adsabs/SciX_UAT_keywords huggingface dataset:
Shadow Implications: What Does Measuring the Photon Ring Imply for Gravity?

With the imaging and characterization of the horizon-scale images of M87* and Sgr A* by the Event Horizon Telescope (EHT), it has become possible to resolve the near-horizon region of astrophysical black holes. As a result, there has been considerable interest in the implications of the measurement of the shadow size, i.e., the asymptotic photon ring. We explore the general implications of such a measurement, identifying what is and, more importantly, is not constrained by such measurements, with applications to EHT and future instruments. We consider a general spherically symmetric metric, which effectively applies for a polar observer (appropriate for M87*) in the slow rotation limit. We propose a nonperturbative, nonparametric spacetime-domain characterization of shadow size and related measurements that makes explicit the nature and power (or lack thereof) of shadow-size-based constraints, and facilitates comparisons among observations and targets.

Keywords: black hole physics; very long baseline interferometry; strong gravitational lensing; gravitation
Magnetic Activity Evolution of Solar-like Stars. I. S ph-Age Relation Derived from Kepler Observations

The ages of solar-like stars have been at the center of many studies such as exoplanet characterization or Galactic-archeology. While ages are usually computed from stellar evolution models, relations linking ages to other stellar properties, such as rotation and magnetic activity, have been investigated. With the large catalog of 55,232 rotation periods, P rot, and photometric magnetic activity index, S ph from Kepler data, we have the opportunity to look for such magneto-gyro-chronology relations. Stellar ages are obtained with two stellar evolution codes that include treatment of angular momentum evolution, hence using P rot as input in addition to classical atmospheric parameters. We explore two different ways of predicting stellar ages on three subsamples with spectroscopic observations: solar analogs, late-F and G dwarfs, and K dwarfs. We first perform a Bayesian analysis to derive relations between S ph and ages between 1 and 5 Gyr, and other stellar properties. For late-F and G dwarfs, and K dwarfs, the multivariate regression favors the model with P rot and S ph with median differences of 0.1% and 0.2%, respectively. We also apply Machine Learning techniques with a Random Forest algorithm to predict ages up to 14 Gyr with the same set of input parameters. For late-F, G and K dwarfs together, predicted ages are on average within 5.3% of the model ages and improve to 3.1% when including P rot. These are very promising results for a quick age estimation for solar-like stars with photometric observations, especially with current and future space missions.

Keywords: asteroseismology; magnetic variable stars; stellar ages; stellar rotation
Beyond Simple AGN Unification with Chandra-observed 3CRR Sources at 0.5 < z < 1

Low-frequency radio selection finds radio-bright galaxies regardless of the amount of obscuration by gas and dust. We report Chandra observations of a complete 178 MHz-selected, and so orientation-unbiased, sample of 44 0.5 < z < 1 3CRR sources. The sample is comprised of quasars and narrow-line radio galaxies (NLRGs) with similar radio luminosities, and the radio structure serves as both an age and an orientation indicator. Consistent with unification, intrinsic obscuration (measured by NH, X-ray hardness ratio, and X-ray luminosity) generally increases with inclination. However, the sample includes a population not seen in high-z 3CRR sources: NLRGs viewed at intermediate inclination angles with NH < 1022 cm-2. Multiwavelength analysis suggests that these objects have lower L/LEdd than typical NLRGs at similar orientation. Thus, both orientation and L/LEdd are important, and a "radiation-regulated unification" provides a better explanation of the sample's observed properties. In comparison with the 3CRR sample at 1 < z < 2, our lower-redshift sample shows a higher fraction of Compton-thin NLRGs (45% versus 29%) but a similar Compton-thick fraction (20%), implying a larger covering factor of Compton-thin material at intermediate viewing angles and thus a more "puffed-up" torus atmosphere. We posit that this is due to a range of L/LEdd extending to lower values in this sample. In contrast, at high redshifts, the narrower range and high L/LEdd values allowed orientation (and so simple unification) to dominate the sample's observed properties.

