adsabs/SciX_UAT_keywords huggingface dataset:
LBT Reveals Large Dust Particles and a High Mass-loss Rate for K2-22 b

The disintegrating planet candidate K2-22 b shows periodic and stochastic transits best explained by an escaping debris cloud. However, the mechanism that creates the debris cloud is unknown. The grain size of the debris as well as its sublimation rate can be helpful in understanding the environment that disintegrates the planet. Here, we present simultaneous photometry with the g band at 0.48 μm and KS band at 2.1 μm using the Large Binocular Telescope. During an event with very low dust activity, we put a new upper limit on the size of the planet of 0.71 R⊕ or 4500 km. We also detected a medium depth transit that can be used to constrain the dust particle sizes. We find that the median particle size must be larger than about 0.5-1.0 μm, depending on the composition of the debris. This leads to a high mass-loss rate of about 3 × 108 kg s-1, which is consistent with hydrodynamic escape models. If they are produced by some alternate mechanism such as explosive volcanism, it would require extraordinary geological activity. Combining our upper limits on the planet size with the high mass-loss rate, we find a lifetime of the planet of less than 370 Myr. This drops to just 21 Myr when adopting the 0.02 M⊕ mass predicted from hydrodynamical models.

Keywords: exoplanet astronomy; transmission spectroscopy; extrasolar rocky planets; exoplanet atmospheric composition; exoplanet surface composition; multi-color photometry
The Next Generation Virgo Cluster Survey. XXXIII. Stellar Population Gradients in the Virgo Cluster Core Globular Cluster System

We present a study of the stellar populations of globular clusters (GCs) in the Virgo Cluster core with a homogeneous spectroscopic catalog of 692 GCs within a major-axis distance R maj = 840 kpc from M87. We investigate radial and azimuthal variations in the mean age, total metallicity, [Fe/H], and α-element abundance of blue (metal-poor) and red (metal-rich) GCs using their co-added spectra. We find that the blue GCs have a steep radial gradient in [Z/H] within R maj = 165 kpc, with roughly equal contributions from [Fe/H] and [α/Fe], and flat gradients beyond. By contrast, the red GCs show a much shallower gradient in [Z/H], which is entirely driven by [Fe/H]. We use GC-tagged Illustris simulations to demonstrate an accretion scenario where more massive satellites (with more metal- and α-rich GCs) sink further into the central galaxy than less massive ones, and where the gradient flattening occurs because of the low GC occupation fraction of low-mass dwarfs disrupted at larger distances. The dense environment around M87 may also cause the steep [α/Fe] gradient of the blue GCs, mirroring what is seen in the dwarf galaxy population. The progenitors of red GCs have a narrower mass range than those of blue GCs, which makes their gradients shallower. We also explore spatial inhomogeneity in GC abundances, finding that the red GCs to the northwest of M87 are slightly more metal-rich. Future observations of GC stellar population gradients will be useful diagnostics of halo merger histories.

Keywords: globular star clusters; chemical abundances; virgo cluster; stellar populations; giant elliptical galaxies; galaxy clusters
Photometric Observations of Nine High Mass X-Ray Binaries and Analysis of Potential Periodicities and Variations

Beginning with American Association of Variable Star Observers Alert Notice 348 (2007 April 6) and being continually extended and updated through 2020 April 17 with Alert Notice 377, Dr. Gordon Sarty requested continuing assistance with his ongoing radial velocity observations of High Mass X-Ray Binaries. As of Alert Notice 377, nine targets were identified. These are: 1H 1936+541, RX J2030.5+4751, V2175 Cyg, V1008 Cep, V831 Cas, RX J0440.9+4431/LS V+44 17, V420 Aur, HD 249179, and SAX J0635+0533. While these Alert Notices prioritized radial velocity observations with the objective of determining orbital periods of these binary systems, optical photometry can also reveal other periods and variations due to mass transfer, pulsations, rotations, spin rates, and other effects. This Research Note will address in more detail the observation and analysis of one of these nine High Mass X-Ray Binaries, specifically 1H 1936+541.

