adsabs/SciX_UAT_keywords huggingface dataset:
Hidden Companions to Intermediate-mass Stars. VI. Discovery of a 0.50M ⊙, 6 au Companion to HIP 74696

A-type stars with a large long-term proper motion change and without a known companion to cause it are candidates for being Sirius analogues. However, in most cases the culprit is expected to be a hitherto unknown low mass companion rather than a white dwarf. Here we report the discovery of a 0.50M ⊙ companion to the nearby 1.64M ⊙ star HIP 74696 at a projected separation ρ = 118.9 mas ↔ 6.2 au based on a VLTI/GRAVITY observation. This companion explains the Gaia-Hipparcos proper motion change of the primary. Together with the wide 660 au companion that was found by Gaia DR3 to be a 0.70M ⊙ + 0.20M ⊙ 1.5 au binary, this makes HIP 74696 a quadruple and part of the growing class of high multiplicity systems with an A-type star primary. *Based on observations collected at the European Southern Observatory, Chile, Program ID 111.24UP.001.

Keywords: multiple stars; a stars; optical interferometry
Improving the Spatial Resolution of Solar Images Based on an Improved Conditional Denoising Diffusion Probability Model

The quality of solar images plays an important role in the analysis of small events in solar physics. Therefore, the improvement of image resolution based on super-resolution (SR) reconstruction technology has aroused the interest of many researchers. In this paper, an improved conditional denoising diffusion probability model (ICDDPM) based on the Markov chain is proposed for the SR reconstruction of solar images. This method reconstructs high-resolution (HR) images from low-resolution images by learning a reverse process that adds noise to HR images. To verify the effectiveness of the method, images from the Goode Solar Telescope at the Big Bear Solar Observatory and the Helioseismic and Magnetic Imager (HMI) on the Solar Dynamics Observatory are used to train a network, and the spatial resolution of reconstructed images is 4 times that of the original HMI images. The experimental results show that the performance based on ICDDPM is better than the previous work in subject judgment and object evaluation indexes. The reconstructed images of this method have higher subjective vision quality and better consistency with the HMI images. And the structural similarity and rms index results are also higher than the compared method, demonstrating the success of the resolution improvement using ICDDPM.

Keywords: solar photosphere; neural networks; solar active regions
New Insight into the Rapid Burster by Insight-HXMT

We report the timing and spectral analyses of the type-II X-ray bursts from the rapid burster (MXB 1730-335) observed by the Hard X-ray Modulation Telescope (Insight-HXMT) and Swift/X-Ray Telescope (XRT). By stacking the long-duration bursts, we find for the first time that the hard X-rays are lagging behind the soft X-rays by 3 s. However, such a lag is not visible for the short-duration bursts, probably because of the poor statistics. For all bursts the energy spectrum is found to be nonthermal, thanks to the broadband coverage of Insight-HXMT. These findings provide new insights into the type-II bursts and require a temporally visible corona for possible interpretation.

Keywords: x-ray bursters
High-redshift Galaxy Candidates at z = 9-10 as Revealed by JWST Observations of WHL0137-08

We report the discovery of four galaxy candidates observed 450-600 Myr after the Big Bang with photometric redshifts between z ~ 8.3 and 10.2 measured using James Webb Space Telescope (JWST) NIRCam imaging of the galaxy cluster WHL0137-08 observed in eight filters spanning 0.8-5.0 μm, plus nine Hubble Space Telescope filters spanning 0.4-1.7 μm. One candidate is gravitationally lensed with a magnification of μ ~ 8, while the other three are located in a nearby NIRCam module with expected magnifications of μ ≲ 1.1. Using SED fitting, we estimate the stellar masses of these galaxies are typically in the range $\mathrm{log}{M}_{\star }/{M}_{\odot }$ = 8.3-8.7. All appear young, with mass-weighted ages <240 Myr, low dust content A V < 0.15 mag, and specific star formation rates sSFR ~0.25-10 Gyr-1 for most. One z ~ 9 candidate is consistent with an age <5 Myr and an sSFR ~10 Gyr-1, as inferred from a strong F444W excess, implying [O III ]+H β rest-frame equivalent width ~2000 Å, although an older z ~ 10 object is also allowed. Another z ~ 9 candidate is lensed into an arc 2.″4 long with a magnification of μ ~ 8. This arc is the most spatially resolved galaxy at z ~ 9 known to date, revealing structures ~30 pc across. Follow-up spectroscopy of WHL0137-08 with JWST/NIRSpec will be useful to spectroscopically confirm these high-redshift galaxy candidates and to study their physical properties in more detail.