Keywords: radio loud quasars; quasars; active galactic nuclei; x-ray quasars
The First JWST Spectral Energy Distribution of a Y Dwarf

We present the first JWST spectral energy distribution of a Y dwarf. This spectral energy distribution of the Y0 dwarf WISE J035934.06-540154.6 consists of low-resolution (λ/Δλ ~100) spectroscopy from 1-12 μm and three photometric points at 15, 18, and 21 μm. The spectrum exhibits numerous fundamental, overtone, and combination rotational-vibrational bands of H2O, CH4, CO, CO2, and NH3, including the previously unidentified ν 3 band of NH3 at 3 μm. Using a Rayleigh-Jeans tail to account for the flux emerging at wavelengths greater than 21 μm, we measure a bolometric luminosity of 1.523 ± 0.090 × 1020 W. We determine a semiempirical effective temperature estimate of ${467}_{-18}^{+16}$ K using the bolometric luminosity and evolutionary models to estimate a radius. Finally, we compare the spectrum and photometry to a grid of atmospheric models and find reasonably good agreement with a model having T eff = 450 K, log g = 3.25 [cm s-2], and [M/H] = -0.3. However, the low surface gravity implies an extremely low mass of 1 M Jup and a very young age of 20 Myr, the latter of which is inconsistent with simulations of volume-limited samples of cool brown dwarfs.

Keywords: brown dwarfs; stellar effective temperatures; y dwarfs; near infrared astronomy; spectroscopy
Micro-arcsecond Astrometry Technology: Detector and Field Distortion Calibration

Microarcsecond (μas) astrometry is an indispensable technique to detect earth-like exoplanets, fully characterize exoplanetary orbits, and measure their masses-information critical for assessing their habitability. Highly accurate astrometric measurements can also probe the nature of dark matter, the early universe, black holes, and neutron stars, thus providing unique data for new astrophysics. This paper presents technologies of calibrating detectors and field distortions for achieving narrow field μas relative astrometry with a focal plane array detector on a 6 m telescope.

Keywords: astrometry; calibration
Modeling the Quasiperiodic Radial Velocity Variations of γ Draconis

γ Draconis, a K5III star, showed radial velocity (RV) variations consistent with a 10.7 Jupiter mass planet from 2003 to 2011. After 2011, the periodic signal decayed, then reappeared with a phase shift. Hatzes et al. suggested that γ Dra's RV variations could come from oscillatory convective modes, but did not fit a mathematical model. Here we assess whether a quasi-periodic Gaussian process—appropriate when spots with finite lifetimes trace underlying periodicity—can explain the RVs. We find that a model with only one quasiperiodic signal is not adequate: we require a second component to fit the data. The best-fit model has quasi-periodic oscillations with P1 = 705 days and P2 = 15 days. The 705 day signal may be caused by magnetic activity. The 15 day period requires further investigation.

Keywords: exoplanets; radial velocity; exoplanet detection methods; stellar activity; bayesian statistics; gaussian processes regression; stellar rotation
Model-independent Mass Reconstruction of the Hubble Frontier Field Clusters with MARS Based on Self-consistent Strong-lensing Data

We present a new strong-lensing (SL) mass reconstruction of the six Hubble Frontier Fields (HFF) clusters with the MAximum-entropy ReconStruction (MARS) algorithm. MARS is a new free-form inversion method, which suppresses spurious small-scale fluctuations while achieving excellent convergence in positions of multiple images. For each HFF cluster, we obtain a model-independent mass distribution from the compilation of the self-consistent SL data in the literature. With 100-200 multiple images per cluster, we reconstruct solutions with small scatters of multiple images in both source (~0.″02) and image planes (0.″05-0.″1), which are lower than the previous results by a factor of 5-10. An outstanding case is the MACS J0416.1-2403 mass reconstruction, which is based on the largest high-quality SL data set where all 236 multiple images/knots have spectroscopic redshifts. Although our solution is smooth on a large scale, it reveals group/galaxy-scale peaks where the substructures are required by the data. We find that in general, these mass peaks are in excellent spatial agreement with the member galaxies, although MARS never uses the galaxy distributions as priors. Our study corroborates the flexibility and accuracy of the MARS algorithm and demonstrates that MARS is a powerful tool in the JWST era, when a 2-3 times larger number of multiple image candidates become available for SL mass reconstruction, and self-consistency within the data set becomes a critical issue.

