adsabs/SciX_UAT_keywords huggingface dataset:
The X-Ray Coronae in NuSTAR Bright Active Galactic Nuclei

We present a systematic and uniform analysis of NuSTAR data of a sample of 60 SWIFT BAT-selected AGNs with 10-78 keV signal-to-noise ratio (S/N) > 50, 10 of which are radio loud. We measure their high-energy cutoff E cut or coronal temperature T e using three different spectral models to fit their NuSTAR spectra and show that a threshold in NuSTAR spectral S/N is essential for such measurements. High-energy spectral breaks are detected in the majority of the sample, and for the rest, strong constraints on E cut or T e are obtained. Strikingly, we find extraordinarily large E cut lower limits (>400 keV, up to >800 keV) in 10 radio-quiet sources, whereas we find none in the radio-loud sample. Consequently and surprisingly, we find a significantly larger mean E cut/T e of radio-quiet sources compared with radio-loud ones. The reliability of these measurements is carefully inspected and verified with simulations. We find a strong positive correlation between E cut and photon index Γ, which cannot be attributed to the parameter degeneracy. The strong dependence of E cut on Γ, which could fully account for the discrepancy of the E cut distribution between radio-loud and radio-quiet sources, indicates that the X-ray coronae in AGNs with steeper hard X-ray spectra have on average higher temperature and thus smaller opacity. However, no prominent correlation is found between E cut and λ edd. In the l-Θ diagram, we find a considerable fraction of sources lie beyond the boundaries of forbidden regions due to runaway pair production, posing (stronger) challenges to various (flat) coronal geometries.

Keywords: active galactic nuclei; x-ray active galactic nuclei
Unusually Low-frequency Whistler-mode Waves and Their Association with High-energy Protons Observed Upstream of Martian Bow Shock

Whistler-mode waves upstream of planetary bow shock are often referred to as "1-Hz waves" due to the center of their observed frequency range being at ∼1 Hz. A series of whistler-mode waves were observed upstream of the Martian bow shock by MAVEN on 2015 August 14, with unusually low frequencies centered at ∼0.4 Hz. These waves were accompanied (though not synchronized) by the significant flux enhancement of high-energy protons up to ∼10 keV. By analyzing the wave dispersion property and the wave–particle interaction condition, we find that the observed whistler-mode waves have the potential of resonating with protons of ∼1 keV with large pitch angles up to nearly perpendicular to the background magnetic field, thereby providing a feasible means of accounting for proton acceleration. Our results indicate the possible origin of energized protons in the Martian environment through the interaction with whistler-mode waves, and their potential relationship with the unique upstream conditions.

Keywords: mars; solar wind; plasma physics
Hydration of Nebular Minerals through the Implantation-Diffusion Process

Recent studies have detected structurally bound water in the refractory silicate minerals present in ordinary and enstatite chondrite meteorites. The mechanism for the incorporation of the hydrogen is not well defined. In this paper we quantitatively examine a two-fold process involving the implantation and diffusion of nebular hydrogen ions that is responsible for the hydration of the chondritic minerals. Our simulations show that depending on critical parameters, including the flux of the protons in nebular plasma, retention coefficient, temperature of the silicate minerals, and desorption rate of implanted hydrogen, the implantation of low-energy hydrogen ions can result in equivalent water contents of ∼0.1 wt% in chondritic silicates within 10 years. Thus, this novel mechanism operating in the nebula at 10-3 bar pressure and <650 K temperatures can efficiently hydrate the free-floating chondritic minerals prior to the rapid formation of planetesimals inside the snow line, and agree well with the wet accretion scenario for the inner solar system objects.

Keywords: solar system planets; chondrules; silicate grains
DRAGONS-A Quick Overview

Data Reduction for Astronomy from Gemini Observatory North and South (DRAGONS) is a platform for the reduction and processing of astronomical data. The Python-based, open-source package includes infrastructure for automation and algorithms for the processing of imaging and spectroscopic data, up to the analysis-ready stage. DRAGONS currently focuses on the reduction of Gemini data, although it allows for support of data from other instruments and telescopes through third-party extensions. Its latest release (v3.1) enables automated reduction of all currently active Gemini imaging facility instruments, as well as optical longslit spectroscopic data, acquired with GMOS.