Keywords: high-redshift galaxies; galaxy clusters; strong gravitational lensing
Scaling K2. I. Revised Parameters for 222,088 K2 Stars and a K2 Planet Radius Valley at 1.9 R⊕

Previous measurements of stellar properties for K2 stars in the Ecliptic Plane Input Catalog largely relied on photometry and proper motion measurements, with some added information from available spectra and parallaxes. Combining Gaia DR2 distances with spectroscopic measurements of effective temperatures, surface gravities, and metallicities from the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) DR5, we computed updated stellar radii and masses for 26,838 K2 stars. For 195,250 targets without a LAMOST spectrum, we derived stellar parameters using random forest regression on photometric colors trained on the LAMOST sample. In total, we measured spectral types, effective temperatures, surface gravities, metallicities, radii, and masses for 222,088 A, F, G, K, and M-type K2 stars. With these new stellar radii, we performed a simple reanalysis of 299 confirmed and 517 candidate K2 planet radii from Campaigns 1-13, elucidating a distinct planet radius valley around 1.9 R⊕, a feature thus far only conclusively identified with Kepler planets, and tentatively identified with K2 planets. These updated stellar parameters are a crucial step in the process toward computing K2 planet occurrence rates.

Keywords: fundamental parameters of stars; exoplanet systems; exoplanets
Nonthermal Atmospheric Escape on the Kepler-11 "Super-Earths" Driven by Stellar Wind Sputtering

Jeans escape or hydrodynamic escape is believed to dominate atmospheric loss for hot Jupiters. However, nonthermal mechanisms likely contribute substantially on hydrogen-rich "super-Earths" with relatively cold and extended atmospheres. This study is devoted to investigating the role of stellar wind sputtering on Kepler-11b-f, with the aid of Monte Carlo test particle calculations. Such a mechanism is widely known to be important on many solar system bodies, but its impact has never been evaluated rigorously on any exoplanet. Our calculations reveal complicated variations of the H sputtering yield with the stellar wind inclination angle and neutral heating efficiency at different Kepler-11 planets. Further calculations suggest the H loss rates on Kepler-11b-f to be 2.8 × 106-1.5 × 108 g s-1, driven by stellar wind sputtering. The H loss rate obtained here is compared to those driven by other mechanisms, indicating that the importance of stellar wind sputtering is highly variable and this mechanism could induce a large atmospheric loss rate comparable to the blow-off rate driven by stellar far-ultraviolet radiation, in particular for planets with relatively low gravities.

Keywords: exoplanet atmospheres; exoplanet atmospheric evolution; planetary atmospheres
The Geographic Distribution of Dense-phase O2 on Ganymede

Ground-based spectroscopy of Ganymede's surface has revealed the surprising presence of dense-phase molecular oxygen (O2) via weak absorptions at visible wavelengths. To date, the state and stability of this O2 at the temperatures and pressures of Ganymede's surface are not understood. Its spatial distribution in relation to albedo, expected temperatures, particle irradiation patterns, or composition may provide clues to these unknowns. We present spatially resolved observations of Ganymede's surface O2 obtained with the Hubble Space Telescope and construct the first comprehensive map of its geography. In agreement with the limited spatially resolved data published previously, our map suggests that the condensed O2 is concentrated at the low to midlatitudes of the trailing hemisphere, a distribution that may reflect influences of Ganymede's intrinsic magnetic field on the bombardment of its surface by Jovian magnetospheric particles. Overlapping regions from different observations within this data set also show evidence for moderate temporal variability in the surface O2, but we are unable to distinguish between potential causes with the available data.

