adsabs/SciX_UAT_keywords huggingface dataset:
An Inward-moving and Asymmetric Velocity Wave Detected in LAMOST-Gaia

The phase space, as coded by kinematic parameters and chemical abundances, is crucial for understanding the formation of the Galactic disk. Using red giant stars from the Galactic thin disk with [Fe/H] > - 0.8 and low-α ratios identified in LAMOST-Gaia, we detect numerous ridges and undulations in the R-V ϕ diagram coded by median V R . Strikingly, the slope of these features changes from -22 km s-1 kpc-1 to -8 km s-1 kpc-1 at R ~ 11.5 kpc. Accordingly, the R g-V ϕ plane, also coded by median V R , reveals wave-like structures that propagate outwards in the inner disk but reverse direction and move inwards beyond R g = 11.5 kpc. The most prominent feature is the G1 group, distinguished by its wider spread and negative median V R at R g ~ 15 kpc, contrasting with the narrower G0 group that exhibits positive median V R at R g < 11.5 kpc. Furthermore, the [C/N] versus [Fe/H] relationship for the G1 group mirrors the opposite trend compared to the G0 group. Since [C/N] serves as a proxy for age, this contrasting behavior suggests an inverse age-metallicity relation for the G1 group. Comparison with the Sagittarius dwarf galaxy reveals that the G1 group possesses distinct [Mg/Fe] and [Al/Fe] ratios, yet its [C/N] versus [Fe/H] pattern is similar to that of the Sgr dwarf galaxy. Based on these observations, we proposed that the inward-moving and asymmetric velocity wave G1 might be linked to the minor merge of the Sagittarius galaxy.

Keywords: milky way disk; stellar kinematics; milky way evolution; milky way dynamics
The Astrobiological Copernican Weak and Strong Limits for Intelligent Life

We present a cosmic perspective on the search for life and examine the likely number of Communicating Extra-Terrestrial Intelligent (CETI) civilizations in our Galaxy by utilizing the latest astrophysical information. Our calculation involves Galactic star formation histories, metallicity distributions, and the likelihood of stars hosting Earth-like planets in their habitable zones, under specific assumptions which we describe as the Astrobiological Copernican Weak and Strong conditions. These assumptions are based on the one situation in which intelligent, communicative life is known to exist—on our own planet. This type of life has developed in a metal-rich environment and has taken roughly 5 Gyr to do so. We investigate the possible number of CETI civilizations based on different scenarios. At one extreme is the Weak Astrobiological Copernican scenario—such that a planet forms intelligent life sometime after 5 Gyr, but not earlier. The other is the Strong Astrobiological Copernican scenario in which life must form between 4.5 and 5.5 Gyr, as on Earth. In the Strong scenario (under the strictest set of assumptions), we find there should be at least ${36}_{-32}^{+175}$ civilizations within our Galaxy: this is a lower limit, based on the assumption that the average lifetime, L, of a communicating civilization is 100 yr (since we know that our own civilization has had radio communications for this time). If spread uniformly throughout the Galaxy this would imply that the nearest CETI is at most ${17,000}_{-10,000}^{+33,600}$ lt-yr away and most likely hosted by a low-mass M-dwarf star, likely far surpassing our ability to detect it for the foreseeable future, and making interstellar communication impossible. Furthermore, the likelihood that the host stars for this life are solar-type stars is extremely small and most would have to be M dwarfs, which may not be stable enough to host life over long timescales. We furthermore explore other scenarios and explain the likely number of CETI there are within the Galaxy based on variations of our assumptions.

Keywords: astrobiology; astrostatistics; milky way galaxy; metallicity; stellar abundances; star formation; habitable planets; exoplanet astronomy; exoplanets
Relativistic Description of Dense Matter Equation of State and Compatibility with Neutron Star Observables: A Bayesian Approach

The general behavior of the nuclear equation of state (EOS), relevant for the description of neutron stars (NSs), is studied within a Bayesian approach applied to a set of models based on a density-dependent relativistic mean-field description of nuclear matter. The EOS is subjected to a minimal number of constraints based on nuclear saturation properties and the low-density pure neutron matter EOS obtained from a precise next-to-next-to-next-to-leading order (N3LO) calculation in chiral effective field theory (χEFT). The posterior distributions of the model parameters obtained under these minimal constraints are employed to construct the distributions of various nuclear matter properties and NS properties such as radii, tidal deformabilities, central energy densities, speeds of sound, etc. We found that a 90% confidence interval for the allowed NS mass-radius relationship and tidal deformabilities is compatible with GW170817 and recent Neutron star Interior Composition ExploreR observations, without invoking the exotic degrees of freedom. A central speed of sound of the order of $\sqrt{2/3}$ c is obtained. The maximum NS mass allowed by the model is 2.5 M ⊙.

