adsabs/SciX_UAT_keywords huggingface dataset:
Probing the Efficiency of Tidal Synchronization in Outspiralling Double White Dwarf Binaries with LISA

Compact-object binaries including a white dwarf component are unique among gravitational-wave sources because their evolution is governed not just by general relativity and tides, but also by mass transfer. While the black hole and neutron star binaries observed with ground-based gravitational-wave detectors are driven to inspiral due to the emission of gravitational radiation-manifesting as a "chirp-like" gravitational-wave signal-the astrophysical processes at work in double white dwarf (DWD) systems can cause the inspiral to stall and even reverse into an outspiral. The dynamics of the DWD outspiral thus encode information about tides, which tell us about the behavior of electron-degenerate matter. We carry out a population study to determine the effect of the strength of tides on the distributions of the DWD binary parameters that the Laser Interferometer Space Antenna (LISA) will be able to constrain. We find that the strength of tidal coupling parameterized via the tidal synchronization timescale at the onset of mass transfer affects the distribution of gravitational-wave frequencies and frequency derivatives for detectably mass-transferring DWD systems. Using a hierarchical Bayesian framework informed by binary population synthesis simulations, we demonstrate how this parameter can be inferred using LISA observations. By measuring the population properties of DWDs, LISA will be able to probe the behavior of electron-degenerate matter.

Keywords: white dwarf stars; am canum venaticorum stars; semi-detached binary stars; gravitational wave sources; tides; accretion
Retrieving the C and O Abundances of HR 7672 AB: A Solar-type Primary Star with a Benchmark Brown Dwarf

A benchmark brown dwarf (BD) is a BD whose properties (e.g., mass and chemical composition) are precisely and independently measured. Benchmark BDs are valuable in testing theoretical evolutionary tracks, spectral synthesis, and atmospheric retrievals for substellar objects. Here, we report results of atmospheric retrieval on a synthetic spectrum and a benchmark BD, HR 7672 B, with petitRADTRANS. First, we test the retrieval framework on a synthetic PHOENIX BT-Settl spectrum with a solar composition. We show that the retrieved C and O abundances are consistent with solar values, but the retrieved C/O is overestimated by 0.13-0.18, which is about four times higher than the formal error bar. Second, we perform retrieval on HR 7672 B using high spectral-resolution data (R = 35,000) from the Keck Planet Imager and Characterizer and near-infrared photometry. We retrieve [C/H], [O/H], and C/O to be -0.24 ± 0.05, -0.19 ± 0.04, and 0.52 ± 0.02. These values are consistent with those of HR 7672 A within 1.5σ. As such, HR 7672 B is among only a few benchmark BDs (along with Gl 570 D and HD 3651 B) that have been demonstrated to have consistent elemental abundances with their primary stars. Our work provides a practical procedure of testing and performing atmospheric retrieval, and sheds light on potential systematics of future retrievals using high- and low-resolution data.

Keywords: exoplanet atmospheric composition; brown dwarfs; chemical abundances
Toward Atmospheric Retrievals of Panchromatic Light Curves: EXPLOR-ing Generalized Inversion Techniques for Transiting Exoplanets with JWST and Ariel

Conventional atmospheric retrieval codes are designed to extract information, such as chemical abundances, thermal structures, and cloud properties, from fully "reduced" spectra obtained during transit or eclipse. Reduced spectra, however, are assembled by fitting a series of simplified light curves to time-series observations, wavelength by wavelength. Thus, spectra are postprocessed summary statistics of the original data, which by definition do not encode all the available information (i.e., astrophysical signal, model covariance, and instrumental noise). Here, we explore an alternative inversion strategy where the atmospheric retrieval is performed on the light curve directly, i.e., closer to the data. This method is implemented in EXoplanet Panchromatic Light curve Observation and Retrieval (EXPLOR), a novel atmospheric retrieval code inheriting from the TAUREX project. By explicitly considering time in the model, EXPLOR naturally handles transits, eclipses, phase curves, and other complex geometries for transiting exoplanets. In this paper, we have validated this new technique by inverting simulated panchromatic light curves. The model was tested on realistic simulations of a WASP-43 b-like exoplanet as observed with the James Webb Space Telescope (JWST) and Ariel telescope. By comparing our panchromatic light-curve approach against conventional spectral retrievals on mock scenarios, we have identified key breaking points in information and noise propagation when employing past literature techniques. Throughout the paper, we discuss the importance of developing "closer-to-data" approaches such as the method presented in this work, and highlight the inevitable increase in model complexity and computing requirements associated with the recent JWST revolution.