Keywords: high mass x-ray binary stars
Circumnuclear Molecular Gas in Low-redshift Quasars and Matched Star-forming Galaxies

A series of gravitational instabilities in a circumnuclear gas disk (CND) are required to trigger gas transport to a central supermassive black hole and ignite active galactic nuclei (AGNs). A test of this scenario is to investigate whether an enhanced molecular gas mass surface density (Σmol) is found in the CND-scale of quasars relative to a comparison sample of inactive galaxies. Here we performed subkiloparsec resolution CO(2-1) observations with the Atacama Large Millimeter/submillimeter Array (ALMA) of four low-redshift (z ∼ 0.06), luminous (∼1045 erg s-1) quasars with each matched to a different star-forming galaxy, having similar redshift, stellar mass, and star formation rate. We detected CO(2-1) emission from all quasars, which show diverse morphologies. Contrary to expectations, Σmol of the quasar sample, computed from the CO(2-1) luminosity, tends to be smaller than the comparison sample at r < 500 pc; there is no systematic enhancement of Σmol in our quasars. We discuss four possible scenarios that would explain the lower molecular gas content (or CO(2-1) luminosity as an actual observable) at the CND-scale of quasars, i.e., AGN-driven outflows, gas-rich minor mergers, time-delay between the onsets of a starburst-phase and a quasar-phase, and X-ray-dominated region (XDR) effects on the gas chemical abundance and excitation. While not extensively discussed in the literature, XDR effects can have an impact on molecular mass measurements particularly in the vicinity of luminous quasar nuclei; therefore higher resolution molecular gas observations, which are now viable using ALMA, need to be considered.

Keywords: quasars; active galactic nuclei; supermassive black holes; submillimeter astronomy; molecular gas; star formation
Age Analysis of Extrasolar Planets: Insight from Stellar Isochrone Models

There is growing evidence from stellar kinematics and galactic chemical evolution suggesting that giant planets (M P ≥ 0.3M J ) are relatively young compared to the most commonly occurring population of small planets (M P < 0.3M J ). To further test the validity of these results, we analyzed the ages for a large number of 2336 exoplanet hosting stars determined using three different but well-established isochrone fitting models, namely, PARSEC, MIST, and Yonsei Yale. As input parameters, we used Gaia DR3 parallaxes, magnitudes, and photometric temperature, as well as spectroscopically determined more accurate temperatures and metallicities from the Sweet Catalog. Our analysis suggests that ∼50%–70% of stars with planets are younger than the Sun. We also find that, among the confirmed exoplanetary systems, stars hosting giant planets are even younger compared to small planet hosts. The median age of ∼2.61–3.48 Gyr estimated for the giant planet-hosting stars (depending on the model input parameters) suggests that the later chemical enrichment of the galaxy by the iron-peak elements, largely produced from Type Ia supernovae, may have paved the way for the formation of gas giants. Furthermore, within the giant planet population itself, stars hosting hot Jupiters (orbital period ≤10 days) are found to be younger compared to the stellar hosts of cool and warm Jupiters (orbital period >10 days), implying that hot Jupiters could be the youngest systems to emerge in the progression of planet formation.

Keywords: stellar ages; exoplanet formation; planet hosting stars; extrasolar gaseous giant planets; exoplanets; hot jupiters
The M Supergiant High-mass X-Ray Binary 4U 1954+31

The X-ray binary 4U 1954+31 has been classified as a low-mass X-ray binary containing an M giant and a neutron star (NS). It has also been included in the rare class of X-ray symbiotic binaries. The Gaia parallax, infrared colors, spectral type, abundances, and orbital properties of the M star demonstrate that the cool star in this system is not a low-mass giant but a high-mass M supergiant. Thus, 4U 1954+31 is a high-mass X-ray binary (HMXB) containing a late-type supergiant. It is the only known binary system of this type. The mass of the M I is ${9}_{-2}^{+6}$ M⊙ giving an age of this system in the range 12-50 Myr with the NS no more than 43 Myr old. The spin period of the NS is one of the longest known, 5 hr. The existence of M I plus NS binary systems is in accord with stellar evolution theory, with this system a more evolved member of the HMXB population.

