adsabs/SciX_UAT_keywords huggingface dataset:
A Mini-Neptune Orbiting the Metal-poor K Dwarf BD+29 2654

We report the discovery and Doppler mass measurement of a 7.4 days 2.3 R ⊕ mini-Neptune around a metal-poor K dwarf BD+29 2654 (TOI-2018). Based on a high-resolution Keck/HIRES spectrum, the Gaia parallax, and multiwavelength photometry from the UV to the mid-infrared, we found that the host star has ${T}_{\mathrm{eff}}={4174}_{-42}^{+34}$ K, $\mathrm{log}g={4.62}_{-0.03}^{+0.02}$ , [Fe/H] = - 0.58 ± 0.18, M * = 0.57 ± 0.02 M ⊙, and R * = 0.62 ± 0.01 R ⊙. Precise Doppler measurements with Keck/HIRES revealed a planetary mass of M p = 9.2 ± 2.1 M ⊕ for TOI-2018 b. TOI-2018 b has a mass and radius that are consistent with an Earthlike core, with a ~1%-by-mass hydrogen/helium envelope or an ice-rock mixture. The mass of TOI-2018 b is close to the threshold for runaway accretion and hence giant planet formation. Such a threshold is predicted to be around 10M ⊕ or lower for a low-metallicity (low-opacity) environment. If TOI-2018 b is a planetary core that failed to undergo runaway accretion, it may underline the reason why giant planets are rare around low-metallicity host stars (one possibility is their shorter disk lifetimes). With a K-band magnitude of 7.1, TOI-2018 b may be a suitable target for transmission spectroscopy with the James Webb Space Telescope. The system is also amenable to metastable Helium observation; the detection of a Helium exosphere would help distinguish between a H/He-enveloped planet and a water world.

Keywords: exoplanets; mini neptunes; ocean planets
Planetary Engulfment Prognosis within the ρ CrB System

Exoplanets have been detected around stars at various stages of their lives, ranging from young stars emerging from formation to the latter stages of evolution, including white dwarfs and neutron stars. Post-main-sequence stellar evolution can result in dramatic, and occasionally traumatic, alterations to the planetary system architecture, such as tidal disruption of planets and engulfment by the host star. The ρ CrB system is a particularly interesting case of advanced main-sequence evolution, due to the relative late age and brightness of the host star, its similarity to solar properties, and the harboring of four known planets. Here, we use stellar evolution models to estimate the expected trajectory of the stellar properties of ρ CrB, especially over the coming 1.0-1.5 billion yr as it evolves off the main sequence. We show that the inner three planets (e, b, and c) are engulfed during the red giant phase and asymptotic giant branch, likely destroying those planets via either evaporation or tidal disruption at the fluid-body Roche limit. The outer planet, planet d, is briefly engulfed by the star several times toward the end of the asymptotic giant branch, but the stellar mass loss and subsequent changing planetary orbit may allow the survival of the planet into the white dwarf phase of the stellar evolution. We discuss the implications of this outcome for similar systems and describe the consequences for planets that may lie within the habitable zone of the system.

Keywords: exoplanets; astrobiology; habitable zone; stellar evolution; stellar evolutionary models; expanding stellar envelopes; red giant branch
AGN Sub-populations Important for Black Hole Mass Growth: A Rule of Thumb

For building the super-massive black hole population within a Hubble time, only sub-populations with more than ${10}^{52}\,\mathrm{erg}\,{{\rm{s}}}^{-1}/\overline{L}$ objects on the sky are relevant, where $\overline{L}$ is the sample-averaged bolometric luminosity.

Keywords: black holes; active galactic nuclei; galaxy evolution; surveys
Simple Convective Accretion Flows (SCAFs): Explaining the ≈ -1 Density Scaling of Hot Accretion Flows around Compact Accretors

