adsabs/SciX_UAT_keywords huggingface dataset:
Spatially Resolved Observations of Betelgeuse at λ7 mm and λ1.3 cm Just prior to the Great Dimming

We present spatially resolved observations of Betelgeuse (α Orionis) obtained with the Karl G. Jansky Very Large Array at λ ~ 7 mm (44 GHz) and λ ~ 1.3 cm (22 GHz) on 2019 August 2, just prior to the onset of the historical optical dimming that occurred between late 2019 and early 2020. Our measurements suggest recent changes in the temperature and density structure of the atmosphere between radii r ~ 2R⋆ and 3R⋆. At λ7 mm the star is ~20% dimmer than in previously published observing epochs between 1996 and 2004. We measure a mean gas temperature of T B = 2270 ± 260 K at r ~ 2.1R⋆, where R ⋆ is the canonical photospheric radius. This is ~2σ lower than previously reported temperatures at comparable radii and >1200 K lower than predicted by previous semiempirical models of the atmosphere. The measured brightness temperature at r ~ 2.6R ⋆ (T B = 2580 ± 260 K) is also cooler than expected based on trends in past measurements. The stellar brightness profile in our current measurements appears relatively smooth and symmetric, with no obvious signatures of giant convective cells or other surface features. However, the azimuthally averaged brightness profile is found to be more complex than a uniform elliptical disk. Our observations were obtained approximately 6 weeks before spectroscopic measurements in the ultraviolet revealed evidence of increases in the chromospheric electron density in the southern hemisphere of Betelgeuse, coupled with a large-scale outflow. We discuss possible scenarios linking these events with the observed radio properties of the star, including the passage of a strong shock wave.

Keywords: red supergiant stars; pulsating variable stars; stellar physics; stellar properties; stellar chromospheres; aperture synthesis; radio interferometry; stellar surfaces
Improved Measurements of Galaxy Star Formation Stochasticity from the Intrinsic Scatter of Burst Indicators

Measurements of short-timescale star formation variations (i.e., "burstiness" or star formation stochasticity) are integral to our understanding of star formation feedback mechanisms and the assembly of stellar populations in galaxies. We expand upon the work of Broussard et al. by introducing a new analysis of galaxy star formation burstiness that accounts for variations in the ${Q}_{{sg}}=E{\left(B-V\right)}_{\mathrm{stars}}/E{\left(B-V\right)}_{\mathrm{gas}}$ distribution, a major confounding factor. We use Balmer decrements from the MOSFIRE Deep Evolution Field (MOSDEF) survey to measure Q sg , which we use to construct mock catalogs from the Santa Cruz Semi-Analytic Models and MUFASA cosmological hydrodynamical simulation based on 3D-HST, Fiber Multi-Object Spectrograph (FMOS)-COSMOS, and MOSDEF galaxies with Hα detections. The results of the mock catalogs are compared against observations using the burst indicator $\eta ={\mathrm{log}}_{10}({\mathrm{SFR}}_{{\rm{H}}\alpha }/{\mathrm{SFR}}_{\mathrm{NUV}})$ , with the standard deviation of the η distribution indicating burstiness. We find decent agreement between mock and observed η distribution shapes; however, the FMOS-COSMOS and MOSDEF mocks show a systematically low median and scatter in η in comparison to the observations. This work also presents the novel approach of analytically deriving the relationship between the intrinsic scatter in η, scatter added by measurement uncertainties, and observed scatter, resulting in an intrinsic burstiness measurement of 0.06-0.16 dex.

Keywords: galaxy evolution; star formation; starburst galaxies
Evolutionary Status of Selected Post-AGB Single and Binary Stars in Gaia DR3

Gaia data is helping to further understand the evolutionary status of post-AGB and related stars. In this paper we present an analysis of Gaia DR3 data of post-AGB stars and post-AGB binaries with accurate parallaxes. Gaia DR3 data of 44 post-AGB candidates are analyzed, including 16 post-AGB binary candidates. Of these, 19 stars have RUWE values >1.4. For several stars, the calculated absolute luminosities confirm that they are indeed in post-AGB evolutionary stage. We find that 12 stars have relatively lower luminosities; some of them may be post-RGB stars and some may be post-HB stars. We find that IRAS 01427+4633 (BD+46 442), IRAS 16230-3410, and IRAS 19199+3950 (HP Lyr) are evolved high velocity stars.