Keywords: x-ray binary stars; late-type supergiant stars; stellar abundances; late stellar evolution
Cosmicflows-3: The South Pole Wall

Velocity and density field reconstructions of the volume of the universe within 0.05c derived from the Cosmicflows-3 catalog of galaxy distances has revealed the presence of a filamentary structure extending across ∼0.11c. The structure, at a characteristic redshift of 12,000 km s-1, has a density peak coincident with the celestial South Pole. This structure, the largest contiguous feature in the local volume and comparable to the Sloan Great Wall at half the distance, is given the name the South Pole Wall.

Keywords: large-scale structure of the universe; cosmology
Temporal Analysis of GRB Precursors in the Third Swift-BAT Catalog

We select 52 long gamma-ray bursts (GRBs) that have precursor activity in the third Swift-BAT catalog. Each episode shown in both the precursors and the main bursts is fitted by the Norris function. We systematically analyze the temporal properties for both the precursors and the main bursts. We do not find any significant difference between the temporal profile of the precursor and that of the main burst. The photon count of the precursor is related to that of the main burst. It is indicated that the precursor and the main burst might have the same physical origin, as the precursor and the main burst follow the same τ p -ω relation. However, we do not find the explicit relation between the energy release of the precursor and the quiescent time. Some theoretical models, such as the fallback collapsar scenario and the jet-cocoon scenario, may be helpful to explain the GRB-precursor phenomena.

Keywords: gamma-ray bursts
Enhanced Star Formation Activity of Extreme Jellyfish Galaxies in Massive Clusters and the Role of Ram Pressure Stripping

Jellyfish galaxies are an excellent tool to investigate the short-term effects of ram pressure stripping (RPS) on star formation in cluster environments. It has been thought that the star formation activity of jellyfish galaxies may depend on the host-cluster properties, but previous studies have not yet found a clear correlation. In this study, we estimate the Hα-based star formation rates (SFRs) of five jellyfish galaxies in massive clusters (σ v,cl ≳ 1000 km s-1) at z ~ 0.3-0.4 using Gemini GMOS/IFU observations to explore the relationship. Combining our results with those in the literature, we find that the star formation activity of jellyfish galaxies shows a positive correlation with their host-cluster velocity dispersion as a proxy of cluster mass and dynamical states. We divide the jellyfish galaxy sample into two groups with strong and weak RPS signatures using a morphological class. In the phase-space diagram, the jellyfish galaxies with strong RPS features show a higher SFR and a stronger central concentration than those with weak RPS features. We estimate their SFR excess relative to the star formation main sequence (starburstiness; R SB = SFR/SFRMS(z)) and the density of the surrounding intracluster medium (ICM) using scaling relations with the cluster velocity dispersion. As a result, the starburstiness of jellyfish galaxies with strong RPS signatures clearly exhibits positive correlations with cluster velocity dispersion, ICM density, and strength of ram pressure. This shows that the relation between RPS and star formation activity of jellyfish galaxies depends on the host-cluster properties and strength of the ram pressure.

Keywords: galaxy environments; galaxy clusters; ram pressure stripped tails; intracluster medium; starburst galaxies; galaxy spectroscopy
The NANOGrav 15 yr Data Set: Search for Anisotropy in the Gravitational-wave Background

The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) has reported evidence for the presence of an isotropic nanohertz gravitational-wave background (GWB) in its 15 yr data set. However, if the GWB is produced by a population of inspiraling supermassive black hole binary (SMBHB) systems, then the background is predicted to be anisotropic, depending on the distribution of these systems in the local Universe and the statistical properties of the SMBHB population. In this work, we search for anisotropy in the GWB using multiple methods and bases to describe the distribution of the GWB power on the sky. We do not find significant evidence of anisotropy. By modeling the angular power distribution as a sum over spherical harmonics (where the coefficients are not bound to always generate positive power everywhere), we find that the Bayesian 95% upper limit on the level of dipole anisotropy is (C l=1/C l=0) < 27%. This is similar to the upper limit derived under the constraint of positive power everywhere, indicating that the dipole may be close to the data-informed regime. By contrast, the constraints on anisotropy at higher spherical-harmonic multipoles are strongly prior dominated. We also derive conservative estimates on the anisotropy expected from a random distribution of SMBHB systems using astrophysical simulations conditioned on the isotropic GWB inferred in the 15 yr data set and show that this data set has sufficient sensitivity to probe a large fraction of the predicted level of anisotropy. We end by highlighting the opportunities and challenges in searching for anisotropy in pulsar timing array data.