Keywords: exoplanet atmospheres; astronomy data analysis; james webb space telescope; time series analysis
Characterizing Observed Extra Mixing Trends in Red Giants using the Reduced Density Ratio from Thermohaline Models

Observations show an almost ubiquitous presence of extra mixing in low-mass upper giant branch stars. The most commonly invoked explanation for this is thermohaline mixing. One-dimensional stellar evolution models include various prescriptions for thermohaline mixing, but the use of observational data directly to discriminate between thermohaline prescriptions has thus far been limited. Here, we propose a new framework to facilitate direct comparison: using carbon-to-nitrogen measurements from the Sloan Digital Sky Survey-IV APOGEE survey as a probe of mixing and a fluid parameter known as the reduced density ratio from one-dimensional stellar evolution programs, we compare the observed amount of extra mixing on the upper giant branch to predicted trends from three-dimensional fluid dynamics simulations. Using this method, we are able to empirically constrain how mixing efficiency should vary with the reduced density ratio. We find the observed amount of extra mixing is strongly correlated with the reduced density ratio and that trends between reduced density ratio and fundamental stellar parameters are robust across choices for modeling prescription. We show that stars with available mixing data tend to have relatively low density ratios, which should inform the regimes selected for future simulation efforts. Finally, we show that there is increased mixing at low reduced density ratios, which is consistent with current hydrodynamical models of thermohaline mixing. The introduction of this framework sets a new standard for theoretical modeling efforts, as validation for not only the amount of extra mixing, but trends between the degree of extra mixing and fundamental stellar parameters is now possible.

Keywords: stellar evolution; stellar abundances; abundance ratios; stellar interiors; red giant branch; red giant bump; dredge-up; hydrodynamics; astrophysical fluid dynamics
Magnetic Field Structure in Spheroidal Star-forming Clouds. II. Estimating Field Structure from Observed Maps

This paper presents models to estimate the structure of density and magnetic field strength in spheroidal condensations from maps of their column density and their polarization of magnetically aligned dust grains. The density model is obtained by fitting a column density map with an embedded p = 2 Plummer spheroid of any aspect ratio and inclination. The magnetic properties are based on the density model, the Davis-Chandrasekhar-Fermi (DCF) model of Alfvénic fluctuations, and the spheroid flux freezing (SFF) model of mass and flux conservation in Paper I. The field strength model has the resolution of the column density map, which is finer than the resolution of the DCF estimate of field strength. The models are applied to ALMA observations of the envelope of the protostar BHR 71 IRS1. Column density fits give the density model from (2.0 ± 0.4) × 105 to (7 ± 1) × 107 cm-3. The density model predicts the field directions map, which fits the polarization map best within 1100 au, with standard deviation of angle differences of 17°. In this region, the DCF mean field strength is 0.7 ± 0.2 mG, and the envelope mass is supercritical, with a ratio of mass to magnetic critical mass of 1.5 ± 0.4. The SFF field strength profile scales with the DCF field strength from 60 ± 10 μG to 3 ± 1 mG. The spatial resolution of the SFF field strength estimate is finer than the DCF resolution by a factor of ∼7, and the peak SFF field strength exceeds the DCF field strength by a factor of ∼4.

Keywords: interstellar magnetic fields; star formation
Black Hole Ultracompact X-Ray Binaries: Galactic Low-frequency Gravitational Wave Sources