Recent simulations find that hot gas accretion onto compact accretors is often highly turbulent and diskless, and shows a power-law density profile with slope α ρ ≈ -1. These results are consistent with observational constraints, but do not match existing self-similar solutions of radiatively inefficient accretion flows. We develop a theory for this new class of accretion flows, which we dub simple convective accretion flows (SCAFs). We use a set of hydrodynamic simulations to provide a minimalistic example of SCAFs, and develop an analytic theory to explain and predict key flow properties. We demonstrate that the turbulence in the flow is driven locally by convection, and argue that radial momentum balance, together with an approximate up-down symmetry of convective turbulence, yields α ρ = -1 ± few 0.1. Empirically, for an adiabatic hydrodynamic flow with γ ≈ 5/3, we get α ρ ≈ -0.8; the resulting accretion rate (relative to the Bondi accretion rate), $\dot{M}/{\dot{M}}_{{\rm{B}}}\sim {({r}_{\mathrm{acc}}/{r}_{{\rm{B}}})}^{0.7}$ , agrees very well with the observed accretion rates in Sgr A*, M87*, and a number of wind-fed supergiant X-ray binaries. We also argue that the properties of SCAFs are relatively insensitive to additional physical ingredients such as cooling and magnetic field; this explains their common appearance across simulations of different astrophysical systems.

Keywords: accretion; compact objects; hydrodynamical simulations
Nonuniversal Interstellar Density Spectra Probed by Pulsars

Galactic interstellar turbulence affects density distribution and star formation. We introduce a new method of measuring interstellar turbulent density spectra by using the dispersion measures (DMs) of a large sample of pulsars. Without the need of invoking multiple tracers, we obtain nonuniversal density spectra in the multiphase interstellar medium over different ranges of length scales. By comparing the analytical structure function of DMs with the observationally measured one in different areas of sky, we find a shallow density spectrum arising from the supersonic turbulence in cold interstellar phases, and a Kolmogorov-like density spectrum in the diffuse warm ionized medium (WIM). Both spectra extend up to hundreds of parsecs. On larger scales, we identify, for the first time, a steep density spectrum in the diffuse WIM extending up to several kiloparsecs. Our results show that the DMs of pulsars can provide unique new information on the interstellar turbulence.

Keywords: radio pulsars; interstellar medium; hydrodynamics; theoretical techniques
ALMA Confirmation of Millimeter Time Variability in the Gamma-Ray Detected Seyfert Galaxy GRS 1734-292

GRS 1734-292 is a radio-quiet galaxy, exhibiting neither intense starburst nor jet activities. However, Fermi-LAT detected this object in the GeV band. The origin of nonthermal activity in this Seyfert galaxy is an intriguing question. We report Atacama Large Millimeter/submillimeter Array observations of GRS 1734-292 at frequencies of 97.5, 145, and 225 GHz. These observations confirmed the millimeter excess within the central ⪅100 pc region and its time variability based on two separate observations conducted 4 days apart. The timescale of variability aligns with the light-crossing time for a compact source smaller than <100 Schwarzschild radius. If we take into account the power-law synchrotron emission originating from the corona (i.e., the hot plasma located above the accretion disk), the millimeter spectrum indicates the coronal magnetic field of ≈10 G and the size of ≈10 Schwarzschild radius. An alternative explanation for this millimeter emission could be synchrotron and free–free emission from disk winds (i.e., fast wide-opening angle outflows from the disk) with the size of ≈10 pc, although it may be difficult to explain the fast variability. Future millimeter observations with higher resolution (<0.″01) will enable the differentiation between these two scenarios. Such observations will provide insights into the acceleration sites of high-energy particles at the core of active galactic nuclei.

Keywords: astrophysical black holes; black hole physics; black holes; supermassive black holes; active galactic nuclei; seyfert galaxies; particle astrophysics; high energy astrophysics
Infrared Excesses around Bright White Dwarfs from Gaia and unWISE. I.

Studies of excess infrared radiation around white dwarfs provide important constraints on the evolution of planetary systems and low-mass companions beyond the main-sequence stage. In this paper series, we focus on identifying and characterizing bright white dwarfs with an infrared excess. Here, we present 188 infrared excess candidates from Gaia and unWISE, 147 of which are new discoveries. Further characterization of this sample can significantly increase the current list of white dwarf debris disks and white dwarfs with low-mass companions.