Keywords: galilean satellites; ganymede; surface composition; planetary surfaces
Organic Chemistry in the H2-bearing, CO-rich Interstellar Ice Layer at Temperatures Relevant to Dense Cloud Interiors

Ice chemistry in the dense, cold interstellar medium (ISM) is probably responsible for the formation of interstellar complex organic molecules (COMs). Recent laboratory experiments performed at T ∼ 4 K have shown that irradiation of CO:N2 ice samples analog to the CO-rich interstellar ice layer can contribute to the formation of COMs when H2 molecules are present. We have tested this organic chemistry under a broader range of conditions relevant to the interior of dense clouds by irradiating CO:15N2:H2 ice samples with 2 keV electrons in the 4–15 K temperature range. The H2 ice abundance depended on both, the ice formation temperature and the thermal evolution of the samples. Formation of H-bearing organics such as formaldehyde (H2CO), ketene (C2H2O), and isocyanic acid (H15NCO) was observed upon irradiation of ice samples formed at temperatures up to 10 K, and also in ices formed at 6 K and subsequently warmed up and irradiated at temperatures up to 15 K. These results suggest that a fraction of the H2 molecules in dense cloud interiors might be entrapped in the CO-rich layer of interstellar ice mantles, and that energetic processing of this layer could entail an additional contribution to the formation of COMs in the coldest regions of the ISM.

Keywords: interstellar medium; interstellar clouds; interstellar molecules; dense interstellar clouds; ice composition; complex organic molecules; cosmic rays
Spitzer Microlensing Parallax Reveals Two Isolated Stars in the Galactic Bulge

We report the mass and distance measurements of two single-lens events from the 2017 Spitzer microlensing campaign. The ground-based observations yield the detection of finite-source effects, and the microlens parallaxes are derived from the joint analysis of ground-based observations and Spitzer observations. We find that the lens of OGLE-2017-BLG-1254 is a 0.60 ± 0.03 M⊙ star with DLS = 0.53 ± 0.11 kpc, where DLS is the distance between the lens and the source. The second event, OGLE-2017-BLG-1161, is subject to the known satellite parallax degeneracy, and thus is either a 0.51-0.10+0.12 M_{⊙} star with DLS = 0.40 ± 0.12 kpc or a 0.38-0.12+0.13 M_{⊙} star with DLS = 0.53 ± 0.19 kpc. Both of the lenses are therefore isolated stars in the Galactic bulge. By comparing the mass and distance distributions of the eight published Spitzer finite-source events with the expectations from a Galactic model, we find that the Spitzer sample is in agreement with the probability of finite-source effects occurring in single-lens events.

Keywords: gravitational microlensing; satellite microlensing parallax; stellar masses; stellar distance
The KMOS3D Survey: Investigating the Origin of the Elevated Electron Densities in Star-forming Galaxies at 1 ≲ z ≲ 3

We investigate what drives the redshift evolution of the typical electron density (ne) in star-forming galaxies, using a sample of 140 galaxies drawn primarily from KMOS3D (0.6 < z < 2.6) and 471 galaxies from SAMI (z < 0.113). We select galaxies that do not show evidence of active galactic nucleus activity or outflows to constrain the average conditions within H II regions. Measurements of the [S II]λ6716/[S II]λ6731 ratio in four redshift bins indicate that the local ne in the line-emitting material decreases from 187 ${}_{-132}^{+140}$ cm-3 at z ∼ 2.2 to 32 ${}_{-9}^{+4}$ cm-3 at z ∼ 0, consistent with previous results. We use the Hα luminosity to estimate the rms ne averaged over the volumes of star-forming disks at each redshift. The local and volume-averaged ne evolve at similar rates, hinting that the volume filling factor of the line-emitting gas may be approximately constant across 0 ≲ z ≲ 2.6. The KMOS3D and SAMI galaxies follow a roughly monotonic trend between ne and star formation rate, but the KMOS3D galaxies have systematically higher ne than the SAMI galaxies at a fixed offset from the star-forming main sequence, suggesting a link between the ne evolution and the evolving main sequence normalization. We quantitatively test potential drivers of the density evolution and find that ne(rms) $\simeq {n}_{{{\rm{H}}}_{2}}$ , suggesting that the elevated ne in high-z H II regions could plausibly be the direct result of higher densities in the parent molecular clouds. There is also tentative evidence that ne could be influenced by the balance between stellar feedback, which drives the expansion of H II regions, and the ambient pressure, which resists their expansion.

