adsabs/SciX_UAT_keywords huggingface dataset:
A Search for Stellar Siblings of the 200 Myr TOI-251 b Planetary System

Young planets (<1 Gyr) are helpful for studying the physical processes occurring at the early stage of planet evolution. TOI-251 b is a recently discovered sub-Neptune orbiting a young G dwarf, which has an imprecise age estimation of 40-320 Myr. We select TOI-251 sibling candidates based on kinematics and spatial proximity to TOI-251 and further use the color-magnitude diagram to refine the list and to compare to multiple open clusters. We report the stellar rotational period for 321 sibling candidates in a 50 pc radius around TOI-251 by analyzing their stellar light curves and find a color-rotational period sequence that lies in between the Group X (300 Myr) and Pleiades (120 Myr) members, suggesting an age ~ 200 Myr. A quantitative age analysis using gyrochronology relations gives 204 ± 45 Myr, consistent with the average Li age of selected siblings (238 ± 38 Myr) and the Gaia variability age (193 ${}_{-54}^{102}$ Myr). The detection fraction of comoving candidates that have a short rotational period is 68.1%, much higher than the typical value in the field (14%-16% from Kepler). The overdensity of young stars and consistency in age of stellar siblings suggest a potential young association candidate in the Phoenix-Grus constellation. Though TOI-251 b has a radius larger than most of its field-age counterparts, we are uncertain whether TOI-251 is inflated, due to a lack of knowledge on the planet's mass.

Keywords: stellar associations; exoplanet evolution; early stellar evolution; stellar dynamics; stellar ages; stellar rotation
Internetwork Magnetic Fields Seen in Fe I 1564.8 nm Full-disk Images

We studied the properties of internetwork magnetic fields in the solar photosphere, taking advantage of full-disk Stokes V/I maps of the Fe I 1564.8 nm line, which were obtained during 2010-2019. In contrast to most previous studies, we used data with moderate spatial and spectral resolutions. Nonetheless, we were able to distinguish the internetwork field components and the active region/network boundary components using large Zeeman splitting of the Fe I 1564.8 nm line. Thus, our analysis provides a point of view quite different from that of previous studies. We analyzed the data statistically without ordinary inversions, yet we successfully derived some properties of internetwork fields; the internetwork is filled with small-scale magnetic fields, their strength is within the weak field regime of the Fe I 1564.8 nm line (300-400 G or less), and the internetwork fields are highly inclined. Although the results were obtained from the analysis performed from a different perspective, they are consistent with the majority of previous findings. In addition, no notable variation in the properties of the internetwork fields was found during the period covering most of solar cycle 24.

Keywords: solar photosphere; solar magnetic fields; near infrared astronomy; spectropolarimetry
Photospheric Polarization Signatures from Long Gamma-Ray Burst Simulations

A comprehensive understanding of gamma-ray bursts (GRBs) has been elusive due to the variety of questions surrounding the radiation mechanism at play in these events. Polarization measurements of GRBs can heavily constrain the relevant radiation mechanisms and the structure of the GRB jet; however, there is a limited number of theoretical predictions that observed GRB polarizations can be compared against. Here, we conduct radiative transfer calculations of a set of two-dimensional relativistic hydrodynamic long GRB (LGRB) jet simulations, of a constant and a variable jet, using the Monte Carlo Radiation Transport (MCRaT) code. MCRaT has been enhanced by the inclusion of polarization; it has been first verified by reproducing a variety of results in the literature and then used to obtain the time-integrated and time-resolved polarization degrees and angles of the synthetic LGRBs. While the obtained time-integrated polarization degrees (≲1%) are consistent with the constraints from the POLAR experiment, they are lower than other theoretical studies due to the lack of strong gradients in the model jet profiles that we use. The time-resolved results suggests that GRBs with wide jets observed on axis will have small polarization degrees (≲2%) and constant polarization angles, during the brightest portion of the light curve. GRBs observed off-axis will have larger polarization degrees and polarization angles that change with the temporal structure of radiating shells in the outflow. We then place our results in the context of GRB prompt emission models and future LEAP and POLAR-2 GRB polarimetry detections.

