adsabs/SciX_UAT_keywords huggingface dataset:
The Formation of a 70 M⊙ Black Hole at High Metallicity

A 70 ${M}_{\odot }$ black hole (BH) was discovered in the Milky Way disk in a long-period detached binary system (LB-1) with a high-metallicity 8 ${M}_{\odot }$ B star companion. Current consensus on the formation of BHs from high-metallicity stars limits the BH mass to be below 20 ${M}_{\odot }$ due to strong mass loss in stellar winds. Using analytic evolutionary formulae, we show that the formation of a 70 ${M}_{\odot }$ BH in a high-metallicity environment is possible if wind mass-loss rates are reduced by factor of five. As observations indicate, a fraction of massive stars have surface magnetic fields that may quench the wind mass-loss, independently of stellar mass and metallicity. We confirm such a scenario with detailed stellar evolution models. A nonrotating 85 ${M}_{\odot }$ star model at Z = 0.014 with decreased winds ends up as a 71 ${M}_{\odot }$ star prior to core collapse with a 32 ${M}_{\odot }$ He core and a 28 ${M}_{\odot }$ CO core. Such a star avoids the pair-instability pulsation supernova mass loss that severely limits BH mass and may form a ∼70 ${M}_{\odot }$ BH in the direct collapse. Stars that can form 70 ${M}_{\odot }$ BHs at high Z expand to significant sizes, with radii of R ≳ 600 ${R}_{\odot }$ , however, exceeding the size of the LB-1 orbit. Therefore, we can explain the formation of BHs up to 70 ${M}_{\odot }$ at high metallicity and this result is valid whether or not LB-1 hosts a massive BH. However, if LB-1 hosts a massive BH we are unable to explain how such a binary star system could have formed without invoking some exotic scenarios.

Keywords: black hole physics; classical black holes; binary stars
Novel Approach to Forecasting Photospheric Emergence of Active Regions

One key aspect of understanding the solar dynamo mechanism and the evolution of solar magnetism is to properly describe the emergence of solar active regions. In this Letter, we describe the Lagrangian photospheric flows dynamics during a simulated flux emergence that produces an active region formed by pores. We analyze the lower photospheric flow organization prior, during and following the rise of an active region, uncovering the repelling and attracting photospheric structures that act as sources and sinks for magnetic element transport. Our results show that around 10 hr before the simulated emergence, considerable global changes are taking place on mesogranular scales indicated by an increase of the number of regions acting as a source to the multiple and scattered emergences of small-scale magnetic flux. At the location of active region's appearance, the converging flows become weaker and there is an arising of a diverging region 8 hr before the emergence time. Our study also indicates that the strong concentration of magnetic field affects the flow dynamics beyond the area of the actual simulated pores, leading to complex and strongly diverging flows in the neighboring regions. Our findings suggest that the Lagrangian analysis is a powerful tool to describe the changes in the photospheric flows due to magnetic flux emergence.

Keywords: solar magnetic flux emergence; solar active region velocity fields; solar convective zone
A Blueprint for the Milky Way's Stellar Populations. III. Spatial Distributions and Population Fractions of Local Halo Stars

We analyze the observed spatial, chemical and dynamical distributions of local metal-poor stars, based on photometrically derived metallicity and distance estimates along with proper motions from the Gaia mission. Along the Galactic prime meridian, we identify stellar populations with distinct properties in the metallicity versus rotational velocity space, including Gaia Sausage/Enceladus (GSE), the metal-weak thick disk (MWTD), and the Splash (sometimes referred to as the "in situ" halo). We model the observed phase-space distributions using Gaussian mixtures and refine their positions and fractional contributions as a function of distances from the Galactic plane ( $| Z| $ ) and the Galactic center ( ${R}_{\mathrm{GC}}$ ), providing a global perspective of the major stellar populations in the local halo. Within the sample volume ( $| Z| \lt 6\,\mathrm{kpc}$ ), stars associated with GSE exhibit a larger proportion of metal-poor stars at greater ${R}_{\mathrm{GC}}$ ( ${\rm{\Delta }}\langle [\mathrm{Fe}/{\rm{H}}]\rangle /{\rm{\Delta }}{R}_{\mathrm{GC}}=-0.05\pm 0.02\,\mathrm{dex}\,{\mathrm{kpc}}^{-1}$ ). This observed trend, along with a mild anticorrelation of the mean rotational velocity with metallicity ( ${\rm{\Delta }}\langle {v}_{\phi }\rangle /{\rm{\Delta }}\langle [\mathrm{Fe}/{\rm{H}}]\rangle \sim -10\ \mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{dex}}^{-1}$ ), implies that more metal-rich stars in the inner region of the GSE progenitor were gradually stripped away, while the prograde orbit of the merger at infall became radialized by dynamical friction. The metal-rich GSE stars are causally disconnected from the Splash structure, whose stars are mostly found on prograde orbits (≳94%) and exhibit a more centrally concentrated distribution than GSE. The MWTD exhibits a similar spatial distribution to the Splash, suggesting earlier dynamical heating of stars in the primordial disk of the Milky Way, possibly before the GSE merger.