Keywords: galaxy evolution; high-redshift galaxies; interstellar medium
Real-time Technosignature Strategies with SN 2023ixf

Several technosignature techniques focus on historic events such as SN 1987A as the basis to search for coordinated signal broadcasts from extraterrestrial agents. The recently discovered SN 2023ixf in the spiral galaxy M101 is the nearest Type II supernova in over a decade, and will serve as an important benchmark event. Here we review the potential for SN 2023ixf to advance ongoing techonsignature searches, particularly signal-synchronization techniques such as the "SETI Ellipsoid" that identifies over time stars that could transmit signals after observing a supernovae event. We find that more than 100 stars within 100 pc are already close to intersecting this SETI Ellipsoid, providing numerous targets for real-time monitoring within ~3° of SN 2023ixf. We are commencing a radio technosignature monitoring campaign of these targets with the Allen Telescope Array and the Green Bank Telescope.

Keywords: search for extraterrestrial intelligence; technosignatures; type ii supernovae; core-collapse supernovae
Biased Tracer Reconstruction with Halo Mass Information

Plenty of crucial information about our universe is encoded in the cosmic large-scale structure (LSS). However, extractions of this information are usually hindered by the nonlinearities of the LSS, which can be largely alleviated by various techniques known as reconstruction. In realistic applications, the efficiencies of these methods are always degraded by many limiting factors, a quite important one being the shot noise induced by the finite number density of biased matter tracers (i.e., luminous galaxies or dark matter halos) in observations. In this work, we explore the gains of biased tracer reconstruction achieved from halo mass information, which can suppress the shot-noise component and dramatically improves the cross-correlation between tracer field and dark matter. To this end, we first closely study the clustering biases and the stochasticity properties of halo fields with various number densities under different weighting schemes, i.e., the uniform, mass, and optimal weightings. Then, we apply the biased tracer reconstruction method to these different weighted halo fields and investigate how linear bias and observational mass scatter affect the reconstruction performance. Our results demonstrate that halo masses are critical information for significantly improving the performance of biased tracer reconstruction, indicating great application potential for substantially promoting the precision of cosmological measurements (especially for baryon acoustic oscillations) in ambitious ongoing and future galaxy surveys.

Keywords: cosmology; large-scale structure of the universe; baryon acoustic oscillations
Orbital and Atmospheric Characterization of the 1RXS J034231.8+121622 System using High-resolution Spectroscopy Confirms that the Companion is a Low-mass Star

The 1RXS J034231.8+121622 system consists of an M dwarf primary and a directly imaged low-mass stellar companion. We use high-resolution spectroscopic data from Keck/KPIC to estimate the objects' atmospheric parameters and radial velocities (RVs). Using PHOENIX stellar models, we find that the primary has a temperature of 3460 ± 50 K and a metallicity of 0.16 ± 0.04, while the secondary has a temperature of 2510 ± 50 K and a metallicity of ${0.13}_{-0.11}^{+0.12}$ . Recent work suggests this system is associated with the Hyades, giving it an older age than previous estimates. Both metallicities agree with current Hyades [Fe/H] measurements (0.11–0.21). Using stellar evolutionary models, we obtain significantly higher masses for the objects, 0.30 ± 0.15 M ⊙ and 0.08 ± 0.01 M ⊙ (84 ± 11 M Jup), respectively. Using the RVs and a new astrometry point from Keck/NIRC2, we find that the system is likely an edge-on, moderately eccentric ( ${0.41}_{-0.08}^{+0.27}$ ) configuration. We also estimate the C/O ratio of both objects using custom grid models, obtaining 0.42 ± 0.10 (primary) and 0.55 ± 0.10 (companion). From these results, we confirm that this system most likely went through a binary star formation process in the Hyades. The significant changes in this system's parameters since its discovery highlight the importance of high-resolution spectroscopy for both orbital and atmospheric characterization of directly imaged companions.

Keywords: brown dwarfs; direct imaging; high resolution spectroscopy; exoplanets; binary stars; orbit determination; atmospheric composition; star formation; exoplanet formation
Measuring Turbulence with Young Stars in the Orion Complex