Keywords: astronomy software; astronomy data reduction
Target Selection and Sample Characterization for the DESI LOW-Z Secondary Target Program

We introduce the DESI LOW-Z Secondary Target Survey, which combines the wide-area capabilities of the Dark Energy Spectroscopic Instrument (DESI) with an efficient, low-redshift target selection method. Our selection consists of a set of color and surface brightness cuts, combined with modern machine-learning methods, to target low-redshift dwarf galaxies (z < 0.03) between 19 < r < 21 with high completeness. We employ a convolutional neural network (CNN) to select high-priority targets. The LOW-Z survey has already obtained over 22,000 redshifts of dwarf galaxies (M * < 109 M ⊙), comparable to the number of dwarf galaxies discovered in the Sloan Digital Sky Survey DR8 and GAMA. As a spare fiber survey, LOW-Z currently receives fiber allocation for just ~50% of its targets. However, we estimate that our selection is highly complete: for galaxies at z < 0.03 within our magnitude limits, we achieve better than 95% completeness with ~1% efficiency using catalog-level photometric cuts. We also demonstrate that our CNN selections z < 0.03 galaxies from the photometric cuts subsample at least 10 times more efficiently while maintaining high completeness. The full 5 yr DESI program will expand the LOW-Z sample, densely mapping the low-redshift Universe, providing an unprecedented sample of dwarf galaxies, and providing critical information about how to pursue effective and efficient low-redshift surveys.

Keywords: redshift surveys; computational methods; dwarf galaxies; low surface brightness galaxies
Exploring the Stellar Age Distribution of the Milky Way Bulge Using APOGEE

We present stellar age distributions of the Milky Way bulge region using ages for ∼6000 high-luminosity ( $\mathrm{log}(g)\lt 2.0$ ), metal-rich ([Fe/H] ≥ -0.5) bulge stars observed by the Apache Point Observatory Galactic Evolution Experiment. Ages are derived using The Cannon label-transfer method, trained on a sample of nearby luminous giants with precise parallaxes for which we obtain ages using a Bayesian isochrone-matching technique. We find that the metal-rich bulge is predominantly composed of old stars (>8 Gyr). We find evidence that the planar region of the bulge ( $| {Z}_{\mathrm{GC}}| \leqslant 0.25$ kpc) is enriched in metallicity, Z, at a faster rate (dZ/dt ∼ 0.0034 Gyr-1) than regions farther from the plane (dZ/dt ∼ 0.0013 Gyr-1 at $| {Z}_{\mathrm{GC}}| \gt 1.00$ kpc). We identify a nonnegligible fraction of younger stars (age ∼2-5 Gyr) at metallicities of +0.2 < [Fe/H] < +0.4. These stars are preferentially found in the plane ( $| {Z}_{\mathrm{GC}}| \leqslant 0.25$ kpc) and at Rcy ≈ 2-3 kpc, with kinematics that are more consistent with rotation than are the kinematics of older stars at the same metallicities. We do not measure a significant age difference between stars found inside and outside the bar. These findings show that the bulge experienced an initial starburst that was more intense close to the plane than far from the plane. Then, star formation continued at supersolar metallicities in a thin disk at 2 kpc ≲ Rcy ≲ 3 kpc until ∼2 Gyr ago.

Keywords: galactic bulge; milky way galaxy; milky way evolution; milky way formation; stellar ages; galaxy bulges
Cosmic Evolution of the H2 Mass Density and the Epoch of Molecular Gas

We present new empirical constraints on the evolution of ${\rho }_{{{\rm{H}}}_{2}}$ , the cosmological mass density of molecular hydrogen, back to z ≈ 2.5. We employ a statistical approach measuring the average observed 850 μm flux density of near-infrared selected galaxies as a function of redshift. The redshift range considered corresponds to a span where the 850 μm band probes the Rayleigh-Jeans tail of thermal dust emission in the rest frame, and can therefore be used as an estimate of the mass of the interstellar medium. Our sample comprises of ≈150,000 galaxies in the UK InfraRed Telescope Infrared Deep Sky Survey Ultra-Deep Survey field with near-infrared magnitudes KAB ≤ 25 mag and photometric redshifts with corresponding probability distribution functions derived from deep 12-band photometry. With a sample approximately 2 orders of magnitude larger than in previous works we significantly reduce statistical uncertainties on ${\rho }_{{{\rm{H}}}_{2}}$ to z ≈ 2.5. Our measurements are in broad agreement with recent direct estimates from blank field molecular gas surveys, finding that the epoch of molecular gas coincides with the peak epoch of star formation with ${\rho }_{{{\rm{H}}}_{2}}\approx 2\times {10}^{7}\,{M}_{\odot }\,{\mathrm{Mpc}}^{-3}$ at z ≈ 2. We demonstrate that ${\rho }_{{{\rm{H}}}_{2}}$ can be broadly modeled by inverting the star formation rate (SFR) density with a fixed or weakly evolving star formation efficiency. This "constant efficiency" model shows a similar evolution to our statistically derived ${\rho }_{{{\rm{H}}}_{2}}$ , indicating that the dominant factor driving the peak star formation history at z ≈ 2 is a larger supply of molecular gas in galaxies rather than a significant evolution of the SFR efficiency within individual galaxies.