Keywords: post-asymptotic giant branch stars; binary stars; stellar distance; stellar evolution
Plasma Oscillations and Kinetic Instabilities at Ion Scales in the Expanding Magnetosheath

We investigate a relationship between a decaying spectrum of magnetic field perturbations and kinetic instabilities in a slowly expanding magnetosheath plasma using two-dimensional hybrid expanding simulations in (X, Y) space. We impose an initial ambient magnetic field B 0/B 0 = (1, 0, 0), and superimpose a flat spectrum of Alfvénic fluctuations with average amplitudes equal to δ B = ∣B - B 0∣ ~ 0.2B 0. The expansion leads to the development of temperature anisotropy A p = T p⊥/T p∥ > 1 (T p⊥, T p∥ are plasma temperatures perpendicular and parallel with respect to B 0, respectively) and the system becomes unstable with respect to the ion cyclotron and mirror instabilities. The onset of mirror instability in the early stage of the simulation leads to the development of filaments that fill the simulation volume. The filaments represent pressure-balanced structures as they develop in the form of magnetic field (δ B) perturbations balanced with corresponding density perturbations. Further expansion of the system leads to the thinning of these filaments, which gradually become extremely narrow. The filamentation maintains the power spectral density in δ B ⊥ at ${P}_{{{\boldsymbol{B}}}_{\perp }}\sim {10}^{-3}{B}_{0}^{2}{d}_{p0}$ (here d p0 is the proton inertial length) over the range 0.2 < kd p0 < 1.1. The filaments remain well developed in the form of density, magnetic field, and temperature anisotropy perturbations at t ~ 10,000/Ω p0 (here Ω p0 is the initial proton gyrofrequency) and slowly dissipate when the expansion continues further.

Keywords: earth (planet); planetary magnetospheres
The Launching of Cold Clouds by Galaxy Outflows. V. The Role of Anisotropic Thermal Conduction

Motivated by observations of multiphase galaxy outflows, we explore the impact of isotropic and anisotropic electron thermal conduction on the evolution of radiatively cooled, cold clouds embedded in hot, magnetized winds. Using the adaptive-mesh refinement code ATHENAPK, we conduct simulations of clouds impacted by supersonic and transonic flows with magnetic fields initially aligned parallel and perpendicular to the flow direction. In cases with isotropic thermal conduction, an evaporative wind forms, stabilizing against instabilities and leading to a mass-loss rate that matches the hydrodynamic case. In anisotropic cases, the impact of conduction is more limited and strongly dependent on the field orientation. In runs with initially perpendicular fields, the field lines are folded back into the tail, strongly limiting conduction, but magnetic fields act to dampen instabilities and slow the stretching of the cloud in the flow direction. In the parallel case, anisotropic conduction aids cloud survival by forming a radiative wind near the front of the cloud, which suppresses instabilities and reduces mass loss. In all cases, anisotropic conduction has a minimal impact on the acceleration of the cloud.

Keywords: circumgalactic medium
Cosmological Parameter Estimation from the Two-dimensional Genus Topology: Measuring the Shape of the Matter Power Spectrum

We present measurements of the two-dimensional genus of the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS) catalogs to constrain cosmological parameters governing the shape of the matter power spectrum. The BOSS data are divided into 12 concentric shells over the redshift range 0.2 < z < 0.6, and we extract the genus from the projected two-dimensional galaxy density fields. We compare the genus amplitudes to their Gaussian expectation values, exploiting the fact that this quantity is relatively insensitive to nonlinear gravitational collapse. The genus amplitude provides a measure of the shape of the linear matter power spectrum and is principally sensitive to Ωch2 and scalar spectral index ns. A strong negative degeneracy between Ωch2 and ns is observed, as both can increase small-scale power by shifting the peak and tilting the power spectrum, respectively. We place a constraint on the particular combination ${n}_{{\rm{s}}}^{3/2}{{\rm{\Omega }}}_{{\rm{c}}}{h}^{2}$ —we find ${n}_{{\rm{s}}}^{3/2}{{\rm{\Omega }}}_{{\rm{c}}}{h}^{2}=0.1121\pm 0.0043$ after combining the LOWZ and CMASS data sets, assuming a flat ΛCDM cosmology. This result is practically insensitive to reasonable variations of the power spectrum amplitude and linear galaxy bias. Our results are consistent with the Planck best fit ${n}_{{\rm{s}}}^{3/2}{{\rm{\Omega }}}_{{\rm{c}}}{h}^{2}=0.1139\pm 0.0009$ .