Keywords: neutron star cores; neutron stars; nuclear astrophysics; nuclear physics
A Comprehensive Study of Five Intermediate-age Pismis (2, 3, 7, 12, 15) Clusters Using Photometric and Astrometric Data from Gaia EDR3

Open clusters are groups of stars that form simultaneously; hence, these are excellent probes to test theories of star formation, stellar evolution, and dynamics in the Milky Way disk. We carry out a detailed photometric and kinematic study of five poorly studied intermediate-age open clusters, Pismis 2 (Pi 2), Pismis 3 (Pi 3), Pismis 7 (Pi 7), Pismis 12 (Pi 12), and Pismis 15 (Pi 15), using the Gaia EDR3 database. By estimating the membership probabilities of stars, we recognized 635, 1488, 535, 368, and 494 most probable members for these clusters by using proper-motion and parallax data taken from Gaia EDR3. The radial density profiles of cluster members provide cluster radii of 4.'5-6.'5 for these clusters. Their ages range from 0.9 to 2.5 Gyr, and distances range, using parallax, from 2.15 to 5.10 kpc. The overall mass function slopes for main-sequence stars are found as 0.27 ± 0.16 (for 1.0-1.6 M ⊙ stars), 0.86 ± 0.27 (for 1.0-2.1 M ⊙ stars), 1.08 ± 0.32 (for 1.0-2.2 M ⊙ stars), 0.89 ± 0.38 (for 1.0-2.2 M ⊙ stars), and 1.07 ± 0.28 (for 1.0-2.1 M ⊙ stars) for clusters Pi 2, Pi 3, Pi 7, Pi 12, and Pi 15. Our obtained values of slopes are flatter in comparison with Salpeter's value (x = 1.35) within uncertainty. The present study demonstrates that all these Pismis clusters are dynamically relaxed. We found that these objects follow a circular path around the Galactic center. We compute these clusters' apex coordinates (A, D) and other kinematic parameters.

Keywords: open star clusters; initial mass function; stellar dynamics; stellar kinematics; orbits; proper motions
Subarcsecond Mid-infrared View of Local Active Galactic Nuclei. IV. The L- and M-band Imaging Atlas

We present the largest currently existing subarcsecond 3-5 μm atlas of 119 local (z < 0.3) active galactic nuclei (AGNs). This atlas includes AGNs of five subtypes: 22 are Seyfert 1; five are intermediate Seyferts; 46 are Seyfert 2; 26 are low-ionization nuclear emission regions; and 20 are composites/starbursts. Each active galactic nucleus was observed with the Very Large Telescope Infrared Spectrometer and Array Camera (ISAAC) in the L and/or M bands between 2000 and 2013. We detected at 3σ confidence 92 sources in the L band and 83 sources in the M band. We separated the flux into unresolved nuclear flux and resolved the flux through two-Gaussian fitting. We report the nuclear flux, extended flux, apparent size, and position angle of each source, giving 3σ upper limits for sources that are undetected. Using Wide-field Infrared Survey Explorer (WISE) W1- and W2-band photometry we derived relations predicting the nuclear L and M fluxes for Sy1 and Sy2 AGNs based on their W1-W2 color and WISE fluxes. Lastly, we compare the measured mid-infrared colors to those predicted by dusty torus models SKIRTOR, CLUMPY, CAT3D, and CAT3D-WIND, finding the best agreement with the latter. We find that models including polar winds best reproduce the 3-5 μm colors, indicating that it is an important component of dusty torus models. We found that several AGNs are bluer than models predict. We discuss several explanations for this and find that it is most plausibly stellar light contamination within the ISAAC L-band nuclear fluxes. * This atlas makes use of European Southern Observatory (ESO) observing programs 65.P-0519, 67.B-0332, 70.B-0393, 71.B-0379, 71.B-0404, 072.B-0397, 074.B-0166, 085.B-0639, and 290.B-5133.

