strict selection of catalog objects to filter out galaxies and quasars and measure the spatial correlation of our extinction maps with extragalactic structure. Our galactic extinction maps have reduced spatial correlation with large-scale structure relative to most existing stellar-reddening-based and emission-based extinction maps.

Keywords: interstellar extinction; large-scale structure of the universe
A Unified Framework for Manipulating N-dimensional Astronomical Data and Coordinate Transformations in Python: The NDCube 2 and Astropy APE-14 World Coordinate System APIs

The NDCube 2 API is a Python application programming interface (API) for storing and manipulating N-dimensional coordinate-aware astronomical data. While there are Python packages for handling astronomical data and coordinate transformations separately and for handling specific combinations of dimensions and transformations, none provide a unified and agnostic way of handling them simultaneously. This leads to a proliferation of different APIs for conducting the same analysis tasks on similar types of observations and introduces technical barriers between multi-instrument studies and cross-community collaboration. In this paper, we outline how the NDCube 2 API and its implementation in the open-source, community-developed ndcube package, together with the AstroPy WCS API, help to solve this problem. We discuss the guiding principles underpinning the API design and provide examples of how it is already being used to serve broad sections of the astronomy community, including agency-funded missions. The aim of this paper is to help users better understand the purpose and potential of the NDCube 2 API and ndcube package and hence how to more effectively deploy them in scientific analyses and software development.

Keywords: astronomy data analysis; astronomical coordinate systems; astronomy software; open source software; distributed computing; gpu computing
The Interaction of Type Iax Supernova Ejecta with a Helium Companion Star

Type Iax supernovae (SNe Iax) are an important subluminous class of SNe Ia. However, their progenitors and explosion mechanisms are not yet understood. It has been suggested that SNe Iax may be produced from weak deflagration explosions of Chandrasekhar-mass white dwarfs (WDs) in binary systems with a helium (He) star donor. In such progenitor systems, the stripped He companion material caused by the ejecta-companion interaction is expected to present some He features in their late-time spectra. However, the detection of He lines in late-time spectra of SNe Iax has not yet been successful, which gives an upper limit on the amount of stripped He mass of $\lesssim 2\times {10}^{-3}-0.1$ ${M}_{\odot }$ . In this work, we study the interaction between SN Iax ejecta and a He star companion by performing three-dimensional hydrodynamical simulations with a weak pure deflagration explosion model. We find that about $4\times {10}^{-3}$ ${M}_{\odot }$ of He material can be stripped off from the companion star by SN explosion, which is very close to (or lower than) the observational upper limit on the total stripped He mass in SNe Iax. We, therefore, conclude that nondetection of He lines in late-time spectra of SNe Iax could be reasonably explained if they indeed resulted from weak pure deflagration explosions of Chandrasekhar-mass WDs in progenitor systems with a He star donor.

Keywords: type ia supernovae; hydrodynamical simulations; close binary stars; chandrasekhar limit
Role of Magnetic Fields in Fueling Seyfert Nuclei

Molecular gas is believed to be the fuel for star formation and nuclear activity in Seyfert galaxies. To explore the role of magnetic fields in funneling molecular gas into the nuclear region, measurements of the magnetic fields embedded in molecular gas are needed. By applying the new velocity gradient technique (VGT) to CO isotopolog data from the Atacama Large Millimeter/submillimeter Array and the Plateau de Bure Interferometer Arcsecond Whirlpool Survey, we obtain the first detection of CO-associated magnetic fields in several nearby Seyfert galaxies and their unprecedented high-resolution magnetic field maps. The VGT-measured magnetic fields in molecular gas globally agree with those inferred from existing HAWC+ dust polarization and Very Large Array synchrotron polarization. An overall good alignment between the magnetic fields traced by VGT-CO and by synchrotron polarization may support the correlation between star formation and cosmic-ray generation. We find that the magnetic fields traced by VGT-CO have a significant radial component in the central regions of most Seyferts in our sample, where efficient molecular gas inflows or outflow may occur. In particular, we find local misalignment between the magnetic fields traced by CO and dust polarization within the nuclear ring of NGC 1097, and the former aligns with the central bar's orientation. This misalignment reveals different magnetic field configurations in different gas phases and may provide an observational diagnostic for the ongoing multiphase fueling of Seyfert activity.

Keywords: extragalactic magnetic fields; interstellar medium; galaxy nuclei; interstellar synchrotron emission
No Rotational Variability in C/2014 UN271 (Bernardinelli-Bernstein) at 23.8 au and 21.1 au as Seen by TESS

The recent discovery of a hundred-kilometer-scale comet, C/2014 UN271 (Bernardinelli-Bernstein), has provoked interest in the activity displayed by such a large body inbound from the Oort cloud. We examine the serendipitous observation of UN271 in long-cadence imaging by the TESS satellite in 2018 and 2020, while Bernardinelli-Bernstein was at 23.8 and 21.3 au, for any notable periodicity. Bernardinelli-Bernstein does not display detectable rotational variability above the noise level in these data.