Keywords: large-scale structure of the universe; cosmological parameters from large-scale structure; observational cosmology
Bayesian Cross-matching of High Proper-motion Stars in Gaia DR2 and Photometric Metallicities for 1.7 million K and M Dwarfs

We present a Bayesian method to cross-match 5,827,988 high proper-motion Gaia sources ( > 40 mas yr1) to various photometric surveys: Two Micron All Sky Survey, AllWISE data release from the Wide-field Infrared Explorer (WISE) mission, Galaxy Evolution Explorer, Radial Velocity Experiment, Sloan Digital Sky Survey, and Panoramic Survey Telescope and Rapid Response System (Pan-STARRS). To efficiently associate these objects across catalogs, we develop a technique that compares the multidimensional distribution of all sources in the vicinity of each Gaia star to a reference distribution of random field stars obtained by extracting all sources in a region on the sky displaced 2. This offset preserves the local field stellar density and magnitude distribution, allowing us to characterize the frequency of chance alignments. The resulting catalog with Bayesian probabilities >95 has a marginally higher match rate than current internal Gaia data release 2 (DR2) matches for most catalogs. However, a significant improvement is found with Pan-STARRS, where 99.8 of the sample within the Pan-STARRS footprint is recovered, as compared to a low 20.8 in Gaia DR2. Using these results, we train a Gaussian process regressor to calibrate two photometric metallicity relationships. For dwarfs of 3500 < Teff < 5280 K, we use metallicity values of 4378 stars from the Apache Point Observatory Galactic Evolution Experiment and Hejazi et al. to calibrate the relationship, producing results with a 1 precision of 0.12 dex and few systematic errors. We then indirectly infer the metallicity of 4018 stars with 2850 < Teff < 3500 K, which are wide companions of primaries whose metallicities are estimated with our first regressor, to produce a relationship with a 1 precision of 0.21 dex and significant systematic errors. Additional work is needed to better remove unresolved binaries from this second sample to reduce these systematic errors.

Keywords: catalogs; sky surveys; astrometry; chemical abundances
Water and an Escaping Helium Tail Detected in the Hazy and Methane-depleted Atmosphere of HAT-P-18b from JWST NIRISS/SOSS

JWST is here. The early release observation (ERO) program provides us with the first look at the scientific data and the spectral capabilities. One of the targets from the ERO is HAT-P-18b, an inflated Saturn-mass planet with an equilibrium temperature of ~850 K. We present the NIRISS/SOSS transmission spectrum of HAT-P-18b from 0.6 to 2.8 μm and reveal the planet in the infrared beyond 1.6 μm for the first time. From the spectrum, we see clear water and escaping helium tail features in an otherwise very hazy atmosphere. Our free chemistry retrievals with ATMO show moderate Bayesian evidence (3.79) supporting the presence of methane, but the spectrum does not display any clearly identifiable methane absorption features. The retrieved methane abundance is ~2 orders of magnitude lower than that of solar composition. The methane-depleted atmosphere strongly rejects simple equilibrium chemistry forward models with solar metallicity and a C/O ratio and disfavors high metallicity (100 times) and a low C/O ratio (0.3). This calls for additional physical processes such as vertical mixing and photochemistry, which can remove methane from the atmosphere.

Keywords: exoplanet atmospheres; exoplanet atmospheric composition; exoplanet astronomy
Relic Gravitational Waves from the Chiral Magnetic Effect

Relic gravitational waves (GWs) can be produced by primordial magnetic fields. However, not much is known about the resulting GW amplitudes and their dependence on the details of the generation mechanism. Here we treat magnetic field generation through the chiral magnetic effect (CME) as a generic mechanism and explore its dependence on the speed of generation (the product of magnetic diffusivity and characteristic wavenumber) and the speed characterizing the maximum magnetic field strength expected from the CME. When the latter exceeds the former (regime I), which is the regime applicable to the early universe, we obtain an inverse cascade with moderate GW energy that scales with the third power of the magnetic energy. When the generation speed exceeds the CME limit (regime II), the GW energy continues to increase without a corresponding increase of magnetic energy. In the early kinematic phase, the GW energy spectrum (per linear wavenumber interval) has opposite slopes in both regimes and is characterized by an inertial range spectrum in regime I and a white noise spectrum in regime II. The occurrence of these two slopes is shown to be a generic consequence of a nearly monochromatic exponential growth of the magnetic field. The resulting GW energy is found to be proportional to the fifth power of the limiting CME speed and the first power of the generation speed.