Keywords: active galactic nuclei; agn host galaxies; infrared photometry; infrared galaxies
The Ages of Galactic Bulge Stars with Realistic Uncertainties

Using modern isochrones with customized physics and carefully considered statistical techniques, we recompute the age distribution for a sample of 91 microlensed dwarfs in the Galactic bulge presented by Bensby et al. and do not produce an age distribution consistent with their results. In particular, our analysis finds that only 15 of 91 stars have ages younger than 7 Gyr, compared to their finding of 42 young stars in the same sample. While we do not find a constituency of very young stars, our results do suggest the presence of an ~8 Gyr population at the highest metallicities, thus contributing to the long-standing debate about the age-metallicity distribution of the Galactic bulge. We supplement this with attempts at independent age determinations from two sources of photometry, BDBS and Gaia, but find that the imprecision of photometric measurements prevents reliable age and age uncertainty determinations. Lastly, we present age uncertainties derived using a first-order consideration of global modeling uncertainties in addition to standard observational uncertainties. The theoretical uncertainties are based on the known variance of free parameters in the 1D stellar evolution models used to generate isochrones, and when included, result in age uncertainties of 2-5 Gyr for this spectroscopically well-constrained sample. These error bars, which are roughly twice as large as typical literature values, constitute realistic lower limits on the true age uncertainties.

Keywords: galactic bulge; stellar ages; stellar evolutionary models
Age of FGK Dwarfs Observed with LAMOST and GALAH: Considering the Oxygen Enhancement

Varying oxygen abundance could impact modeling-inferred ages. This work aims to estimate the ages of dwarfs considering observed oxygen abundance. To characterize 67,503 LAMOST and 4006 GALAH FGK-type dwarf stars, we construct a grid of stellar models, which take into account oxygen abundance as an independent model input. Compared with ages determined with commonly used α-enhanced models, we find a difference of ~9% on average when the observed oxygen abundance is considered. The age differences between the two types of models are correlated to [Fe/H] and [O/α], and they are relatively significant on stars with [Fe/H] ≲ -0.6 dex. Generally, varying 0.2 dex in [O/α] will alter the age estimates of metal-rich (-0.2 < [Fe/H] < 0.2) stars by ~10% and relatively metal-poor (-1 < [Fe/H] < -0.2) stars by ~15%. Of the low-O stars with [Fe/H] < 0.1 dex and [O/α] ~-0.2 dex, many have fractional age differences of ≥ 10% and even reach up to 27%. The fractional age difference of high-O stars with [O/α] ~0.4 dex reaches up to -33% to -42% at [Fe/H] ≲ -0.6 dex. We also analyze the chemical properties of these stars. We find a decreasing trend of [Fe/H] with ages from 7.5-9 Gyr to 5-6.5 Gyr for the stars from the LAMOST and GALAH. The [O/Fe] of these stars increases with decreasing age from 7.5-9 Gyr to 3-4 Gyr, indicating that the younger population is more O rich.

Keywords: stellar abundances; stellar ages; stellar kinematics; milky way disk; fundamental parameters of stars
The ALMA Spectroscopic Survey in the HUDF: A Search for [C II] Emitters at 6 ≤ z ≤ 8

The Atacama Large Millimeter/submillimeter Array (ALMA) Spectroscopic Survey in the Hubble Ultra Deep Field (ASPECS) Band 6 scan (212-272 GHz) covers potential [C II] emission in galaxies at 6 ≤ z ≤ 8 throughout a 2.9 arcmin2 area. By selecting on known Lyα emitters (LAEs) and photometric dropout galaxies in the field, we perform targeted searches down to a 5σ [C II] luminosity depth L[C II] ∼ 2.0 × 108 L⊙, corresponding roughly to star formation rates (SFRs) of 10-20 M⊙ yr-1 when applying a locally calibrated conversion for star-forming galaxies, yielding zero detections. While the majority of galaxies in this sample are characterized by lower SFRs, the resulting upper limits on [C II] luminosity in these sources are consistent with the current literature sample of targeted ALMA observations of z = 6-7 LAEs and Lyman-break galaxies (LBGs), as well as the locally calibrated relations between L[C II] and SFR—with the exception of a single [C II]-deficient, UV-luminous LBG. We also perform a blind search for [C II]-bright galaxies that may have been missed by optical selections, resulting in an upper limit on the cumulative number density of [C II] sources with L[C II] > 2.0 × 108 L⊙ (5σ) to be less than 1.8 × 10-4 Mpc-3 (90% confidence level). At this luminosity depth and volume coverage, we present an observed evolution of the [C II] luminosity function from z = 6-8 to z ∼ 0 by comparing the ASPECS measurement to literature results at lower redshift.