Keywords: circumstellar disks; white dwarf stars; brown dwarfs
Under Einstein's Microscope: Measuring Properties of Individual Rotating Massive Stars from Extragalactic Microcaustic Crossings

Highly magnified stars residing in caustic crossing lensed galaxies at z ≃ 0.7–1.5 in galaxy cluster lensing fields inevitably exhibit recurrent brightening events as they traverse a microcaustic network cast down by foreground intracluster stars. The detectable ones belong to nature's most massive and luminous class of stars, with evolved blue supergiants being the brightest ones at optical wavelengths. Considering single stars in this work, we study to what extent intrinsic stellar parameters are measurable from multifilter light curves, which can be obtained with optical/near-IR space telescopes during one or multiple caustic crossing events. We adopt a realistic model for the axisymmetric surface brightness profiles of rotating O/B stars and develop a numerical lensing code that treats finite source size effects. With a single microcaustic crossing, the ratio of the surface rotation velocity to the breakup value is measurable to a precision of ∼0.1–0.2 for feasible observation parameters with current space telescopes, with all unknown intrinsic and extrinsic parameters marginalized over and without a degeneracy with inclination. Equatorial radius and bolometric luminosity can be measured to 1/3 and 2/3 of the fractional uncertainty in the microcaustic strength, for which the value is not known at each crossing but an informative prior can be obtained from theory. Parameter inference precision may be further improved if multiple caustic crossing events for the same lensed star are jointly analyzed. Our results imply new opportunities to survey individual massive stars in star formation sites at z ≃ 0.7–1.5 or beyond.

Keywords: strong gravitational lensing; fundamental parameters of stars; stellar rotation; gravitational microlensing
Rapid Localization of Gravitational Wave Sources from Compact Binary Coalescences Using Deep Learning

The mergers of neutron star-neutron star and neutron star-black hole binaries (NSBHs) are the most promising gravitational wave (GW) events with electromagnetic (EM) counterparts. The rapid detection, localization, and simultaneous multimessenger follow-up of these sources are of primary importance in the upcoming science runs of the LIGO-Virgo-KAGRA Collaboration. While prompt EM counterparts during binary mergers can last less than 2 s, the timescales of existing localization methods that use Bayesian techniques, vary from seconds to days. In this paper, we propose the first deep learning-based approach for rapid and accurate sky localization of all types of binary coalescences, including neutron star-neutron star and NSBHs for the first time. Specifically, we train and test a normalizing flow model on matched-filtering output from GW searches to obtain sky direction posteriors in around 1 s using a single P100 GPU, which is several orders of magnitude faster than full Bayesian techniques.

Keywords: gravitational waves; gravitational wave sources; convolutional neural networks; neural networks
Algorithmic Speedups and Posterior Biases from Orbit Fitting of Directly Imaged Exoplanets in Cartesian Coordinates

A planet's orbit encodes information about its formation and history. However, exoplanets detected via direct-imaging are often only observed over a small fraction of their periods. Several problems arise from such unconstraining data, like slow convergence of standard orbit-fitting algorithms and significant biases in the estimation of orbital parameters. One possible way of overcoming some of these problems is performing orbit-fits in orbital bases distinct from the usual Keplerian elements. We explore this approach by fitting orbits in Cartesian coordinates, that is, estimating the position and velocity vectors for a planet at a given epoch. We saw a significant improvement in the MCMC convergence time compared to the Keplerian elements, and different posterior shapes were observed with different priors. In particular, setting Gaussian priors in the line-of-sight components (z and $\dot{z}$ ) produced posteriors more similar to the ones obtained via the Keplerian basis compared to uniform priors on them.

Keywords: exoplanets; exoplanet astronomy; direct imaging; exoplanet detection methods; bayesian statistics; posterior distribution; markov chain monte carlo; affine invariant
Dark Dragon Breaks Magnetic Chain: Dynamical Substructures of IRDC G28.34 Form in Supported Environments