Keywords: galaxy evolution; high-redshift galaxies; interstellar medium; star formation
The Long Stare at Hercules X-1. I. Emission Lines from the Outer Disk, the Magnetosphere Boundary, and the Accretion Curtain

Hercules X-1 is a nearly edge-on accreting X-ray pulsar with a warped accretion disk, precessing with a period of about 35 days. The disk precession allows for unique and changing sightlines toward the X-ray source. To investigate the accretion flow at a variety of sightlines, we obtained a large observational campaign on Her X-1 with XMM-Newton (380 ks exposure) and Chandra (50 ks exposure) for a significant fraction of a single disk precession cycle, resulting in one of the best data sets taken to date on a neutron star X-ray binary. Here we present the spectral analysis of the high state high-resolution grating and CCD data sets, including the extensive archival data available for this famous system. The observations reveal a complex Fe K region structure, with three emission line components of different velocity widths. Similarly, the high-resolution soft X-ray spectra reveal a number of emission lines of various widths. We correct for the uncertain gain of the European Photon Imaging Camera pn Timing mode spectra, and track the evolution of these spectral components with Her X-1 precession phase and observed luminosity. We find evidence for three groups of emission lines, the first of which originates in the outer accretion disk (105 R G from the neutron star). The second line group plausibly originates at the boundary between the inner disk and the pulsar magnetosphere (103 R G). The last group is too broad to arise in the magnetically truncated disk and instead must originate very close to the neutron star surface, likely from X-ray reflection from the accretion curtain (~102 R G).

Keywords: accretion; neutron stars; x-ray binary stars
An 8.8 Minute Orbital Period Eclipsing Detached Double White Dwarf Binary

We report the discovery of ZTF J2243+5242, an eclipsing double white dwarf binary with an orbital period of just 8.8 minutes, the second known eclipsing binary with an orbital period of less than 10 minutes. The system likely consists of two low-mass white dwarfs and will merge in approximately 400,000 yr to form either an isolated hot subdwarf or an R Coronae Borealis star. Like its 6.91 minute counterpart, ZTF J1539+5027, ZTF J2243+5242 will be among the strongest gravitational-wave sources detectable by the space-based gravitational-wave detector the Laser Space Interferometer Antenna (LISA) because its gravitational-wave frequency falls near the peak of LISA's sensitivity. Based on its estimated distance of $d={2425}_{-114}^{+108}\,\mathrm{pc}$ , LISA should detect the source within its first few months of operation and achieve a signal-to-noise ratio of 63 ± 7 after 4 yr. We find component masses of ${M}_{A}={0.323}_{-0.047}^{+0.065}$ and ${M}_{B}={0.335}_{-0.054}^{+0.052}\,{M}_{\odot }$ , radii of ${R}_{A}={0.0298}_{-0.0012}^{+0.0013}$ and ${R}_{B}={0.0275}_{-0.0013}^{+0.0012}\,{R}_{\odot }$ , and effective temperatures of ${T}_{A}={26,300}_{-900}^{+1700}$ and ${T}_{B}={19,200}_{-900}^{+1500}\,{\rm{K}}$ . We determine all of these properties and the distance to this system using only photometric measurements, demonstrating a feasible way to estimate parameters for the large population of optically faint (r > 21 mAB) gravitational-wave sources that the Vera Rubin Observatory and LISA should identify.