In the Galaxy, close binaries with compact objects are important low-frequency gravitational wave (GW) sources. As potential low-frequency GW sources, neutron star/white dwarf (WD) ultracompact X-ray binaries (UCXBs) have been investigated extensively. Using the Modules for Experiments in Stellar Astrophysics code, we systematically explored the evolution of black hole (BH)-main-sequence star (MS) binaries to determine whether their descendants can be detected by space-borne GW detectors. Our simulations showed that BH-MS binaries with an initial orbital period less than the bifurcation period can evolve into BH UCXBs that can be detected by LISA. Such an evolutionary channel would form compact mass-transferring BH-WD systems rather than detached BH-WD systems. The calculated X-ray luminosities of BH UCXBs that can be detected by LISA at a distance d = 1 kpc are ~1033-1035 erg s-1 (~1034-1035 erg s-1 for d = 10 kpc); hence, it is possible to detect their electromagnetic counterparts. It is worth emphasizing that only some BH-MS systems with an initial orbital period very close to the bifurcation period can evolve toward low-frequency GW sources whose chirp masses can be measured. The maximum GW frequency of BH UCXBs forming via the BH-MS pathway is about 3 mHz, which is smaller than the minimum GW frequency (6.4 mHz) of mass-transferring BH-WDs originating from a dynamic process. Furthermore, we obtain an initial parameter space (donor-star masses and orbital periods) of progenitors of BH UCXB-GW sources, which can be applied to future population synthesis simulations. By a rough estimation, we predict that LISA would only be able to detect a few BH UCXB-GW sources formed by the BH-MS channel.

Keywords: black holes; white dwarf stars; gravitational wave sources; x-ray binary stars; stellar evolution
Simultaneous NICER and NuSTAR Observations of the Ultracompact X-Ray Binary 4U 1543-624

We present the first joint NuSTAR and NICER observations of the ultracompact X-ray binary (UCXB) 4U 1543-624 obtained in 2020 April. The source was at a luminosity of L0.5-50 keV = 4.9(D/7 kpc)2 × 1036 erg s-1 and showed evidence of reflected emission in the form of an O VIII line, Fe K line, and Compton hump within the spectrum. We used a full reflection model, known as XILLVERCO, that is tailored for the atypical abundances found in UCXBs, to account for the reflected emission. We tested the emission radii of the O and Fe line components and conclude that they originate from a common disk radius in the innermost region of the accretion disk (Rin ≤ 1.07 RISCO). Assuming that the compact accretor is a neutron star (NS) and the position of the inner disk is the Alfvén radius, we placed an upper limit on the magnetic field strength to be B ≤ 0.7(D/7 kpc) × 108 G at the poles. Given the lack of pulsations detected and position of Rin, it was likely that a boundary layer region had formed between the NS surface and inner edge of the accretion disk with an extent of 1.2 km. This implies a maximum radius of the neutron star accretor of RNS ≤ 12.1 km when assuming a canonical NS mass of 1.4 M⊙.

Keywords: accretion; low-mass x-ray binary stars
Magnetic Fields Observed by Voyager 2 in the Heliosheath

We present observations of the magnetic field ${\boldsymbol{B}}$ in the outermost region of the heliosheath made by Voyager 2 (V2) from 2016 to 2018.6, just before V2 entered the magnetic barrier inside of the heliopause. The average magnetic field strength (B) during this interval was relatively large, 0.135 nT, mainly due to numerous merged interaction regions. Sector structure was observed, and the direction of azimuthal angle λ was primarily close to the Parker spiral magnetic field directions 90° and 270°. Thus, the heliospheric current sheet extended to relatively high southern latitudes poleward of V2 (>30°). On smaller scales, distributions of daily increments in B and the components of ${\boldsymbol{B}}$ from 2016 to 2018.6 were accurately described by q-Gaussian distributions. The average values of the nonextensivity parameter q for one-day increments of the components decreased from q = 1.7 ± 0.01 during 2016 (near solar maximum) to q = 1.3 ± 0.1 during 2017 and 2018, as solar activity declined. The BT direction was close to the average magnetic field direction, and V2 measured primarily compressible fluctuations. These new results are also presented in the context of an overview of the observations of the magnetic field in the heliosheath from the termination shock crossing to the heliopause.