Keywords: gamma-ray bursts; hydrodynamics; radiative transfer simulations
Evolution of Solar Eruptive Events: Investigating the Relationships among Magnetic Reconnection, Flare Energy Release, and Coronal Mass Ejections

We study the evolution of solar eruptive events by investigating the temporal relationships among magnetic reconnection, flare energy release, and the acceleration of coronal mass ejections (CMEs). Leveraging the optimal viewing geometry of the Solar TErrestrial RElations Observatory (STEREO) relative to the Solar Dynamics Observatory (SDO) and the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) during 2010-2013, we identify 12 events with sufficient spatial and temporal coverage for a detailed examination. STEREO and SDO data are used to measure the CME kinematics and the reconnection rate, respectively, and hard X-ray (HXR) measurements from RHESSI provide a signature of the flare energy release. This analysis expands upon previous solar eruptive event timing studies by examining the fast-varying features, or "bursts," in the HXR and reconnection rate profiles, which represent episodes of energy release. Through a time lag correlation analysis, we find that HXR bursts occur throughout the main CME acceleration phase for most events, with the HXR bursts lagging the acceleration by 2 ± 9 minutes for fast CMEs. Additionally, we identify a nearly one-to-one correspondence between bursts in the HXR and reconnection rate profiles, with HXRs lagging the reconnection rate by 1.4 ± 2.8 minutes. The studied events fall into two categories: events with a single dominant HXR burst and events with a train of multiple HXR bursts. Events with multiple HXR bursts, indicative of intermittent reconnection and/or particle acceleration, are found to correspond with faster CMEs.

Keywords: solar flares; solar x-ray flares; solar activity; solar coronal mass ejections; solar magnetic reconnection; time series analysis
Far-ultraviolet Dust Extinction and Molecular Hydrogen in the Diffuse Milky Way Interstellar Medium

We aim to compare variations in the full-UV dust extinction curve (912-3000 Å), with the H I/H2/total H content along diffuse Milky Way sightlines, to investigate possible connections between ISM conditions and dust properties. We combine an existing sample of 75 UV extinction curves based on IUE and FUSE data, with atomic and molecular column densities measured through UV absorption. The H2 column density data are based on existing Lyman-Werner absorption band models from earlier work on the extinction curves. Literature values for the H I column density were compiled, and improved for 23 stars by fitting a Lyα profile to archived spectra. We discover a strong correlation between the H2 column and the far-UV extinction, and the underlying cause is a linear relationship between H2 and the strength of the far-UV rise feature. This extinction does not scale with H I, and the total H column scales best with $A\left(V\right)$ instead. The carrier of the far-UV rise therefore coincides with molecular gas, and further connections are shown by comparing the UV extinction features to the molecular fraction. Variations in the gas-to-extinction ratio $N({\rm{H}})/A\left(V\right)$ correlate with the UV-to-optical extinction ratio, and we speculate this could be due to coagulation or shattering effects. Based on the H2 temperature, the strongest far-UV rise strengths are found to appear in colder and denser sightlines.

Keywords: interstellar dust extinction; interstellar absorption; diffuse molecular clouds; ultraviolet spectroscopy; interstellar medium; neutral hydrogen clouds; dust composition
Smallest Scale Clumpy Star Formation in Stephan's Quintet Revealed from UV and IR Imaging

The spatial distribution and physical sizes of star-forming clumps at the smallest scales provide valuable information on hierarchical star formation (SF). In this context, we report the sites of ongoing SF at ~120 pc along the interacting galaxies in Stephan's Quintet compact group using AstroSat-UVIT and JWST data. Since ultraviolet radiation is a direct tracer of recent SF, we identified star-forming clumps in this compact group from the FUV imaging which we used to guide us to detect star-forming regions on JWST IR images. The FUV imaging reveals star-forming regions within which we detect smaller clumps from the higher spatial resolution images of JWST, likely produced by PAH molecules and dust ionized by FUV emission from young massive stars. This analysis reveals the importance of FUV imaging data in identifying star-forming regions in the highest spatial resolution IR imaging available.