Keywords: milky way galaxy; milky way stellar halo; milky way dynamics; milky way formation; milky way evolution; stellar abundances; stellar populations
Detection of the Hg II Line at 3983.93 Å in One Optical Spectrum of Maia

Evidence is reported for the first time for the presence of the Hg II line in a Narval I profile of Maia, the fourth brightest member of the Pleiades open cluster. The Hg II line in Maia absorbs about 2% of the local continuum and can be reproduced with an overabundance of mercury of about 4000 times the solar mercury abundance. This line is probably variable suggesting that mercury might be distributed in spot(s) over the surface of Maia. Maia is currently classified as a He-weak Mn star, it should probably be reclassified as a HgMn star.

Keywords: chemically peculiar stars; mercury-manganese stars
Spectral Shapes of the Lyα Emission from Galaxies. I. Blueshifted Emission and Intrinsic Invariance with Redshift

We demonstrate the redshift evolution of the spectral profile of H I Lyα emission from star-forming galaxies. In this first study we pay special attention to the contribution of blueshifted emission. At redshift z = 2.9-6.6, we compile spectra of a sample of 229 Lyα-selected galaxies identified with the Multi-Unit Spectroscopic Explorer at the Very Large Telescope, while at low z ( < 0.44) we use a sample of 74 ultraviolet-selected galaxies observed with the Cosmic Origin Spectrograph on board the Hubble Space Telescope. At low z, where absorption from the intergalactic medium (IGM) is negligible, we show that the ratio of Lyα luminosity blueward and redward of line center (LB/R) increases rapidly with increasing equivalent width (WLyα). This correlation does not, however, emerge at z = 3-4, and we use bootstrap simulations to demonstrate that trends in LB/R should be suppressed by variations in IGM absorption. Our main result is that the observed blueshifted contribution evolves rapidly downward with increasing redshift: LB/R ≈ 30% at z ≈ 0, but dropping to 15% at z ≈ 3, and to below 3% by z ≈ 6. Applying further simulations of the IGM absorption to the unabsorbed COS spectrum, we demonstrate that this decrease in the blue-wing contribution can be entirely attributed to the thickening of intervening Lyα absorbing systems, with no need for additional H I opacity from local structure, companion galaxies, or cosmic infall. We discuss our results in light of the numerical radiative transfer simulations, the evolving total Lyα and ionizing output of galaxies, and the utility of resolved Lyα spectra in the reionization epoch. * Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

Keywords: radiative transfer; lyman-alpha galaxies; galaxy evolution; high-redshift galaxies; h i line emission; intergalactic medium; starburst galaxies
Recoverability of Known Near-Earth Asteroids