Stars form in molecular clouds in the interstellar medium (ISM) with a turbulent kinematic state. Newborn stars therefore should retain the turbulent kinematics of their natal clouds. Gaia DR2 and APOGEE-2 surveys in combination provide three-dimensional (3D) positions and 3D velocities of young stars in the Orion Molecular Cloud Complex. Using the full 6D measurements, we compute the velocity structure functions (VSFs) of the stars in six different groups within the Orion Complex. We find that the motions of stars in all diffuse groups exhibit strong characteristics of turbulence. Their first-order VSFs have a power-law exponent ranging from ∼0.2-0.5 on scales of a few to a few tens of parsecs, generally consistent with Larson's relation. On the other hand, dense star clusters, such as the Orion Nebula Cluster (ONC), have experienced rapid dynamical relaxation, and have lost the memory of the initial turbulent kinematics. The VSFs of several individual groups and the whole Complex all show features supporting local energy injection from supernovae. The measured strength of turbulence depends on the location relative to the supernova epicenters and the formation history of the groups. Our detection of turbulence traced by young stars introduces a new method of probing the turbulent kinematics of the ISM. Unlike previous gas-based studies with only projected measurements accessible to observations, we utilize the full 6D information of stars, presenting a more complete picture of the 3D interstellar turbulence.

Keywords: molecular clouds; stellar dynamics; young star clusters; interstellar medium; stellar feedback; supernova remnants; stellar motion
Elemental Abundances in M31: Gradients in the Giant Stellar Stream

We analyze existing measurements of [Fe/H] and [α/Fe] for individual red giant branch (RGB) stars in the Giant Stellar Stream (GSS) of M31 to determine whether spatial abundance gradients are present. These measurements were obtained from low- (R ~ 3000) and moderate- (R ~ 6000) resolution Keck/DEIMOS spectroscopy using spectral synthesis techniques as part of the Elemental Abundances in M31 survey. From a sample of 62 RGB stars spanning the GSS at 17, 22, and 33 projected kpc, we measure a [Fe/H] gradient of -0.018 ± 0.003 dex kpc-1 and negligible [α/Fe] gradient with M31-centric radius. We investigate GSS abundance patterns in the outer halo using additional [Fe/H] and [α/Fe] measurements for six RGB stars located along the stream at 45 and 58 projected kpc. These abundances provide tentative evidence that the trends in [Fe/H] and [α/Fe] beyond 40 kpc in the GSS are consistent with those within 33 kpc. We also compare the GSS abundances to 65 RGB stars located along the possibly related Southeast (SE) shelf substructure at 12 and 18 projected kpc. The abundances of the GSS and SE shelf are consistent, supporting a common origin hypothesis, although this interpretation may be complicated by the presence of [Fe/H] gradients in the GSS. We discuss the abundance patterns in the context of photometric studies from the literature and explore implications for the properties of the GSS progenitor, suggesting that the high ⟨[α/Fe]⟩ of the GSS (+0.40 ± 0.05 dex) favors a major merger scenario for its formation. * 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: stellar abundances; galaxy abundances; stellar streams; galaxy stellar halos; andromeda galaxy; galaxy formation
How Do Magnetic Field Models Affect Astrophysical Limits on Light Axion-like Particles? An X-Ray Case Study with NGC 1275

Axion-like particles (ALPs) are a well-motivated extension to the standard model of particle physics, and X-ray observations of cluster-hosted AGN currently place the most stringent constraints on the ALP coupling to electromagnetism, g a γ , for very light ALPs (m a ≲ 10-11 eV). We revisit limits obtained by Reynolds et al. using Chandra X-ray grating spectroscopy of NGC 1275, the central AGN in the Perseus cluster, examining the impact of the X-ray spectral model and magnetic field model. We also present a new publicly available code, ALPRO, which we use to solve the ALP propagation problem. We discuss evidence for turbulent magnetic fields in Perseus and show that it can be important to resolve the magnetic field structure on scales below the coherence length. We reanalyze the NGC 1275 X-ray spectra using an improved data reduction and baseline spectral model. We find the limits are insensitive to whether a partially covering absorber is used in the fits. At low m a (m a ≲ 10-13 eV), we find marginally weaker limits on g a γ (by 0.1-0.3 dex) with different magnetic field models, compared to Model B from Reynolds et al. (2020). A Gaussian random field (GRF) model designed to mimic ~50 kpc scale coherent structures also results in only slightly weaker limits. We conclude that the existing Model B limits are robust assuming that β pl ≈ 100, and are insensitive to whether cell-based or GRF methods are used. However, astrophysical uncertainties regarding the strength and structure of cluster magnetic fields persist, motivating high-sensitivity RM observations and tighter constraints on the radial profile of β pl.

Keywords: particle astrophysics; dark matter; x-ray active galactic nuclei; intracluster medium; extragalactic magnetic fields