Keywords: dark matter distribution; strong gravitational lensing; galaxy clusters
Spectroscopic Analysis of the Bulge Globular Cluster ESO 456-SC38

It has been suggested that the oldest stellar populations in the Milky Way are tightly bound and confined to the central regions of the Galaxy. This is one of the reasons why a handful of globular clusters located in the bulge region are thought to be remnants of the primeval formation stages of the Milky Way. The globular cluster, ESO 456-SC38 (Djorgovski 2), is one such cluster; it has a blue horizontal branch, is projected very close to the center of the Galaxy, and has an orbit confining it to the bulge/bar region. The first α abundances of seven stars in this heavily reddened cluster are presented using Apache Point Observatory Galaxy Evolution Experiment Data Release 16. A significant spread in the abundances of N, C, Na, and Al indicates the presence of multiple stellar populations in this cluster. Using Gaia DR2 proper motions and radial velocities from the Bulge Radial Velocity Assay for RR Lyrae stars, we confirm that RR Lyrae stars belong to this globular cluster. * Based on observations taken by APOGEE.

Keywords: globular star clusters; stellar astronomy; galactic bulge; milky way dynamics; chemical abundances; stellar abundances; stellar populations
A Survey of CO, CO2, and H2O in Comets and Centaurs

CO and CO2 are the two dominant carbon-bearing molecules in comae and have major roles in driving activity. Their relative abundances also provide strong observational constraints to models of solar system formation and evolution but have never been studied together in a large sample of comets. We carefully compiled and analyzed published measurements of simultaneous CO and CO2 production rates for 25 comets. Approximately half of the comae have substantially more CO2 than CO, about one-third are CO-dominated, and about 1/10 produce a comparable amount of both. There may be a heliocentric dependence to this ratio with CO dominating comae beyond 3.5 au. Eight out of nine of the Jupiter Family Comets in our study produce more CO2 than CO. The six dynamically new comets produce more CO2 relative to CO than the eight Oort Cloud comets that have made multiple passes through the inner solar system. This may be explained by long-term cosmic-ray processing of a comet nucleus's outer layers. We find (Q CO/Q ${}_{{{\rm{H}}}_{2}{\rm{O}}}$ )median = 3 ± 1% and (Q ${}_{{\mathrm{CO}}_{2}}$ /Q ${}_{{{\rm{H}}}_{2}{\rm{O}}}$ )median = 12 ± 2%. The inorganic volatile carbon budget was estimated to be (Q CO+Q ${}_{{\mathrm{CO}}_{2}}$ )/Q ${}_{{{\rm{H}}}_{2}{\rm{O}}}$ ~ 18% for most comets. Between 0.7 and 4.6 au, CO2 outgassing appears to be more intimately tied to the water production in a way that the CO is not. The volatile carbon/oxygen ratio for 18 comets is C/Omedian ~ 13%, which is consistent with a comet formation environment that is well within the CO snow line.

Keywords: comet origins; comet dynamics; comae; carbon dioxide
Accretion Disk Wind of Hercules X-1 during the Short High State

Hercules X-1 is a nearly edge-on X-ray binary with a warped, precessing accretion disk, which manifests through a 35-day cycle of alternating High and Low flux states. This disk precession introduces a changing line of sight toward the X-ray source, through an ionized accretion disk wind. The sightline variation allows us to uniquely determine how the wind properties vary with height above the disk. All the previous wind measurements were made in the brighter Main High state of Her X-1. Here, we analyze the only Chandra observation during the fainter "Short" High state and significantly detect blueshifted ionized absorption. We find a column density of ${2.0}_{-0.6}^{+1.1}\times {10}^{22}$ cm-2, an ionization parameter $\mathrm{log}(\xi $ /erg cm s-1) = ${3.41}_{-0.12}^{+0.15}$ , and an outflow velocity of 380 ± 40 km s-1. The properties of the outflow measured during the Short High state are in good agreement with those measured at equivalent precession phases during the Main High state. We conclude that we are sampling the same wind structure, seen during both the Main and Short High states, which is precessing alongside the warped accretion disk every 35 days. Finally, the high spectral resolution of Chandra gratings above 1 keV in this observation enabled us to measure the abundances of certain elements in the outflow. We find Mg/O $\,=\,{1.5}_{-0.4}^{+0.5}$ , Si/O =1.5 ± 0.4, and S/O $\,=\,{3.0}_{-1.1}^{+1.2}$ , whereas in our previous study of Her X-1 with XMM-Newton, we found an overabundance of N, Ne, and Fe compared with O. These peculiar abundance ratios were likely introduced by the pollution of the donor by the supernova that created Her X-1.