Keywords: star formation; ultraviolet astronomy
Survey of X-Rays from Massive Stars Observed at High Spectral Resolution with Chandra

Identifying trends between observational data and the range of physical parameters of massive stars is a critical step to the still-elusive full understanding of the source, structure, and evolution of X-ray emission from the stellar winds, requiring a substantial sample size and systematic analysis methods. As of 2022, the Chandra data archive contains 37 high-resolution spectra of O, B, and WR stars, observed with the Chandra/HETGS, and of sufficient quality to fit the continua and emission-line profiles. Using a systematic approach to the data analysis, we explore morphological trends in the line profiles (i.e., O, Ne, Mg, and Si) and find that the centroid offsets of resolved lines versus wavelength can be separated in three empirically defined groups based on the amount of line broadening and centroid offset. Using Fe XVII (15.01, 17.05 Å) and Ne X α (12.13 Å) lines, which are prevalent among the sample stars, we find a well-correlated linear trend of increasing Full Width Half Maximum with faster wind terminal velocity. The H-like/He-like total line flux ratio for strong lines displays different trends with spectral class depending on ion species. Some of the sources in our sample have peculiar properties (e.g., magnetic and γ Cas-analog stars) and we find that these sources stand out as outliers from more regular trends. Finally, our spectral analysis is presented summarily in terms of X-ray spectral energy distributions in specific luminosity for each source, including tables of line identifications and fluxes.

Keywords: high resolution spectroscopy; massive stars; x-ray stars
Chemical Evolution in the Milky Way: Rotation-based Ages for APOGEE-Kepler Cool Dwarf Stars

We use models of stellar angular momentum evolution to determine ages for ∼500 stars in the APOGEE-Kepler Cool Dwarfs sample. We focus on lower-main-sequence stars, where other age-dating tools become ineffective. Our age distributions are compared to those derived from asteroseismic and giant samples and solar analogs. We are able to recover gyrochronological ages for old, lower-main-sequence stars, a remarkable improvement over prior work in hotter stars. Under our model assumptions, our ages have a median relative uncertainty of 14%, comparable to the age precision inferred for more massive stars using traditional methods. We investigate trends of Galactic α-enhancement with age, finding evidence of a detection threshold between the age of the oldest α-poor stars and that of the bulk α-rich population. We argue that gyrochronology is an effective tool reaching ages of 10-12 Gyr in K and early M dwarfs. Finally, we present the first effort to quantify the impact of detailed abundance patterns on rotational evolution. We estimate a ∼15% bias in age for cool, α-enhanced (+0.4 dex) stars when standard solar-abundance-pattern rotational models are used for age inference, rather than models that appropriately account for α-enrichment.

Keywords: stellar rotation; stellar ages; stellar evolution; galaxy chemical evolution
Cool Cores in Clusters of Galaxies in the Dark Energy Survey

We search for the presence of cool cores in optically selected galaxy clusters from the Dark Energy Survey (DES) and investigate their prevalence as a function of redshift and cluster richness. Clusters were selected from the redMaPPer analysis of three years of DES observations that have archival Chandra X-ray observations, giving a sample of 99 clusters with a redshift range of 0.11 < z < 0.87 and a richness range of 25 < λ < 207. Using the X-ray data, the core temperature was compared to the outer temperature to identify clusters where the core temperature is a factor of 0.7 or less than the outer temperature. We found a cool core fraction of approximately 20% with no significant trend in the cool core fraction with either redshift or richness.

Keywords: galaxy clusters; cooling flows; intracluster medium
A Low Cost 4 bit 16 Giga-sample-per-second Analog-to-digital Converter for Radio Astronomy

In this study, a 4 bit, 16 giga samples per second analog-to-digital converter (ADC) printed circuit board assembly (PCBA) was designed, manufactured, and characterized for digitizing signals from radio telescopes. For this purpose, an Adsantec ANST7123-KMA flash ADC chip was used. Because this design of chip is not followed the serial ADC JESD204 standard completely, we used a novel channel bonding scheme developed in our previous project for the high-speed serial data input alignment. The PCBA was equipped with a field-programmable gate array (FPGA) mezzanine card (FMC) connector. FMC allowed us to use the FPGA evaluation board by Xilinx as the testing platform. The PCBA enables data acquisition with a wide bandwidth and simplifies the intermediate frequency section. In the current version, the PCBA and the chip exhibit an analog bandwidth of 16 GHz, which facilitates a second Nyquist sampling. The following minimum to maximum performance parameters were obtained from the first and second Nyquist zones: a spurious-free dynamic range of 18-33 dB and an effective number of bits of 2.1-3.7 bits. The board will be ported to the Collaboration for Astronomy Signal Processing and Electronics Research environment, which is open for use by non-profit scientific teams, including the Event Horizon Telescope.