Keywords: white dwarf stars; gravitational wave sources; compact binary stars
Enhanced Oxygen Ion Outflow at Earth and Mars due to the Concurrent Impact of a Stream Interaction Region

One of the major processes that solar wind drives is the outflow and escape of ions from the planetary atmospheres. The major ion species in the upper ionospheres of both Earth and Mars is O+, and hence it is more likely to dominate the escape process. On Earth, due to a strong intrinsic magnetic field, the major ion outflow pathways are through the cusp, polar cap, and the auroral oval. In contrast, Mars has an induced magnetosphere, where the ionosphere is in direct contact with the shocked solar wind plasma. Therefore, physical processes underlying the ion energization and escape rates are expected to be different on Mars as compared to Earth. In the current work, we study the near-simultaneous ion outflow event from both Earth and Mars during the passage of a stream interaction region/high-speed stream (SIR/HSS) during 2016 May, when both the planets were approximately aligned on the same side of the Sun. The SIR/HSS propagation was recorded by spacecraft at the Sun–Earth L1 point and Mars Express at 1.5 au. During the passage of the SIR, the dayside and nightside ion outflows at Earth were observed by Van Allen Probes and Magnetospheric Multiscale Mission orbiters, respectively. At Mars, the ion energization at different altitudes was observed by the STATIC instrument on board the MAVEN orbiter. We observe evidence for the enhanced ion outflow from both Earth and Mars during the passage of the SIR, and identify the dominant drivers of the ion outflow.

Keywords: space weather; fast solar wind; planetary magnetospheres
The Reservoir of the Per-emb-2 Streamer

Streamers bring gas from outer regions to protostellar systems and could change the chemical composition around protostars and protoplanetary disks. We have carried out mapping observations of carbon-chain species (HC3N, HC5N, CCH, and CCS) in the 3 mm and 7 mm bands toward the streamer flowing to the Class 0 young stellar object (YSO) Per-emb-2 with the Nobeyama 45 m radio telescope. A region with a diameter of ∼0.04 pc is located to the north at a distance of ∼20,500 au from the YSO. The streamer connects to this northern region, which is its origin. The reservoir has high density and low temperature ( ${n}_{{{\rm{H}}}_{2}}\approx 1.9\times {10}^{4}$ cm‑3, T kin = 10 K), which are similar to those of early-stage starless cores. By comparison of the observed abundance ratios of CCS/HC3N to the chemical simulations, the reservoir and streamer are found to be chemically young. The total mass available for the streamer is derived to be 24–34 M ⊙. It has been estimated that, if all of the gas in the reservoir were to accrete onto the Per-emb-2 protostellar system, the lifetime of the streamer would be (1.1–3.2) × 105 yr, suggesting that the mass accretion via the streamer would continue until the end of the Class I stage.

Keywords: astrochemistry; low mass stars; star formation; young stellar objects
Discovery of a Highly Neutronized Ejecta Clump in the Type Ia Supernova Remnant 3C 397

The supernova remnant (SNR) 3C 397 is thought to originate from a Type Ia supernova (SN Ia) explosion of a near-Chandrasekhar-mass (MCh) progenitor, based on the enhanced abundances of Mn and Ni revealed by previous X-ray study with Suzaku. Here we report follow-up XMM-Newton observations of this SNR, conducted with the aim of investigating the detailed spatial distribution of the Fe-peak elements. We have discovered an ejecta clump with extremely high abundances of Ti and Cr, in addition to Mn, Fe, and Ni, in the southern part of the SNR. The Fe mass of this ejecta clump is estimated to be ∼0.06 M⊙, under the assumption of a typical Fe yield for SNe Ia (i.e., ∼0.8 M⊙). The observed mass ratios among the Fe-peak elements and Ti require substantial neutronization that is achieved only in the innermost regions of a near-MCh SN Ia with a central density of ρc ∼ 5 × 109 g cm-3, significantly higher than typically assumed for standard near-MCh SNe Ia (ρc ∼ 2 × 109 g cm-3). The overproduction of the neutron-rich isotopes (e.g., 50Ti and 54Cr) is significant in such high-ρc SNe Ia, with respect to the solar composition. Therefore, if 3C 397 is a typical high-ρc near-MCh SN Ia remnant, the solar abundances of these isotopes could be reproduced by the mixture of the high- and low-ρc near-MCh and sub-MCh Type Ia events, with ≲20% being high-ρc near-MCh.