Keywords: comets
Compact Molecular Gas Distribution in Quasar Host Galaxies

We use Atacama Large Millimeter/submillimeter Array CO (2-1) observations of six low-redshift Palomar-Green quasars to study the distribution and kinematics of the molecular gas of their host galaxies at kiloparsec-scale resolution. While the molecular gas content, molecular gas fraction, and star formation rates are similar to those of nearby massive, star-forming galaxies, the quasar host galaxies possess exceptionally compact, disky molecular gas distributions with a median half-light radius of 1.8 kpc and molecular gas mass surface densities ≳22 M⊙ pc-2. While the overall velocity field of the molecular gas is dominated by regular rotation out to large radii, with ratio of rotation velocity to velocity dispersion ≳9, the nuclear region displays substantial kinematic complexity associated with small-scale substructure in the gas distribution. A tilted-ring analysis reveals that the kinematic and photometric position angles are misaligned on average by ∼ 34° ± 26° and provides evidence of kinematic twisting. These observations provide tantalizing clues to the detailed physical conditions of the circumnuclear environments of actively accreting supermassive black holes.

Keywords: agn host galaxies; galaxy kinematics; molecular gas; quasars; submillimeter astronomy
The Emission Properties of RRAT J0139+3336 at 1.25 GHz

Rotating Radio Transients are a relatively new subclass of pulsar characterized by sporadic bursting emission of single pulses. Here, we present a single-pulse analysis of a rotating radio transient, RRAT J0139+3336, using Five-hundred-meter Aperture Spherical radio Telescope at 1250 MHz. Within 3.32 hr of continuous observation, 152 single pulses were detected in RRAT J0139+3336, with the pulse rate of 45 pulses per hour. We perform a spectral analysis on the single pulses of this pulsar for the first time, finding its mean spectral indices to be -3.2 ± 0.2, which is steeper than most known pulsars. On a single-pulse basis, we produce the first polarimetric profile of this pulsar, which fits well with the rotating vector model. The single pulses are clearly affected by diffractive scintillation with a characteristic scintillation bandwidth of v sc = 28 ± 9 MHz. The pulse energy distribution for RRAT J0139+3336 can be described by a log-normal model.

Keywords: radio pulsars
The Drag Instability in a 2D Isothermal C-shock

We extend the linear analysis of the drag instability in a 1D perpendicular isothermal C-shock by Gu & Chen to 2D perpendicular and oblique C-shocks in the typical environment of star-forming clouds. Simplified dispersion relations are derived for the unstable modes. We find that the mode property of the drag instability generally depends on the ratio of the transverse (normal to the shock flow) to longitudinal (along the shock flow) wavenumber. For the transversely large-scale mode, the growth rate and wave frequency of the drag instability in a 2D shock resemble those in a 1D shock. For the transversely small-scale mode, the drag instability is characterized by an unstable mode coupled with an acoustic mode primarily along the transverse direction. When the shock is perpendicular or less oblique, there exists a slowly propagating mode, which can potentially grow into a nonlinear regime and contribute to the maximum growth of the instability. In contrast, when the shock is more oblique, this slowly propagating unstable mode disappears, and the maximum growth of the drag instability is likely contributed from the transversely large-scale mode (i.e., almost 1D mode). In all cases that we consider, the magnitude of the density perturbations is significantly larger than that of the velocity and magnetic field perturbations, implying that the density enhancement governs the dynamics in the linear regime of the instability. A few issues in the linear analysis, as well as the possible astrophysical implications, are also briefly discussed.

Keywords: shocks; plasma astrophysics; molecular clouds; interstellar magnetic fields
Comparison of Planetary Hα-emission Models: A New Correlation with Accretion Luminosity

Accreting planets have been detected through their hydrogen-line emission, specifically Hα. To interpret this, stellar-regime empirical correlations between the Hα luminosity LHα and the accretion luminosity Lacc or accretion rate $\dot{M}$ have been extrapolated to planetary masses, however without validation. We present a theoretical Lacc-LHα relationship applicable to a shock at the surface of a planet. We consider wide ranges of accretion rates and masses and use detailed spectrally resolved, nonequilibrium models of the postshock cooling. The new relationship gives a markedly higher Lacc for a given LHα than fits to young stellar objects, because Lyα, which is not observable, carries a large fraction of Lacc. Specifically, an LHα measurement needs 10 to 100 times higher Lacc and $\dot{M}$ than previously predicted, which may explain the rarity of planetary Hα detections. We also compare the $\dot{M}$ -LHα relationships coming from the planet-surface shock or implied by accretion-funnel emission. Both can contribute simultaneously to an observed Hα signal, but at low (high) $\dot{M}$ the planetary-surface shock (heated funnel) dominates. Only the shock produces Gaussian line wings. Finally, we discuss accretion contexts in which different emission scenarios may apply, putting recent literature models in perspective, and also present Lacc-Lline relationships for several other hydrogen lines.