Keywords: radio astronomy
The ALFALFA-SDSS Galaxy Catalog

We present a H I optical catalog of ∼30,000 galaxies based on the 100% complete Arecibo Legacy Fast Arecibo L-band Feed Array (ALFALFA) survey combined with data from the Sloan Digital Sky Survey (SDSS). Our goal is to facilitate the public use of the completed ALFALFA catalog by providing carefully determined matches to SDSS counterparts, including matches for ∼10,000 galaxies that do not have SDSS spectra. These identifications can provide a basis for further crossmatching with other surveys using SDSS photometric IDs as a reference point. We derive absolute magnitudes and stellar masses for each galaxy using optical colors combined with an internal reddening correction designed for small- and intermediate-mass galaxies with active star formation. We also provide measures of stellar masses and star formation rates based on infrared and/or ultraviolet photometry for galaxies that are detected by the Wide-field Infrared Survey Explorer and/or the Galaxy Evolution Explorer. Finally, we compare the galaxy population in the ALFALFA-SDSS sample with the populations in several other publicly available galaxy catalogs and confirm that ALFALFA galaxies typically have lower masses and bluer colors.

Keywords: galaxies; late-type galaxies; galaxy evolution; sky surveys; astronomy databases
Dust Grains Cannot Grow to Millimeter Sizes in Protostellar Envelopes

A big question in the field of star and planet formation is the time at which substantial dust grain growth occurs. The observed properties of dust emission across different wavelength ranges have been used as an indication that millimeter-sized grains are already present in the envelopes of young protostars. However, this interpretation is in tension with results from coagulation simulations, which are not able to produce such large grains in these conditions. In this work, we show analytically that the production of millimeter-sized grains in protostellar envelopes is impossible under the standard assumptions about the coagulation process. We discuss several possibilities that may serve to explain the observed dust emission in the absence of in situ grain growth to millimeter sizes.

Keywords: dust physics; star forming regions; planet formation
A Comprehensive Study of Hα Emitters at z ∼ 0.62 in the DAWN Survey: The Need for Deep and Wide Regions

We present new estimates of the luminosity function (LF) and star formation rate density (SFRD) for an Hα-selected sample at z ∼ 0.62 from the Deep And Wide Narrow-band (DAWN) survey. Our results are based on a new Hα sample in the extended COSMOS region (compared to Coughlin et al.) with the inclusion of flanking fields, resulting in a total area coverage of ∼1.5 deg2. A total of 241 Hα emitters were selected based on robust selection criteria using spectrophotometric redshifts and broadband color-color classification. Given that dust extinction is a dominant uncertainty in the estimation of LF and SFRD, we explore the effect of different dust-correction prescriptions by calculating the LF and SFRD using a constant dust extinction correction, AHα = 1 mag, a luminosity-dependent correction, and a stellar-mass-dependent correction. The resulting Hα LFs are well fitted using Schechter functions with best-fit parameters: L* = 1042.24 erg s-1, φ* = 10-2.85 Mpc-3, α = -1.62 for constant dust correction, L*=1042.31 erg s-1, φ* = 10-2.8 Mpc-3, α = -1.39 for luminosity-dependent dust correction, and L* = 1042.36 erg s-1, φ* = 10-2.91 Mpc-3, α = -1.48, for stellar-mass-dependent dust correction. The deep and wide nature of the DAWN survey effectively samples Hα emitters over a wide range of luminosities, thereby providing better constraints on both the faint and bright ends of the LF. Also, the SFRD estimates ρSFR = 10-1.39 M⊙ yr-1 Mpc-3 (constant dust correction), ρSFR = 10-1.47 M⊙ yr-1 Mpc-3 (luminosity-dependent dust correction), and ρSFR = 10-1.46 M⊙ yr-1 Mpc-3 (stellar-mass-dependent dust correction) are in good agreement with the evolution of SFRD across redshifts (0 < z < 2) seen from previous Hα surveys.