Keywords: supernova remnants
Elemental Abundances of Major Elements in the Solar Wind as Measured in Genesis Targets and Implications on Solar Wind Fractionation

We present elemental abundance data of C, N, O, Na, Mg, Al, Ca, and Cr in Genesis silicon targets. For Na, Mg, Al, and Ca, data from three different solar wind (SW) regimes are also presented. Data were obtained by backside depth profiling using secondary ion mass spectrometry. The accuracy of these measurements exceeds those obtained by in situ observations; therefore, the Genesis data provide new insights into elemental fractionation between Sun and SW, including differences between SW regimes. We integrate previously published noble gas and hydrogen elemental abundances from Genesis targets, as well as preliminary values for K and Fe. The abundances of the SW elements measured display the well-known fractionation pattern that correlates with each element's first-ionization potential (FIP). When normalized either to spectroscopic photospheric solar abundances or to those derived from CI-chondritic meteorites, the fractionation factors of low-FIP elements (K, Na, Al, Ca, Cr, Mg, Fe) are essentially identical within uncertainties, but the data are equally consistent with increasing fractionation with decreasing FIP. The elements with higher FIPs between ∼11 and ∼16 eV (C, N, O, H, Ar, Kr, Xe) display a relatively well-defined trend of increasing fractionation with decreasing FIP, if normalized to modern 3D photospheric model abundances. Among the three Genesis regimes, the fast SW displays the least elemental fractionation for almost all elements (including the noble gases) but differences are modest: for low-FIP elements, the precisely measured fast-slow SW variations are less than 3%.

Keywords: solar wind; solar abundances; fast solar wind; slow solar wind; solar coronal mass ejections; chemical abundances
Retrieving Exoplanet Atmospheres Using Planetary Infrared Excess: Prospects for the Night Side of WASP-43 b and Other Hot Jupiters

To increase the sample size of future atmospheric characterization efforts, we build on the planetary infrared excess (PIE) technique that has been proposed as a means to detect and characterize the thermal spectra of transiting and non-transiting exoplanets using sufficiently broad wavelength coverage to uniquely constrain the stellar and planetary spectral components from spatially unresolved observations. We performed simultaneous retrievals of stellar and planetary spectra for the archetypal planet WASP-43b in its original configuration and a non-transiting configuration to determine the efficacy of the PIE technique for characterizing the planet's night-side atmospheric thermal structure and composition using typical out-of-transit JWST observations. We found that using PIE with JWST should enable the stellar and planetary spectra to be disentangled with no degeneracies seen between the two flux sources, thus allowing robust constraints on the planet's night-side thermal structure and water abundance to be retrieved. The broad wavelength coverage achieved by combining spectra from NIRISS, NIRSpec, and MIRI enables PIE retrievals that are within 10% of the precision attained using traditional secondary eclipse measurements, although mid-IR observations with MIRI alone may face up to 3.5× lower precision on the planet's irradiation temperature. For non-transiting planets with unconstrained radius priors, we were able to identify and break the degeneracy between planet radius and irradiation temperature using data that resolved the peak of both the stellar and planetary spectra, thus potentially increasing the number of planets amenable to atmospheric characterization with JWST and other future mission concepts.

Keywords: exoplanet atmospheres; exoplanet atmospheric composition; astronomical methods; infrared excess
A Dynamical Survey of Stellar-mass Black Holes in 50 Milky Way Globular Clusters

Recent numerical simulations of globular clusters (GCs) have shown that stellar-mass black holes (BHs) play a fundamental role in driving cluster evolution and shaping their present-day structure. Rapidly mass-segregating to the center of GCs, BHs act as a dynamical energy source via repeated superelastic scattering, delaying the onset of core collapse and limiting mass segregation for visible stars. While recent discoveries of BH candidates in Galactic and extragalactic GCs have further piqued interest in BH-mediated cluster dynamics, numerical models show that even if significant BH populations remain in today's GCs, they are not typically in directly detectable configurations. We demonstrated in Weatherford et al. that an anticorrelation between a suitable measure of mass segregation (Δ) in observable stellar populations and the number of retained BHs in GC models can be applied to indirectly probe BH populations in real GCs. Here we estimate the number and total mass of BHs in 50 Milky Way GCs from the Advanced Camera for Surveys GC Survey. For each GC, Δ is measured between observed main-sequence populations and fed into correlations between Δ and BH retention found in our CMC Cluster Catalog's models. We demonstrate that the range in measured Δ from our models matches that for observed GCs to a remarkable degree. Our results constitute the largest sample of GCs for which BH populations have been predicted to date using a self-consistent and robust statistical approach. We identify NGC 2808, 5927, 5986, 6101, and 6205 to retain especially large BH populations, each with a total BH mass exceeding 103 ${M}_{\odot }$ .

Keywords: stellar mass black holes; globular star clusters; n-body simulations; computational methods; stellar kinematics; astrostatistics