Keywords: heliosheath; magnetic fields
Understanding the Planetary Formation and Evolution in Star Clusters (UPiC). I. Evidence of Hot Giant Exoplanets Formation Timescales

Planets in young star clusters could shed light on planet formation and evolution since star clusters can provide accurate age estimation. However, the number of transiting planets detected in clusters was only ~30, too small for statistical analysis. Thanks to the unprecedented high-precision astrometric data provided by Gaia DR2 and Gaia DR3, many new open clusters (OCs) and comoving groups have been identified. The Understanding Planetary Formation and Evolution in Star Clusters project aims to find observational evidence and interpret how planets form and evolve in cluster environments. In this work, we cross match the stellar catalogs of new OCs and comoving groups with confirmed planets and candidates. We carefully remove false positives and obtain the biggest catalog of planets in star clusters up to now, which consists of 73 confirmed planets and 84 planet candidates. After age validation, we obtain the radius-age diagram of these planets/candidates. We find an increment in the fraction of hot Jupiters (HJs) around 100 Myr and attribute the increment to the flyby-induced high-e migration in star clusters. An additional small bump of the fraction of HJs after 1 Gyr is detected, which indicates the formation timescale of HJ around field stars is much larger than that in star clusters. Thus, stellar environments play important roles in the formation of HJs. The hot Neptune desert occurs around 100 Myr in our sample. A combination of photoevaporation and high-e migration may sculpt the hot Neptune desert in clusters.

Keywords: exoplanet catalogs; exoplanets; exoplanet evolution; open star clusters; astrostatistics
Exploring the Possible Evolution of the Mass Density Power-law Index of Strong Gravitational Lenses with a Model-independent Method

In this work, we adopt a cosmological model-independent approach for the first time to test the question of whether the mass density power-law index (γ) of strong gravitational lensing systems (SGLSs) evolves with redshift, and the joint light-curve Type Ia supernova (SNe Ia) sample and the quasar sample from Risaliti & Lusso are used to provide the luminosity distances to be calibrated. Our work is based on the flat universe assumption and the cosmic distance duality relation. A reliable data-matching method is used to pair SGLS-SNe and SGLS-quasars. By using the maximum likelihood method to constrain the luminosity distance and γ index, we obtain the likelihood function values for the evolved and nonevolved cases, and then use the Akaike weights and the Bayesian Information Criterion (BIC) selection weights to compare the advantages and disadvantages of these two cases. We find that the γ index is slightly more likely to be a nonevolutionary model for γ = 2 in the case of the currently used samples with low redshift (z l < ~ 0.66). With Akaike weights, the relative probabilities are 66.3% versus 33.7% and 69.9% versus 30.1% for the SGLS + SNe Ia sample and SGLS + quasar sample, respectively, and with the BIC selection weights, the relative probabilities are 87.4% versus 12.6% and 52.0% versus 48.0% for the two samples. In the evolving case for the relatively low-redshift lenses (SGLS + SNe Ia), with redshift 0.0625-0.659, $\gamma ={2.058}_{-0.040}^{+0.041}\mbox{--}{0.136}_{-0.165}^{+0.163}z$ . At high redshift (SGLS + quasar), with redshift 0.0625-1.004, $\gamma \,={2.051}_{-0.077}^{+0.076}\mbox{--}{0.171}_{-0.196}^{+0.214}z$ . Although not the more likely model, this evolved γ case also fits the data well, with a negative and mild evolution for both low- and high-redshift samples.

Keywords: strong gravitational lensing; quasars; supernovae
Short GRB Host Galaxies. II. A Legacy Sample of Redshifts, Stellar Population Properties, and Implications for Their Neutron Star Merger Origins

We present the stellar population properties of 69 short gamma-ray burst (GRB) host galaxies, representing the largest uniformly modeled sample to date. Using the Prospector stellar population inference code, we jointly fit photometry and/or spectroscopy of each host galaxy. We find a population median redshift of $z={0.64}_{-0.32}^{+0.83}$ (68% confidence), including nine photometric redshifts at z ≳ 1. We further find a median mass-weighted age of t m = ${0.8}_{-0.53}^{+2.71}$ Gyr, stellar mass of log(M */M ⊙) = ${9.69}_{-0.65}^{+0.75}$ , star formation rate of SFR = ${1.44}_{-1.35}^{+9.37}$ M ⊙ yr-1, stellar metallicity of log(Z */Z ⊙) = $-{0.38}_{-0.42}^{+0.44}$ , and dust attenuation of ${A}_{V}={0.43}_{-0.36}^{+0.85}$ mag (68% confidence). Overall, the majority of short GRB hosts are star-forming (≈84%), with small fractions that are either transitioning (≈6%) or quiescent (≈10%); however, we observe a much larger fraction (≈40%) of quiescent and transitioning hosts at z ≲ 0.25, commensurate with galaxy evolution. We find that short GRB hosts populate the star-forming main sequence of normal field galaxies, but do not include as many high-mass galaxies as the general galaxy population, implying that their binary neutron star (BNS) merger progenitors are dependent on a combination of host star formation and stellar mass. The distribution of ages and redshifts implies a broad delay-time distribution, with a fast-merging channel at z > 1 and a decreased neutron star binary formation efficiency from high to low redshifts. If short GRB hosts are representative of BNS merger hosts within the horizon of current gravitational wave detectors, these results can inform future searches for electromagnetic counterparts. All of the data and modeling products are available on the Broadband Repository for Investigating Gamma-ray burst Host Traits website.