Keywords: gravitational waves; gravitational wave astronomy; supermassive black holes; pulsars
Rapid Radical-Radical Induced Explosive Desorption of Ice-coated Interstellar Nanoparticles

The observation of complex organic molecules (COMs) in the gas phase of cold molecular clouds has coined a freeze-out paradox in astrophysics: COMs should be accreted on low-temperature interstellar grains, but not observable in cold molecular clouds. Still, validated mechanisms transporting molecules from the grains back into the gas phase are still elusive, but critical for our understanding of the chemical evolution of the molecular universe. Here we report on the first characterization of rapid radical reactions involving methyl (CH3) and formyl (HCO) radicals in interstellar analogous ices of methane (CH4) and carbon monoxide (CO) upon exposure to proxies of galactic cosmic rays. Rapid radical chain reactions and explosive desorption occurred once the accumulated radicals surpassed critical concentrations of about 1% in the ices at temperatures of cold molecular clouds (5-10 K). These processes may explain the ejection and observation of COMs in the gas phase of cold molecular clouds and potentially rapid outbursts of comets.

Keywords: laboratory astrophysics; interstellar molecules; radical-radical recombination; molecule formation; astrochemistry
Early Results from GLASS-JWST. XI. Stellar Masses and Mass-to-light Ratio of z > 7 Galaxies

We exploit James Webb Space Telescope (JWST) NIRCam observations from the GLASS-JWST-Early Release Science program to investigate galaxy stellar masses at z > 7. We first show that JWST observations reduce the uncertainties on the stellar mass by a factor of at least 5-10, when compared with the highest-quality data sets available to date. We then study the UV mass-to-light ratio, finding that galaxies exhibit a a two orders of magnitude range of M/L UV values for a given luminosity, indicative of a broad variety of physical conditions and star formation histories. As a consequence, previous estimates of the cosmic stellar-mass density-based on an average correlation between UV luminosity and stellar mass-can be biased by as much as a factor of ~6. Our first exploration demonstrates that JWST represents a new era in our understanding of stellar masses at z > 7 and, therefore, of the growth of galaxies prior to cosmic reionization.

Keywords: high-redshift galaxies; stellar masses; mass-to-light ratio
Evolution of Solar-type Activity: A Brief Study of Ca II Emission in Beta Hydri (G2 IV)

We present results about the decrease of stellar activity for stars like the Sun evolving toward the subgiant stage. Specifically, we examine two-component chromosphere models (acoustic and magnetic) for β Hydri (G2 IV) based on detailed time-dependent simulations while focusing on Ca II emission. We convey models for two different photospheric magnetic filling factors.

Keywords: stellar physics
Mass Production of 2021 KMTNet Microlensing Planets. I

We inaugurate a program of "mass production" of microlensing planets discovered in 2021 KMTNet data, with the aim of laying the basis for future statistical studies. While we ultimately plan to quickly publish all 2021 planets meeting some minimal criteria, the current sample of four was chosen simply on the basis of having low initial estimates of the planet-host mass ratio, q. It is therefore notable that two members of this sample suffer from a degeneracy in the normalized source radius ρ that arises from different morphologies of closely spaced caustics. All four planets (KMT-2021-BLG-1391, KMT-2021-BLG-1253, KMT-2021-BLG-1372, KMT-2021-BLG-0748) have well-characterized mass ratios, q, and therefore are suitable for mass-ratio frequency studies. Both of the ρ degeneracies can be resolved by future adaptive optics (AO) observations on 30 m class telescopes. We provide general guidance for such AO observations for all events in anticipation of the prospect that they will revolutionize the field of microlensing planets.