We have comprehensively studied the multiscale physical properties of the massive infrared dark cloud G28.34 (the Dragon cloud) with dust polarization and molecular line data from Planck, FCRAO-14 m, James Clerk Maxwell Telescope, and Atacama Large Millimeter/submillimeter Array. We find that the averaged magnetic fields of clumps tend to be either parallel with or perpendicular to the cloud-scale magnetic fields, while the cores in clump MM4 tend to have magnetic fields aligned with the clump fields. Implementing the relative orientation analysis (for magnetic fields, column density gradients, and local gravity), velocity gradient technique, and modified Davis–Chandrasekhar–Fermi analysis, we find that G28.34 is located in a trans-to-sub-Alfvénic environment; the magnetic field is effectively resisting gravitational collapse in large-scale diffuse gas, but is distorted by gravity within the cloud and affected by star formation activities in high-density regions, and the normalized mass-to-flux ratio tends to increase with increasing density and decreasing radius. Considering the thermal, magnetic, and turbulent supports, we find that the environmental gas of G28.34 is in a supervirial (supported) state, the infrared dark clumps may be in a near-equilibrium state, and core MM4-core4 is in a subvirial (gravity-dominant) state. In summary, we suggest that magnetic fields dominate gravity and turbulence in the cloud environment at large scales, resulting in relatively slow cloud formation and evolution processes. Within the cloud, gravity could overwhelm both magnetic fields and turbulence, allowing local dynamical star formation to happen.

Keywords: star formation; molecular clouds; interstellar medium; magnetic fields
Detection of H2 in the TWA 7 System: A Probable Circumstellar Origin

Using HST-COS far-UV spectra, we have discovered warm molecular hydrogen in the TWA 7 system. TWA 7, a ~9 Myr old M2.5 star, has a cold debris disk and has previously shown no signs of accretion. Molecular hydrogen is expected to be extremely rare in a debris disk. While molecular hydrogen can be produced in starspots or the lower chromospheres of cool stars such as TWA 7, fluxes from progressions that get pumped by the wings of Lyα indicate that this molecular hydrogen could be circumstellar and thus that TWA 7 is accreting at very low levels and may retain a reservoir of gas in the near circumstellar environment.

Keywords: protoplanetary disks; debris disks; t tauri stars; planet formation; high resolution spectroscopy; ultraviolet astronomy; circumstellar gas
Narrowband Ca Photometry for Dwarf Spheroidal Galaxies. I. Chemostructural Study on Draco, Sextans, and Canes Venatici I

A few dozen dwarf satellite galaxies of the Milky Way have been discovered, which are often viewed as the remaining building blocks of our Galaxy. The follow-up spectroscopy showed that dwarf galaxies have a sizeable spread in their metallicities. Several scenarios were suggested to explain the metallicity spread, which can be tested by the structural patterns of stellar subpopulations with distinct metallicities. However, such chemical plus structural examination, which we refer to as "chemostructural study," is hindered by the lack of stars with spectroscopic metallicity. Here we propose the Ca-by photometry as an alternative way to secure metallicities for a 2-3 orders of magnitude larger stellar sample than the spectroscopic sample and thus enable us to perform a chemostructural study on dwarf galaxies. In particular, we use the hk index [≅(Ca - b) - (b - y)], whose validity as a photometric metallicity indicator (and crass insensitivity to age) for red-giant-branch stars was upheld via Galactic globular clusters, and observe three dwarf spheroidal galaxies - Draco, Sextans, and Canes Venatici I (CVnI) - with Subaru/Suprime-Cam. We find that in all the galaxies the metal-rich stellar populations are more centrally concentrated than the metal-poor counterparts, suggesting that the central regions of the galaxies underwent extended star formation. Such a negative radial metallicity gradient for Sextans and CVnI opposes the traditional spectroscopic results. We also find that their metallicity distribution functions (MDFs) can be characterized by a unimodal, skewed Gaussian shape with a metal-rich peak and a metal-poor tail. We discuss their features in the chemo-structure and MDF in terms of dwarf galaxy formation theories.

Keywords: local group; dwarf spheroidal galaxies; galaxy stellar content; galaxy structure; stellar abundances
New Constraint on the Tensor-to-scalar Ratio from the Planck and BICEP/Keck Array Data Using the Profile Likelihood

Motivated by the discrepancy between Bayesian and frequentist upper limits on the tensor-to-scalar ratio parameter r found by the SPIDER collaboration, we investigate whether a similar trend is also present in the latest Planck and BICEP/Keck Array data. We derive a new upper bound on r using the frequentist profile likelihood method. We vary all the relevant cosmological parameters of the ΛCDM model, as well as the nuisance parameters. Unlike the Bayesian analysis using Markov Chain Monte Carlo (MCMC), our analysis is independent of the choice of priors. Using Planck Public Release 4, BICEP/Keck Array 2018, Planck cosmic microwave background lensing, and baryon acoustic oscillation data, we find an upper limit of r < 0.037 at 95% Confidence Level (C.L.), similar to the Bayesian MCMC result of r < 0.038 for a flat prior on r and a conditioned Planck lowlEB covariance matrix.