Keywords: high-redshift galaxies; interstellar medium
Baryonic Feedback Measurement From KV450 Cosmic Shear Analysis

While baryonic feedback is one of the most important astrophysical systematics that we need to address in order to achieve precision cosmology, few weak lensing studies have directly measured its impact on the matter power spectrum. We report measurement of the baryonic feedback parameter with the constraints on its lower and upper limits from cosmic shear. We use the public data from the Kilo-Degree Survey and the VISTA Kilo-Degree Infrared Galaxy Survey spanning 450 deg2. Estimating both cosmological and feedback parameters simultaneously, we obtain ${A}_{{\rm{b}}}={1.01}_{-0.85}^{+0.80}$ , which shows a consistency with the dark matter-only (DMO) case at the ∼1.2σ level and a tendency toward positive feedback; the Ab = 0 (0.81) value corresponds to the DMO (OWLS AGN) case. Despite this full constraint of the feedback parameter, our ${S}_{8}\,(\equiv {\sigma }_{8}\sqrt{{{\rm{\Omega }}}_{m}/0.3})$ measurement ( ${0.739}_{-0.035}^{+0.036}$ ) shifts by only ∼6% of the statistical error, compared to the previous measurement. When we assume the flat ΛCDM cosmology favored by the Nine-Year Wilkinson Microwave Anisotropy Probe (Planck) result, the feedback parameter is constrained to be ${A}_{{\rm{b}}}={1.21}_{-0.54}^{+0.61}$ ( ${1.60}_{-0.52}^{+0.53}$ ), which excludes the DMO case at the ∼2.2σ (∼3.1σ) level.

Keywords: cosmology; cosmological parameters from large-scale structure; gravitational lensing shear; weak gravitational lensing; large-scale structure of the universe; astrophysical processes; observational cosmology
Zero Metallicity with Zero CPU Hours: Masses of the First Stars on the Laptop

We develop an analytic model for the mass of the first stars forming in the centers of primordial gas clouds as a function of host halo mass, redshift, and degree of rotation. The model is based on the estimation of key timescales determining the following three processes: the collapse of the gas cloud, the accretion onto the protostellar core, and the radiative feedback of the protostellar core. The final stellar mass is determined by the total mass accreted until the radiative feedback halts the accretion. The analytic estimation, motivated by the result of the full numerical simulations, leads to algebraic expressions allowing an extremely fast execution. Despite its simplicity, the model reproduces the stellar mass scale and its parameter dependencies observed in state-of-the-art cosmological zoom-in simulations. This work clarifies the basic physical principles undergirding such numerical treatments and provides a path to efficiently calibrating numerical predictions against eventual observations of the first stars.

Keywords: population iii stars; cosmology; star formation
Characterizing the Spectral Structure of Weak Impulsive Narrowband Quiet Sun Emissions

Weak Impulsive Narrowband Quiet Sun Emissions (WINQSEs) are a newly discovered class of radio emission from the solar corona. These emissions are characterized by their extremely impulsive, narrowband, and ubiquitous nature. We have systematically been working on their detailed characterization, including their strengths, morphologies, temporal characteristics, energies, etc. This work is the next step in this series and focuses on the spectral nature of WINQSEs. Given that their strength is only a few percent of the background solar emission, we have adopted an extremely conservative approach to reliably identify WINQSES. Only a handful of WINQSEs meet all of our stringent criteria. Their flux densities lie in the 20-50 Jy range and they have compact morphologies. For the first time, we estimate their bandwidths and find them to be less than 700 kHz, consistent with expectations based on earlier observations. Interestingly, we also find similarities between the spectral nature of WINQSEs and the solar radio spikes. This is consistent with our hypothesis that the WINQSEs are the weaker cousins of the type III radio bursts and are likely to be the low-frequency radio counterparts of the nanoflares, originally hypothesized as a possible explanation for coronal heating.