Keywords: gravitational wave sources; gamma-ray bursts; stellar populations
CO(J = 1 - 0) Observations toward the Filamentary Cloud in the Galactic Region of 153.°60 ≤ l ≤ 156.°50 and 1.°85 ≤ b ≤ 3.°50

We present observations of the J = 1 - 0 transition lines of 12CO, 13CO, and C18O toward the Galactic region of 153.°60 ≤ l ≤ 156.°50 and 1.°85 ≤ b ≤ 3.°50, using the Purple Mountain Observatory 13.7 m millimeter telescope. Based on the 13CO data, one main filament and five subfilaments are found together as a network structure in the velocity interval of [-42.5, -30.0] km s-1. The kinematic distance of this molecular cloud is estimated to be ~4.5 kpc. The median length, width, excitation temperature, and line mass of these filaments are ~49 pc, ~2.9 pc, ~8.9 K, and ~39 M ⊙ pc-1, respectively. The velocity structures along these filaments exhibit oscillatory patterns, which are likely caused by the fragmentation or accretion process along these filaments. The maximum accretion rate is estimated to be ~700 M ⊙ pc-1. A total of ~162 13CO clumps and ~103 young stellar objects are identified in this region. Most of the clumps are in gravitationally bound states. Three H II regions (G154.359+2.606, SH2-211, and SH2-212) are found to be located in the apexes of the filaments. Intense star-forming activity is found along the entire filamentary cloud. The observed results may help us to better understand the link between filaments and massive star formation.

Keywords: molecular clouds; interstellar filaments; star forming regions; young stellar objects
Connecting Galactic Outflows and Star Formation: Inferences from Hα Maps and Absorption-line Spectroscopy at 1 ≲ z ≲ 1.5

We investigate the connection between galactic outflows and star formation using two independent data sets covering a sample of 22 galaxies between 1 ≲ z ≲ 1.5. The Hubble Space Telescope WFC3/G141 grism provides low spectral resolution, high spatial resolution spectroscopy yielding Hα emission-line maps from which we measure the spatial extent and strength of star formation. In the rest-frame near-UV, Keck/DEIMOS observes Fe II and Mg II interstellar absorption lines, which provide constraints on the intensity and velocity of the outflows. We compare outflow properties from individual and composite spectra with the star formation rate (SFR) and SFR surface density (ΣSFR), as well as the stellar mass and specific SFR (sSFR). The Fe II and Mg II equivalent widths (EWs) increase with both SFR and ΣSFR at ≳3σ significance, while the composite spectra show larger Fe II EWs and outflow velocities in galaxies with higher SFR, ΣSFR, and sSFR. Absorption-line profiles of the composite spectra further indicate that the differences between subsamples are driven by outflows rather than the interstellar medium. While these results are consistent with those of previous studies, the use of Hα images makes them the most direct test of the relationship between star formation and outflows at z > 1 to date. Future facilities such as the James Webb Space Telescope and the upcoming Extremely Large Telescopes will extend these direct, Hα-based studies to lower masses and SFRs, probing galactic feedback across orders of magnitude in galaxy properties and augmenting the correlations we find here. * This work is based in part on observations taken by the 3D-HST Treasury Program (GO 12177 and 12328) with the NASA/ESA Hubble Space Telescope, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. † Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

Keywords: galaxy evolution; galaxy formation; high-redshift galaxies; starburst galaxies