Keywords: gravitational microlensing
The In Situ Exploration of a Relict Ocean World: An Assessment of Potential Landing and Sampling Sites for a Future Mission to the Surface of Ceres

The Dawn orbiter's exploration of Ceres, the most water-rich body in the inner solar system after Earth, revealed the dwarf planet to be a relict ocean world of great interest to the astrobiology and ocean worlds communities. Evidence for an early global subsurface ocean is preserved in Ceres' surface minerals. While most of the subsurface ocean froze billions of years ago, its liquid (preserved in a deep brine reservoir) and solid remnants are responsible for spectacular surface features such as the faculae in the Occator crater, Ahuna Mons, and Haulani crater. Therefore, the next step in Ceres exploration is an in situ mission to the surface, with these three features being among the most scientifically compelling targets. Here we demonstrate the process of identifying potential landing/sampling sites. Using the highest resolution data obtained by Dawn (up to ∼5 m/pixel in Occator and up to ∼35 m/pixel elsewhere), we identify safe and scientifically compelling potential landing/sampling sites in these three regions. For future landing/sample return, higher spatial resolution data (a few decimeters per pixel to ∼1 m/pixel) than are currently available are needed to identify hazards on the scale of a ∼1-5 m lander. Such data could be obtained in an orbital reconnaissance phase prior to landing/sampling. Orbital reconnaissance, in combination with terrain relative navigation/hazard avoidance, and the ability to land within a ≦100 m diameter circle (>800,000 of which fit within Occator), makes it highly likely that safe and scientifically compelling landing/sampling sites could be reached by a future in situ mission.

Keywords: ceres; landers; asteroid belt; dwarf planets; orbiters
The Bipolar Magnetic Emergence in the Solar Polar Region

Due to projection effect and polarization sensitivity, it is still unknown whether the bipolar magnetic emergence (BME) exists in the solar polar region. In this study, combining the magnetic observations from the Helioseismic and Magnetic Imager and imaging observations of the 211 Å waveband from the Atmospheric Imaging Assembly, we try to identify and diagnose the BME. Considering the magnetic evolution and the corresponding intensity variation in the extreme ultraviolet waveband, we find definite events of the BMEs in the solar polar region. In total, we identify more than 300 BMEs in the solar polar region in the whole year from 2010 June to 2011 May. We find that whether on the southern or northern polar region, the leading polarity of the BMEs is almost half-positive and half-negative, and the BMEs' magnetic axes show random distribution in that direction. These results imply the possible existence of local dynamo in the solar polar region.

Keywords: solar magnetic fields; sunspots; solar activity; solar photosphere; solar dynamo
H2 Formation on Interstellar Grains and the Fate of Reaction Energy

Molecular hydrogen is the most abundant molecular species in the universe. While no doubts exist that it is mainly formed on the interstellar dust grain surfaces, many details of this process remain poorly known. In this work, we focus on the fate of the energy released by the H2 formation on the dust icy mantles: how it is partitioned between the substrate and the newly formed H2, a process that has a profound impact on the interstellar medium. We carried out state-of-the-art ab initio molecular dynamics simulations of H2 formation on periodic crystalline and amorphous ice surface models. Our calculations show that up to two-thirds of the energy liberated in the reaction (~300 kJ mol-1 ~3.1 eV) is absorbed by the ice in less than 1 ps. The remaining energy (~140 kJ mol-1 ~1.5 eV) is kept by the newly born H2. Since it is 10 times larger than the H2 binding energy on the ice, the new H2 molecule will eventually be released into the gas phase. The ice water molecules within ~4 Å from the reaction site acquire enough energy, between 3 and 14 kJ mol-1 (360-1560 K), to potentially liberate other frozen H2 and, perhaps, frozen CO molecules. If confirmed, the latter process would solve the long standing conundrum of the presence of gaseous CO in molecular clouds. Finally, the vibrational state of the newly formed H2 drops from highly excited states (ν = 6) to low (ν ≤ 2) vibrational levels in a timescale of the order of picoseconds.

Keywords: astrochemistry