Keywords: quiet solar corona; solar coronal heating; solar radio emission
Gauss-Bonnet Inflation after Planck2018

We study the primordial perturbations and reheating process in the models where the Gauss-Bonnet (GB) term is nonminimally coupled to the canonical and noncanonical (DBI and tachyon) scalar fields. We consider several potentials and GB coupling terms as power-law, dilaton-like, cosh-type, E-model, and T-model. To seek the observational viability of these models, we study the scalar perturbations numerically and compare the results with the Planck2018 TT, TE, EE+lowE+lensing+BK14+BAO joint data at 68% CL and 95% CL. We also study the tensor perturbations in confrontation with the Planck2018 TT, TE, EE+lowE+lensing+BK14+BAO+ LIGO, and Virgo2016 joint data at 68% CL and 95% CL. In this regard, we obtain some constraints on the GB coupling parameter β. Another important process in the early universe is the reheating phase after inflation, which is necessary to reheat the universe for subsequent evolution. In this regard, we study the reheating process in these models and find some expressions for the e-folds number and temperature during that era. Considering that from Planck TT, TE, EE+lowEB+lensing data and BICEP2/Keck Array 2014, based on the ΛCDM $+r+\tfrac{{{dn}}_{s}}{d\mathrm{ln}k}$ model, we have ns = 0.9658 ± 0.0038 and r < 0.072, we obtain some constraints on the e-folds number and temperature. From the values of the e-folds number and the effective equation of state and also the observationally viable value of the scalar spectral index, we explore the capability of the models in explaining the reheating phase.

Keywords: inflationary universe; observational cosmology; early universe
HyGAL: Characterizing the Galactic Interstellar Medium with Observations of Hydrides and Other Small Molecules. I. Survey Description and a First Look Toward W3(OH), W3 IRS5, and NGC 7538 IRS1

The HyGAL Stratospheric Observatory for Infrared Astronomy legacy program surveys six hydride molecules-ArH+, OH+, H2O+, SH, OH, and CH-and two atomic constituents-C+ and O-within the diffuse interstellar medium (ISM) by means of absorption-line spectroscopy toward 25 bright Galactic background continuum sources. This detailed spectroscopic study is designed to exploit the unique value of specific hydrides as tracers and probes of different phases of the ISM, as demonstrated by recent studies with the Herschel Space Observatory. The observations performed under the HyGAL program will allow us to address several questions related to the life cycle of molecular material in the ISM and the physical processes that impact the phase transition from atomic to molecular gas, such as: (1) What is the distribution function of the H2 fraction in the ISM? (2) How does the ionization rate due to low-energy cosmic rays vary within the Galaxy? (3) What is the nature of interstellar turbulence (e.g., typical shear or shock velocities), and what mechanisms lead to its dissipation? In this overview, we discuss the observing strategy, the synergies with ancillary and archival observations of other small molecules, and the data reduction and analysis schemes we adopted; and we present the first results obtained toward three of the survey targets, W3(OH), W3 IRS5, and NGC 7538 IRS1. Robust measurements of the column densities of these hydrides-obtained through widespread observations of absorption lines-help address the questions raised, and there is a very timely synergy between these observations and the development of theoretical models, particularly pertaining to the formation of H2 within the turbulent ISM. The provision of enhanced HyGAL data products will therefore serve as a legacy for future ISM studies.

Keywords: interstellar abundances; astrochemistry; diffuse interstellar bands; molecular spectroscopy; interstellar medium
Interpreting High-resolution Spectroscopy of Exoplanets using Cross-correlations and Supervised Machine Learning

We present a new method for performing atmospheric retrieval on ground-based, high-resolution data of exoplanets. Our method combines cross-correlation functions with a random forest, a supervised machine-learning technique, to overcome challenges associated with high-resolution data. A series of cross-correlation functions are concatenated to give a "CCF-sequence" for each model atmosphere, which reduces the dimensionality by a factor of ∼100. The random forest, trained on our grid of ∼65,000 models, provides a likelihood-free method of retrieval. The precomputed grid spans 31 values of both temperature and metallicity, and incorporates a realistic noise model. We apply our method to HARPS-N observations of the ultra-hot Jupiter KELT-9b and obtain a metallicity consistent with solar (logM = - 0.2 ± 0.2). Our retrieved transit chord temperature ( $T={6000}_{-200}^{+0} K) is unreliable as strong ion lines lie outside of the extent of the training set, which we interpret as being indicative of missing physics in our atmospheric model. We compare our method to traditional nested sampling, as well as other machine-learning techniques, such as Bayesian neural networks. We demonstrate that the likelihood-free aspect of the random forest makes it more robust than nested sampling to different error distributions, and that the Bayesian neural network we tested is unable to reproduce complex posteriors. We also address the claim in Cobb et al. 2019 that our random forest retrieval technique can be overconfident but incorrect. We show that this is an artifact of the training set, rather than of the machine-learning method, and that the posteriors agree with those obtained using nested sampling.

Keywords: exoplanet atmospheres