Keywords: accretion; x-ray binary stars; neutron stars
Fermi/GBM Observations of the SGRJ1935+2154 Burst Forest

During 2020 April and May, SGR J1935+2154 emitted hundreds of short bursts and became one of the most prolific transient magnetars. At the onset of the active bursting period, a 130 s burst "forest," which included some bursts with peculiar time profiles, were observed with the Fermi/Gamma-ray Burst Monitor (GBM). In this Letter, we present the results of time-resolved spectral analysis of this burst "forest" episode, which occurred on 2020 April 27. We identify thermal spectral components prevalent during the entire 130 s episode; high-energy maxima appear during the photon flux peaks, which are modulated by the spin period of the source. Moreover, the evolution of the νFν spectral hardness (represented by Epeak or blackbody temperature) within the lightcurve peaks is anti-correlated with the pulse phases extrapolated from the pulsation observed within the persistent soft X-ray emission of the source six hours later. Throughout the episode, the emitting area of the high-energy (hotter) component is 1-2 orders of magnitude smaller than that for the low-energy component. We interpret this with a geometrical viewing angle scenario, inferring that the high-energy component likely originates from a low-altitude hotspot located within closed toroidal magnetic field lines.

Keywords: magnetars; soft gamma-ray repeaters; x-ray bursters
Where Do Obscured AGN Fit in a Galaxy's Timeline?

Many X-ray bright active galactic nuclei (AGNs) are predicted to follow an extended stage of obscured black hole growth. In support of this picture we examine the X-ray undetected AGNs in the COSMOS field and compare their host galaxies with X-ray bright AGNs. We examine galaxies with M* > 109.5 M⊙ for the presence of AGNs at redshifts z = 0.5-3. We select AGNs in the infrared using Spitzer and Herschel detections and use color selection techniques to select AGNs within strongly star-forming hosts. We stack Chandra X-ray data of galaxies with an infrared (IR) detection but lacking an X-ray detection to obtain soft and hard fluxes, allowing us to measure the energetics of these AGNs. We find a clear correlation between X-ray luminosity and IR AGN luminosity in the stacked galaxies. We also find that X-ray undetected AGNs all lie on the main sequence-the tight correlation between the star formation rate and M* that holds for the majority of galaxies, regardless of mass or redshift. This work demonstrates that there is a higher population of obscured AGNs than previously thought.

Keywords: low-luminosity active galactic nuclei; x-ray active galactic nuclei; infrared astronomy; x-ray sources; galaxy evolution
Kiloparsec-scale Radio Structure in z 0.25 Radio-quiet QSOs

We present analysis of a homogeneous, optically selected, volume-limited (0.2 < z < 0.3) sample of 128 radio-quiet quasi-stellar objects (QSOs) recently observed at 6 GHz with the Very Large Array (VLA) in A configuration (~0.″33 resolution). We compare these new results to earlier (2010-2011) 6 GHz observations with the VLA in C configuration (~3.″5). While all of these radio-quiet QSOs (RQQs) were unresolved on a 3.″5 scale (~14 kpc at z = 0.25), we resolve notable complex subgalactic structures in about half of the RQQs at 0.″33 resolution (~1.3 kpc at z = 0.25). By comparison of flux density measurements between the two sets of observations, we demonstrate that significant sub-galactic-scale radio structure is present in at least 70% of the RQQ population and that the central component accounts for an average of ≈65% of the total detected radio power. One RQQ, J0935+4819, shows striking symmetric, double-lobed morphology and appears to be the first identified example of a radio-quiet QSO with FR II type morphology on ~arcsec scale (projected size of ≳6 kpc). In addition to revealing RQQ subgalactic morphology, we employ counterparts from legacy (FIRST at 1.4 GHz) and recent (VLA Sky Survey at 3 GHz) VLA surveys to investigate radio spectral indices and potential variability over decades-long timescales for a subset of the RQQs and for the cores of radio-intermediate and radio-loud sources in the parent sample of 178 QSOs. These results support the growing notion that the RQQ population is not a monolithic phenomenon but instead consists of a mixture of mainly starburst-powered and jet-powered galaxies.