Keywords: emission line galaxies; star formation; star forming regions; luminosity function
Insight into the Formation of β Pic b through the Composition of Its Parent Protoplanetary Disk as Revealed by the β Pic Moving Group Member HD 181327

It has been suggested that β Pic b has a supersolar metallicity and subsolar C/O ratio. Assuming solar carbon and oxygen abundances for the star β Pic and therefore the planet's parent protoplanetary disk, β Pic b's C/O ratio suggests that it formed via core accretion between its parent protoplanetary disk's H2O and CO2 ice lines. However, β Pic b's high metallicity is difficult to reconcile with its mass M p = 11.7 M Jup. Massive stars can present peculiar photospheric abundances that are unlikely to record the abundances of their former protoplanetary disks. This issue can be overcome for early-type stars in moving groups by inferring the elemental abundances of the FGK stars in the same moving group that formed in the same molecular cloud and presumably share the same composition. We infer the photospheric abundances of the F dwarf HD 181327, a β Pic moving group member that is the best available proxy for the composition of β Pic b's parent protoplanetary disk. In parallel, we infer updated atmospheric abundances for β Pic b. As expected for a planet of its mass formed via core-accretion beyond its parent protoplanetary disk's H2O ice line, we find that β Pic b's atmosphere is consistent with stellar metallicity and confirm that it has superstellar carbon and oxygen abundances with a substellar C/O ratio. We propose that the elemental abundances of FGK dwarfs in moving groups can be used as proxies for the otherwise difficult-to-infer elemental abundances of early-type and late-type members of the same moving groups.

Keywords: exoplanet astronomy; exoplanet atmospheres; exoplanet atmospheric composition; exoplanet formation; exoplanet migration; exoplanet systems; planet hosting stars; stellar abundances
From out of the Blue: Swift Links 2002es-like, 2003fg-like, and Early Time Bump Type Ia Supernovae

We collect a sample of 42 Type Ia supernovae (SNe Ia) with Swift UV photometry and well-measured early time light-curve rises and find that 2002es-like and 2003fg-like SNe Ia have different prepeak UV color evolutions compared to normal SNe Ia and other spectroscopic subtypes. Specifically, 2002es-like and 2003fg-like SNe Ia are cleanly separated from other SNe Ia subtypes by UVM2 ‑ UVW1 ≳ 1.0 mag at t = ‑ 10 days relative to B-band maximum. Furthermore, the SNe Ia that exhibit nonmonotonic bumps in their rising light curves, to date, consist solely of 2002es-like and 2003fg-like SNe Ia. We also find that SNe Ia with two-component power-law rises are more luminous than SNe Ia with single-component power-law rises at prepeak epochs. Given the similar UV colors, along with other observational similarities, we discuss a possible progenitor scenario that places 2002es-like and 2003fg-like SNe Ia along a continuum and may explain the unique UV colors, early time bumps, and other observational similarities between these objects. Ultimately, further observations of both subtypes, especially in the near-infrared, are critical for constraining models of these peculiar thermonuclear explosions.

Keywords: type ia supernovae
Symbiotic Stars in the Apache Point Observatory Galactic Evolution Experiment Survey: The Case of LIN 358 and SMC N73 (LIN 445a)

LIN 358 and SMC N73 are two symbiotic binaries in the halo of the Small Magellanic Cloud, each composed of a hot white dwarf accreting from a cool giant companion. In this work, we characterize these systems using a combination of spectral energy distribution (SED)-fitting to the extant photometric data spanning a broad wavelength range (X-ray/ultraviolet to near-infrared), detailed analysis of the Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectra for the giant stars, and orbit fitting to high quality radial velocities from the APOGEE database. Using the calculated Roche lobe radius for the giant component and the mass ratio for each system, it is found that LIN 358 is likely undergoing mass transfer via wind Roche lobe overflow, while the accretion mechanism for SMC N73 remains uncertain. This work presents the first orbital characterization for both of these systems (yielding periods of >270 and >980 days, respectively, for SMC N73 and LIN 358) and the first global SED fitting for SMC N73. In addition, variability was identified in APOGEE spectra of LIN 358 spanning 17 epochs over two years that may point to a time variable accretion rate as the product of an eccentric orbit.

Keywords: symbiotic binary stars