This paper analyzes the current population of known near-Earth asteroids (NEAs) and presents statistics on the recoverability of NEAs with both targeted observation campaigns and all-sky surveys. For an asteroid to be observable at a future apparition, given the right geometry, the plane-of-sky uncertainty must be small enough to be covered by a telescope's field of view and the asteroid must be brighter than the detector's limiting magnitude. Since recoverability is a telescope-dependent property, we select two representative instruments that span a wide range of capability and availability: the 1.0 m I52 telescope of the Catalina Sky Survey and the Hyper Suprime-Cam of the 8.2 m Subaru telescope. Based on this choice, we classify asteroids as recoverable, potentially recoverable, and not recoverable depending on whether they could be detected with an I52-class telescope, only with a Subaru-class telescope, or with neither, respectively. Using these definitions, we find that the majority (90%) of NEAs with H < 22 and most (93%) potentially hazardous asteroids are recoverable or potentially recoverable in the next 50 yr. When considering fainter asteroids down to H ≤ 28, about two-thirds of the NEA population and half of the low minimum-orbit intersection distance (MOID) asteroids (MOID ≤ 0.05 au) are either recoverable or potentially recoverable. As of 2019 October 13, the Sentry risk list includes 193 objects with an impact probability greater than 10-6 that are not recoverable. The fraction of NEAs and low-MOID NEAs that are not recoverable can be reduced by up to 47% and 43%, respectively, when incorporating statistical estimates of serendipitous recoveries by all-sky surveys.

Keywords: near-earth objects; sky surveys; solar system astronomy; asteroids
On the Dynamical Heating of Dwarf Galaxies in a Fuzzy Dark Matter Halo

Fuzzy dark matter (FDM), consisting of ultralight bosons, is an intriguing alternative to cold dark matter. Numerical simulations solving the Schrödinger-Poisson (SP) equation, which governs FDM dynamics, show that FDM halos consist of a central solitonic core (representing the ground state of the SP equation), surrounded by a large envelope of excited states. Wave interference gives rise to density fluctuations of order unity throughout the envelope and causes the soliton to undergo density oscillations and execute a confined random walk in the central region of the halo. The resulting gravitational potential perturbations are an efficient source of dynamical heating. Using high-resolution numerical simulations of a 6.6 × 109 M ⊙ FDM halo with boson mass m b = 8 × 10-23 eV, we investigate the impact of this dynamical heating on the structure and kinematics of spheroidal dwarf galaxies of a fixed mass but different initial sizes and ellipticities. The galaxies are set up in equilibrium in the time-and-azimuthally averaged halo potential and evolved for 10 Gyr in the live FDM halo. We find that they continuously increase their sizes and central velocity dispersions. In addition, their kinematic structures become strongly radially anisotropic, especially in the outskirts. Dynamical heating also causes initially ellipsoidal galaxies to become more spherical over time from the inside out and gives rise to distorted, nonconcentric isodensity contours. These telltale characteristics of dynamical heating of dwarf galaxies in FDM halos can potentially be used to constrain the boson mass.

Keywords: galaxy dynamics; galaxy dark matter halos; gravitational interaction
Gaia EDR3 Reveals the Substructure and Complicated Star Formation History of the Greater Taurus-Auriga Star-forming Complex

The Taurus-Auriga complex is the prototypical low-mass star-forming region, and provides a unique testbed of the star formation process, which left observable imprints on the spatial, kinematic, and temporal structure of its stellar population. Taurus's rich observational history has uncovered peculiarities that suggest a complicated star-forming event, such as members at large distances from the molecular clouds and evidence of an age spread. With Gaia, an in-depth study of the Taurus census is possible, to confirm membership, identify substructure, and reconstruct its star formation history. We have compiled an expansive census of the greater Taurus region, identifying spatial subgroups and confirming that Taurus is substructured across stellar density. There are two populations of subgroups: clustered groups near the clouds and sparse groups spread throughout the region. The sparse groups comprise Taurus's distributed population, which is on average older than the population near the clouds, and hosts subpopulations up to 15 Myr old. The ages of the clustered groups increase with distance, suggesting that the current star formation was triggered from behind. Still, the region is kinematically coherent, and its velocity structure reflects an initial turbulent spectrum similar to Larson's Law that has been modified by dynamical relaxation. Overall, Taurus has a complicated star formation history, with at least two epochs of star formation featuring both clustered and distributed modes. Given the correlations between age and spatial distribution, Taurus might be part of a galaxy-scale star-forming event that can only begin to be understood in the Gaia era.