Keywords: cosmic microwave background radiation; cosmic inflation; cosmology; cosmological parameters
Investigating Diurnal and Seasonal Turbulence Variations of the Martian Atmosphere Using a Spectral Approach

We use a spectral approach to analyze the pressure and wind data from the InSight mission and investigate the diurnal and seasonal trends. Our analyses show that the daytime pressure and wind spectra have slopes of approximately -1.7 and -1.3 and, therefore, do not follow the Kolmogorov scaling (as was also previously reported for a reduced data set in Banfield et al.). We find that the nighttime pressure spectral slope is close to -1 (as reported in Temel et al.), and that the wind speed spectral slope is close to -0.5, flatter than the theoretical slope expected for the shear-dominated regime. We observe strong nocturnal (likely shear-generated) turbulent behavior starting around L s = 150° (InSight sol 440) that shifts to progressively earlier local times before reaching the "5th season" (InSight sols 530-710) identified by Chatain et al.. The diurnal spectral slope analyses indicate an asymmetry in the diurnal behavior of the Martian boundary layer, with a slow growth and fast collapse mechanism. Finally, the low-frequency (5-30 mHz) pressure data exhibit large spectral slope oscillations. These occur particularly during the periods with a highly stable atmosphere and, therefore, may be linked to gravity wave activity.

Keywords: atmospheric dynamics; mars
Tidal Distortions as a Bottleneck on Constraining Exoplanet Compositions

Improvements in the number of confirmed planets and the precision of observations imply a need to better understand subtle effects that may bias interpretations of exoplanet observations. One such effect is the distortion of a short period planet by its host star, affecting its derived density. We extend the work of Burton et al., Correia, and others, using a gravitational potential formulation to a sample of nearly 200 planets with periods less than 3 days. We find five planets exhibiting density variations of >10% and as many as 20 planets with deviations >5%. We derive an analytic approximation for this deviation as a function of the orbital period, transit depth, and mass ratio between the planet and host star, allowing for rapid determination of such tidal effects. We find that current density error bars are typically larger than tidal deviations but that reducing the uncertainty on transit depth and radial velocity (RV) amplitude by a factor of 3 causes tidal effects to dominate density errors (>50%) in >40% of planets in our sample, implying that in the near future upgraded observational precision will cause shape deviations to become a bottleneck with regards to analysis of exoplanet compositions. These two parameters are found to dominate uncertainties compared to errors on stellar mass and radius. We identify a group of eight planets (including WASP-19 b, HAT-P-7 b, and WASP-12 b) for which current density uncertainties are as much as 4× smaller than the potential shift due to tides, implying a possible 4σ bias on their density estimates.

Keywords: exoplanets; exoplanet astronomy; exoplanet structure; tidal distortion
Robust Estimates of Orientation between Astrometric Catalogs

Accurately comparing two celestial reference frames based on the observed position of a number of common objects requires to detect and appropriately process outliers, lest they spuriously influence the results. It is thus of practical importance to use algorithms able to minimize the impact of those outliers when comparing radio and/or optical astrometric catalogs. In this paper, we investigate and compare the performances of some well-established and more recent robust algorithms when fitting a simple rotation vector between two reference frames. We particularly focus on two aspects: the variance of the resulting estimates, and the ability of the estimators to deal with outlying leverage points. We ran a number of Monte Carlo simulations with synthetic objects, varying their number, as well as the fraction and dispersion of outliers. Since the distribution of catalog objects in the sky is sometimes markedly nonuniform as in the case of the ICRF3 catalog, and because the position of outliers in the sky might cause issues when fitting rotation models, we also ran simulations representative of the observed distribution of objects. We compare the ICRF3 S/X, ICRF2 and Gaia EDR3 reference frames. Our results, based on the synthetic simulations and the comparison between the existing celestial frames, show that the M estimator, with a scale obtained from a least absolute deviations estimate, is the best among all the robust estimators compared.

Keywords: astrometry; astrostatistics techniques; robust regression