Keywords: radio quiet quasars; active galaxies; direct imaging
Discovery of a Rare Eclipsing Be/X-Ray Binary System, Swift J010902.6-723710 = SXP 182

We report on the discovery of Swift J010902.6-723710, a rare eclipsing Be/X-ray Binary system by the Swift SMC Survey (S-CUBED). Swift J010902.6-723710 was discovered via weekly S-CUBED monitoring observations when it was observed to enter a state of X-ray outburst on 2023 October 10. X-ray emission was found to be modulated by a 182 s period. Optical spectroscopy is used to confirm the presence of a highly inclined circumstellar disk surrounding a B0-0.5Ve optical companion. Historical UV and IR photometry is then used to identify strong eclipse-like features reoccurring in both light curves with a 60.623 day period, which is adopted as the orbital period of the system. Eclipsing behavior is found to be the result of a large accretion disk surrounding the neutron star. Eclipses are produced when the disk passes in front of the OBe companion, blocking light from both the stellar surface and circumstellar disk. This is only the third Be/X-ray binary to have confirmed eclipses. We note that this rare behavior provides an important opportunity to constrain the physical parameters of a Be/X-ray binary with greater accuracy than is possible in noneclipsing systems.

Keywords: high mass x-ray binary stars; massive stars; x-ray binary stars; high energy astrophysics; eclipsing binary stars
Multidimensional Radiation Hydrodynamics Simulations of Pulsational Pair-instability Supernovae

Stars with masses of 80-130 M ⊙ can encounter pulsational pair-instability at the end of their lives, which triggers consecutive episodes of explosive burning that eject multiple massive shells. Collisions between these shells produce bright transients known as pulsational pair-instability supernovae (PPI SNe) that may explain some extreme supernovae. In this paper, we present the first 2D and 3D radiation hydrodynamics simulations of PPI SNe with the CASTRO code. Radiative cooling causes the collided shells to evolve into thin, dense structures with hot spots that can enhance the peak luminosity of the SN by factors of 2-3. The light curve peaks at 1.9-2.1 × 1043 erg s-1 for 50 days and then plateaus at 2-3 × 1042 erg s-1 for 200 days, depending on the viewing angle. The presence of 12C and 16O and the absence of 28Si and 56Fe in its spectra can uniquely identify this transient as a PPI SN in follow-up observations. Our models suggest that multidimensional radiation hydrodynamics is required to model the evolution and light curves of all shell-collision SNe, such as Type IIne, not just PPI SNe.

Keywords: supernovae; hydrodynamical simulations; shocks; massive stars; population iii stars; radiative transfer simulations; eruptive phenomena; astrophysical fluid dynamics; circumstellar shells; stellar structures; type ii supernovae
Study of the 27 Day Variations in GCR Fluxes during 2007-2008 Based on PAMELA and ARINA Observations

Using measurements from the PAMELA and ARINA spectrometers on board the Resurs-DK1 satellite, we have examined the 27 day intensity variations in galactic cosmic ray (GCR) proton fluxes in 2007-2008. The PAMELA and ARINA data allow for the first time a study of time profiles and the rigidity dependence of the 27 day variations observed directly in space in a wide rigidity range from ∼300 MV to several gigavolts. We find that the rigidity dependence of the amplitude of the 27 day GCR variations cannot be described by the same power law at both low and high energies. A flat interval occurs at rigidity $R=\langle 0.6\mbox{--}1.0\rangle $ GV with a power-law index γ = -0.13 ± 0.44 for PAMELA, whereas for R ≥ 1 GV, the power-law dependence is evident with index γ = -0.51 ± 0.11. We describe the rigidity dependence of the 27 day GCR variations for PAMELA and ARINA data in the framework of the modulation potential concept using the force-field approximation for GCR transport. For a physical interpretation, we have considered the relationship between the 27 day GCR variations and solar wind plasma and other heliospheric parameters. Moreover, we have discussed possible implications of MHD modeling of the solar wind plasma together with a stochastic GCR transport model concerning the effects of corotating interaction regions.

Keywords: galactic cosmic rays; heliosphere; corotating streams; solar wind