Keywords: star formation
Super-Eddington Magnetized Neutron Star Accretion Flows: A Self-similar Analysis

The properties of super-Eddington accretion disks exhibit substantial distinctions from the sub-Eddington ones. In this paper, we investigate the accretion process of a magnetized neutron star (NS) surrounded by a super-Eddington disk. By constructing self-similar solutions for the disk structure, we study in detail an interaction between the NS magnetosphere and the inner region of the disk, revealing that this interaction takes place within a thin boundary layer. The magnetosphere truncation radius is found to be approximately proportional to the Alfvén radius, with a coefficient ranging between 0.34–0.71, influenced by the advection and twisting of a magnetic field, NS rotation, and radiation emitted from an NS accretion column. Under super-Eddington accretion, the NS can readily spin up to become a rapid rotator. The proposed model can be employed to explore the accretion and evolution of NSs in diverse astrophysical contexts, such as ultraluminous X-ray binaries or active galactic nucleus disks.

Keywords: compact objects; neutron stars; accretion
Neutral Atomic and Molecular Clouds and Star Formation in the Outer Carina Arm

We present a comprehensive investigation of H I (super)clouds, molecular clouds (MCs), and star formation in the Carina spiral arm of the outer Galaxy. Utilizing HI4PI and CfA CO survey data, we identify H I clouds and MCs based on the (l, v LSR) locations of the Carina arm. We analyzed 26 H I clouds and 48 MCs. Most of the identified H I clouds are superclouds, with masses exceeding 106 M ⊙. We find that 15 of these superclouds have associated MC(s) with M H I ≳ 106 M ⊙ and ${{\rm{\Sigma }}}_{{\rm{H}}\,{\rm\small{I}}+{{\rm{H}}}_{2}}\gtrsim $ 50 M ⊙ pc-2. Our virial equilibrium analysis suggests that these CO-bright H I clouds are gravitationally bound or marginally bound. We report an anticorrelation between molecular mass fractions and Galactocentric distances, and a correlation with total gas surface densities. Nine CO-bright H I superclouds are associated with H II regions, indicating ongoing star formation. We confirm the regular spacing of H I superclouds along the spiral arm, which is likely due to some underlying physical process, such as gravitational instabilities. We observe a strong spatial correlation between H II regions and MCs, with some offsets between MCs and local H I column density peaks. Our study reveals that, in the context of H I superclouds, the star formation rate surface density is independent of H I and total gas surface densities but positively correlates with molecular gas surface density. This finding is consistent with both extragalactic studies of the resolved Kennicutt-Schmidt relation and local giant molecular clouds study of Lada et al. (2013), emphasizing the crucial role of molecular gas in regulating star formation processes.

Keywords: interstellar clouds
Magnetospheric Multiscale Observations of Foreshock Transients at Their Very Early Stage

Foreshock transients are ion kinetic structures in the ion foreshock. Due to their dynamic pressure perturbations, they can disturb the bow shock and magnetosphere-ionosphere system. They can also accelerate particles contributing to shock acceleration. However, it is still unclear how exactly they form. Recent particle-in-cell simulations point out the important role of the electric field and Hall current in the formation process. To further examine this, we use data from the Magnetospheric Multiscale (MMS) mission to apply case studies on two small (1000-2000 km) foreshock transient events that just started to form. In event 1 where MMS was in a tetrahedral formation, we show that the current density configuration, which determined the magnetic field profile, was mainly driven by Hall currents generated by demagnetized foreshock ions. The resulting time variation of the magnetic field induced an electric field that drove cold plasma moving outward with magnetic field lines. In event 2 where MMS was in a string-of-pearls formation, we analyze the evolution of field and plasma parameters. We show that the magnetic flux and mass flux were transported outward from the core, resulting in the steepening of the boundary. The steepened boundary, which trapped more foreshock ions and caused stronger demagnetization of foreshock ions, nonlinearly further enhanced the Hall current. Based on our observations, we propose a physical formation process wherein the positive feedback of foreshock ions on the varying magnetic field caused by the foreshock ion Hall current enables an "instability" and the growth of the structure.