Keywords: scaling relations; extrasolar gaseous giant planets; accretion; h i line emission; h alpha photometry; planet formation; classical t tauri stars
Mixed-mode Ensemble Asteroseismology of Low-luminosity Kepler Red Giants

We present measurements of the dipole mode asymptotic period spacing (ΔΠ1), the coupling factor between the p- and g-modes (q), the g-mode phase offset (ϵ g ), and the mixed-mode frequency rotational splitting (δ ν rot) for 1074 low-luminosity red giants from the Kepler mission. Using oscillation mode frequencies extracted from each star, we apply Bayesian optimization to estimate ΔΠ1 from the power spectrum of the stretched-period spectrum and to perform the subsequent forward modeling of the mixed-mode frequencies. With our measurements, we show that the mode coupling factor q shows significant anticorrelation with both the stellar mass and metallicity, and can reveal highly metal-poor stars. We present the evolution of ϵ g up the lower giant branch up to before the luminosity bump, and find no significant trends in ϵ g or δ ν rot with the stellar mass and metallicity in our sample. Additionally, we identify six new red giants showing anomalous distortions in their g-mode pattern. Our data products, code, and results are provided in a public repository.

Keywords: asteroseismology; stellar properties; stellar oscillations; astronomy data analysis
Stringent Tests of Gravity with Highly Relativistic Binary Pulsars in the Era of LISA and SKA

At present, 19 double neutron star (DNS) systems are detected by radio timing and two merging DNS systems are detected by kilohertz gravitational waves. Because of selection effects, none of them has an orbital period Pb in the range of a few tens of minutes. In this paper we consider a multimessenger strategy proposed by Kyutoku et al., jointly using the Laser Interferometer Space Antenna and the Square Kilometre Array to detect and study Galactic pulsar-neutron star (PSR-NS) systems with Pb ~ 10-100 minutes. We assume that we will detect PSR-NS systems by this strategy. We use standard pulsar-timing software to simulate times of arrival of pulse signals from these binary pulsars. We obtain the precision of timing parameters of short-orbital-period PSR-NS systems with orbital period Pb ∈ (8, 120) minutes. We use the simulated uncertainty of the orbital decay, ${\dot{P}}_{b}$ , to predict future tests for a variety of alternative theories of gravity. We show quantitatively that highly relativistic PSR-NS systems will significantly improve the constraint on parameters of specific gravity theories in the strong field regime. We also investigate the orbital periastron advance caused by the Lense-Thirring effect in a PSR-NS system with Pb = 8 minutes, and show that the Lense-Thirring effect will be detectable to a good precision.

Keywords: gravitation; binary pulsars; non-standard theories of gravity; pulsars; pulsar timing method
Constraining Galaxy Overdensities around Three z 6.5 Quasars with ALMA and MUSE

We quantify galaxy overdensities around three high-redshift quasars with known [C II]158 μm companions: PJ231-20 (z = 6.59), PJ308-21 (z = 6.24), and J0305-3150 (z = 6.61). Recent SCUBA2 imaging revealed the presence of 17 submillimeter galaxies (SMGs) with sky separations 0.'7 < θ < 2.'4 from these three quasars. We present ALMA Band 6 follow-up observations of these SCUBA2-selected SMGs to confirm their nature and redshift. We also search for continuum-undetected [C II]158 μm emitters in the ALMA pointings and make use of archival MUSE observations to search for Lyα emitters (LAEs) associated with the quasars. While most of the SCUBA2-selected sources are detected with ALMA in the continuum, no [C II]158 μm line emission could be detected, indicating that they are not at the quasar redshifts. Based on the serendipitous detection of CO 7-6 and [C I]809 μm emission lines, we find that four SMGs in the field of PJ231-20 are at z ~ 2.4, which is coincident with the redshift of an Mg II absorber in the quasar rest-frame UV spectrum. We report the discovery of two LAEs within <0.6 cMpc of PJ231-20 at the same redshift, indicating an LAE overdensity around this quasar. Taken together, these observations provide new constraints on the large-scale excess of Lyα- and [C II]158 μm-emitting galaxies around z > 6 quasars and suggest that only wide-field observations, such as MUSE, ALMA, or JWST mosaics, can reveal a comprehensive picture of large-scale structure around quasars in the first billion years of the universe.

Keywords: quasars; quasar-galaxy pairs; high-redshift galaxies; lyman-alpha galaxies; submillimeter astronomy