Keywords: cosmology
The Discovery of a Rotating Radio Transient J1918-0449 with Intriguing Emission Properties with the Five-hundred-meter Aperture Spherical Radio Telescope

In this study, we report on a detailed single-pulse analysis of the radio emission from a rotating radio transient (RRAT) J1918-0449, which is discovered with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The sensitive observations were carried out on 2021 April 30 using the FAST with a central frequency of 1250 MHz and a short time resolution of 49.152 μs, which forms a reliable basis to probe single-pulse emission properties in detail. The source was successively observed for around 2 hr. A total of 83 dispersed bursts with significance above 6σ are detected over 1.8 hr. The source's dispersion measure (DM) and rotational period are determined to be 116.1 ± 0.4 pc cm-3 and 2479.21 ± 0.03 ms, respectively. The share of registered pulses from the total number of observed periods is 3.12%. No underlying emission is detected in the averaged off-pulse profile. For bursts with fluence larger than 10 Jy ms, the pulse energy follows a power-law distribution with an index of -3.1 ± 0.4, suggesting the existence of bright pulse emission. We find that the distribution of time between subsequent pulses is consistent with a stationary Poisson process and find no evidence of clustering over the 1.8 hr observations, giving a mean burst rate of one burst every 66 s. Close inspection of the detected bright pulses reveals that 21 pulses exhibit well-defined quasiperiodicities. The subpulse drifting is present in nonsuccessive rotations with periodicity of 2.51 ± 0.06 periods. Finally, possible physical mechanisms are discussed.

Keywords: radio pulsars
Latitudinal Propagation of Thermal Rossby Waves in Stellar Convection Zones

Using an analytic model, we derive the eigenfrequencies for thermal Rossby waves that are trapped radially and latitudinally in an isentropically stratified atmosphere. We ignore the star's curvature and work in an equatorial f-plane geometry. The propagation of inertial waves is found to be sensitive to the relative direction of the wavevector to the zonal direction. Prograde propagating thermal Rossby waves are naturally trapped in the radial direction for frequencies above a critical threshold, which depends on the angle of propagation. Below the threshold frequency, there exists a continuous spectrum of prograde and retrograde inertial waves that are untrapped in an isentropic atmosphere but can be trapped by gradients in the specific entropy density. Finally, we discuss the implications of these waves on recent observations of inertial oscillations in the Sun, as well as in numerical simulations.

Keywords: solar convective zone; stellar convective zones; stellar oscillations; solar oscillations; stellar rotation; internal waves; hydrodynamics; asteroseismology; helioseismology; polytropes
Band-limited Features in the Primordial Power Spectrum Do Not Resolve the Hubble Tension

For a standard ΛCDM universe with a power-law primordial power spectrum, the discrepancy between early- and late-universe measurements of the Hubble constant continued to grow and recently reached 5.3σ. During inflation, local features in the inflationary potential often lead to band-limited features in the primordial power spectrum, hence breaking the power-law assumption in the derivation of the Hubble tension. We investigate whether such inflationary "glitches" can ease the Hubble tension. The recently released Planck temperature and polarization data and the 2019 SH0ES+H0LiCOW joint constraint on the Hubble constant are combined to drive a blind Daubechies wavelet signal search in the primordial power spectrum, up to a resolution ${\rm{\Delta }}\mathrm{ln}\,k\sim 0.1$ . We find no significant detection of any features beyond power law. With 64 more degrees of freedom injected in the primordial power spectrum, the Hubble tension persists at a 4.9σ level.