Keywords: planetary bow shocks; shocks
A Joint Microwave and Hard X-Ray Study toward Understanding the Transport of Accelerated Electrons During an Eruptive Solar Flare

The standard flare model, despite its success, is limited in comprehensively explaining the various processes involving nonthermal particles. One such missing ingredient is a detailed understanding of the various processes involved during the transport of accelerated electrons from their site of acceleration to different parts of the flare region. Here we use simultaneous radio and X-ray observations from the Expanded Owens Valley Solar Array and the Spectrometer/Telescope for Imaging X-rays on board the Solar Orbiter, respectively, from two distinct viewing perspectives, to study the electron transport processes. Through detailed spectral modeling of the coronal source using radio data and footpoint sources using X-ray spectra, we compare the nonthermal electron distribution at the coronal and footpoint sources. We find that the flux of the nonthermal electrons precipitated at the footpoint is an order of magnitude greater than that trapped in the looptop, consistent with earlier works that primarily used X-ray for their studies. In addition, we find that the electron spectral indices obtained from X-ray footpoints are significantly softer than the spectral hardness of the nonthermal electron distribution in the corona. We interpret these differences based on transport effects and the difference in sensitivity of microwave and X-ray observations to different regimes of electron energies. Such an understanding is crucial for leveraging different diagnostic methods of nonthermal electrons simultaneously to achieve a more comprehensive understanding of the electron acceleration and transport processes of solar flares.

Keywords: solar flares; solar radio flares; solar x-ray flares
Magnetic Discontinuities in the Solar Wind and Magnetosheath: Magnetospheric Multiscale Mission (MMS) Observations

We perform a statistical investigation of the geometric features of interplanetary discontinuities (IDs) in the near-Earth solar wind and magnetosheath, by utilizing 14 months of Magnetospheric Multiscale mission data. 117,669 IDs are collected, including 108,049 events in the solar wind and 6399 events in the magnetosheath, with the remnant in the magnetosphere or near the bow shock/magnetopause. We find the following: (1) the ID occurrence rate is 17.0 events hr-1 in the solar wind and 5.5 events hr-1 in the magnetosheath, (2) the field rotation angles during ID crossings in the magnetosheath exhibit a two-exponential distribution with a breakpoint at 50°, which is not observed for IDs in the solar wind, (3) the magnetosheath IDs with small field rotation angles tend to be clustered, (4) by classifying the IDs into rotational discontinuities (RDs), tangential discontinuities (TDs), either TDs or RDs (EDs), and neither TDs nor RDs (NDs), we estimate RD:TD:ED:ND = 68%:5%:20%:7% in the solar wind, and RD:TD:ED:ND = 15%:44%:18%:23% in the magnetosheath, (5) the occurrence rates of RDs and TDs are, respectively 7.95 and 0.58 events hr-1 in the solar wind, and 0.57 and 1.60 events hr-1 in the magnetosheath, (6) RDs are more likely to propagate antisunward in the plasma rest frame, especially in the magnetosheath, and (7) the average thicknesses of the RDs and TDs are estimated, respectively, as 10.4 and 8.1 proton gyroradii (r p ) in the solar wind, and 17.4 and 5.0 r p in the magnetosheath. This work can improve our understanding of IDs' interaction with the terrestrial bow shock.

Keywords: interplanetary discontinuities; solar wind; interplanetary magnetic fields; magnetohydrodynamics
Categorization of Spatial and Temporal Ejecta Outcomes in Binary Systems Based on Variations of the Didymos System

With the increasing number of binary asteroid systems being discovered, ejecta studies must expand from solely investigating single-body systems to modeling more complex multiple-body systems. For example, the Double Asteroid Redirection Test provides an opportunity to study the dynamics of a debris cloud around Didymos and Dimorphos, a near-Earth binary asteroid system. Here we simulate 72 variations on the Didymos system in order to categorize types of ejecta outcomes and analyze the influence of the varying system parameters on each outcome. We have varied five parameters: the system separation, the mass ratio between the two bodies, the impact location, the target-body shape, and the target-body rotation period. The resulting provenance maps of the final ejecta distributions were blindly sorted into five categories, while the resulting cumulative distribution functions (CDFs), describing the rate at which particles hit the surface, were blindly sorted into eight categories. We count the occurrences of the parameter values in each of the categories and apply a Cramer's V statistical test to evaluate the significance of the association between each varied effect and the overall grouping of the provenance maps and CDFs. We conclude that more dominant effects, such as a small rotation period, produce notably similar ejecta distributions that result in being assigned to the same category. Less dominant effects, such as target-body location, are sorted into several categories due to the larger influence of varying dominant effects.

Keywords: asteroid satellites; ejecta; surface processes; asteroid surfaces; impact phenomena; n-body simulations; asteroid dynamics