Keywords: cosmological models; cosmology; dark energy; observational cosmology; cosmological parameters; hubble constant
Investigating the Star Formation Rates of Active Galactic Nucleus Hosts Relative to the Star-forming Main Sequence

A fundamental question in galaxy and black hole evolution remains how galaxies and their supermassive black holes have evolved together over cosmic time. Specifically, it is still unclear how the position of X-ray active galactic nucleus (AGN) host galaxies with respect to the star-forming main sequence (MS) may change with the X-ray luminosity (L X) of the AGN or the stellar mass (M ⋆) of the host galaxy. We use data from the XMM-Spitzer Extragalactic Representative Volume Survey (XMM-SERVS) to probe this issue. XMM-SERVS is covered by the largest medium-depth X-ray survey (with superb supporting multiwavelength data) and thus contains the largest sample to date for study. To ensure consistency, we locally derive the MS from a large reference galaxy sample. In our analysis, we demonstrate that the turnover of the galaxy MS does not allow reliable conclusions to be drawn for high-mass AGNs, and we establish a robust safe regime where the results do not depend upon the choice of MS definition. Under this framework, our results indicate that less massive AGN host galaxies ( $\mathrm{log}{M}_{\star }\sim 9.5\mbox{--}10.5\,{M}_{\odot }$ ) generally possess enhanced star formation rates compared to their normal-galaxy counterparts while the more massive AGN host galaxies ( $\mathrm{log}{M}_{\star }\sim 10.5\mbox{--}11.5\,{M}_{\odot }$ ) lie on or below the star-forming MS. Further, we propose an empirical model for how the placement of an AGN with respect to the MS (SFRnorm) evolves as a function of both M ⋆ and L X.

Keywords: x-ray active galactic nuclei; agn host galaxies; galaxies
Evidence for a Highly Opaque Large-scale Galaxy Void at the End of Reionization

We present evidence that a region of high effective Lyα optical depth at z ∼ 5.7 is associated with an underdense region at the tail end of cosmic reionization. We carried out a survey of Lyman-break Galaxies (LBGs) using Subaru Hyper Suprime-Cam in the field of the z = 5.98 quasar J0148+0600, whose spectrum presents an unusually long (∼160 cMpc) and opaque (τ ≳ 7) Lyα trough at 5.5 ≤ z ≤ 5.9. LBG candidates were selected to lie within the redshift range of the trough, and the projected number densities were measured within 90 cMpc of the quasar sightline. The region within 8‧ (or ≈19 cMpc) of the quasar position is the most underdense of the whole field. The significance of the presence of the void is estimated to be 99%. This is consistent with the significant deficit of Lyα emitters (LAEs) at z = 5.72 reported by Becker et al. and suggests that the paucity of LAEs is not purely due to the removal of the Lyα emission by the high opacity but reflects a real coherent underdensity of galaxies across the entire redshift range of the trough. These observations are consistent with scenarios in which large optical depth fluctuations arise due to fluctuations in the galaxy-dominant UV background or due to residual neutral islands that are expected from reionization that is completed at redshifts as low as z ≲ 5.5.

Keywords: intergalactic medium; reionization; lyman-break galaxies; lyman alpha forest
Delensing of Cosmic Microwave Background Polarization with Machine Learning

Primordial B-mode detection is one of the main goals of next-generation cosmic microwave background (CMB) experiments. Primordial B-modes are a unique signature of primordial gravitational waves (PGWs). However, the gravitational interaction of CMB photons with large-scale structures will distort the primordial E modes, adding a lensing B-mode component to the primordial B-mode signal. Removing the lensing effect ("delensing") from observed CMB polarization maps will be necessary to improve the constraint of PGWs and obtain a primordial E-mode signal. Here, we introduce a deep convolutional neural network model named multi-input multi-output U-net (MIMO-UNet) to perform CMB delensing. The networks are trained on simulated CMB maps with size 20° × 20°. We first use MIMO-UNet to reconstruct the unlensing CMB polarization (Q and U) maps from observed CMB maps. The recovered E-mode power spectrum exhibits excellent agreement with the primordial EE power spectrum. The recovery of the primordial B-mode power spectrum for noise levels of 0, 1, and 2 μK-arcmin is greater than 98% at the angular scale of ℓ < 150. We additionally reconstruct the lensing B map from observed CMB maps. The recovery of the lensing B-mode power spectrum is greater than roughly 99% at the scales of ℓ > 200. We delens the observed B-mode power spectrum by subtracting the reconstructed lensing B-mode spectrum. The recovery of tensor B-mode power spectrum for noise levels of 0, 1, and 2 μK-arcmin is greater than 98% at the angular scales of ℓ < 120. Even at ℓ = 160, the recovery of tensor B-mode power spectrum is still around 71%.

Keywords: cosmic microwave background radiation; observational cosmology; convolutional neural networks