adsabs/SciX_UAT_keywords huggingface dataset:
Reinflation of Warm and Hot Jupiters

Understanding the anomalous radii of many transiting hot gas-giant planets is a fundamental problem of planetary science. Recent detections of reinflated warm Jupiters orbiting post-main-sequence stars and the reinflation of hot Jupiters while their host stars evolve on the main sequence may help constrain models for the anomalous radii of hot Jupiters. In this work, we present evolution models studying the reinflation of gas giants to determine how varying the depth and intensity of deposited heating affects both main-sequence reinflation of hot Jupiters and post-main-sequence reinflation of warm Jupiters. We find that deeper heating is required to reinflate hot Jupiters than is needed to suppress their cooling, and that the timescale of reinflation decreases with increasing heating rate and depth. We find a strong degeneracy between heating rate and depth, with either strong shallow heating or weak deep heating providing an explanation for main-sequence reinflation of hot Jupiters. This degeneracy between heating rate and depth can be broken in the case of post-main-sequence reinflation of warm Jupiters, as the inflation must be rapid to occur within post-main-sequence evolution timescales. We also show that the dependence of heating rate on the incident stellar flux inferred from the sample of hot Jupiters can explain reinflation of both warm and hot Jupiters. TESS will obtain a large sample of warm Jupiters orbiting post-main-sequence stars, which will help to constrain the mechanism(s) causing the anomalous radii of gas-giant planets.

Keywords: exoplanet evolution; extrasolar gaseous giant planets; hot jupiters; planetary interior; stellar evolution; planetary structure
Stellar Models of Betelgeuse Constrained Using Observed Surface Conditions

We study stellar models for Betelgeuse using the HR diagram and surface abundances as observational constraints. Previous studies on Betelgeuse have not systematically investigated the surface abundances, but we believe they can be impacted by, and thus be used as an observational constraint for various parameters such as initial mass, rotation, and overshoot scheme. We investigate stellar models with varying initial mass as they evolve past the main sequence, and we examine the red supergiant (RSG) properties in detail. For each mass, we vary the initial rotation up to ~300 km s-1, and test two different overshoot parameters. Overall, the acceptable initial mass range is 12-25 M ⊙, but for nonrotating models only, the range is decreased to 15-24 M ⊙. Also for rotating models, we find that v/v K = 0.3 is the upper limit for initial rotation, as more rapidly rotating models are unable to fit to Betelgeuse's surface abundances as an RSG. In addition, we report two possibilities for the current stage of evolution, core helium burning or core carbon burning and beyond. We find that certain 17 M ⊙ models could fit both stages. Finally, we discuss the implications of our results in the context of merger scenarios which have been suggested as a mechanism to attain the observed surface velocity of Betelgeuse.

Keywords: red supergiant stars; stellar rotation; stellar evolution
Dynamical Structure of Small Bulges Reveals Their Early Formation in ΛCDM Paradigm

The Λ cold dark matter (ΛCDM) paradigm of galaxy formation predicts that dense spheroidal stellar structures invariably grow at early cosmic time. These primordial spheroids evolve toward a virialized dynamical status as they finally become today's elliptical galaxies and large bulges at the center of disk galaxies. However, observations reveal that small bulges in spiral galaxies are common in the nearby universe. The prevailing belief that all small bulges form at later times from internal processes occurring in the disk represents a challenge for the ΛCDM scenario. Notably, the coevolution of bulges and central supermassive black holes (SMBHs) at early phases of galaxy evolution is also at stake. However, observations have so far not provided conclusive evidence against their possible early origin. Here, we report new observations of small bulges showing that they follow the mass-velocity dispersion relation expected for virialized systems. Contrary to previous claims, small bulges bridge the gap between massive ellipticals and globular clusters. This dynamical picture supports a scenario where systems over seven orders of magnitude in stellar mass form at early cosmic time. These results alleviate the tension between ΛCDM simulations and observations at galactic scales. We hypothesize that these small bulges are actually the low-mass descendants of compact objects observed at high redshift, also known as red nuggets, which are consistently produced in cosmological ΛCDM simulations. Therefore, this also suggests that the established coevolution of SMBHs and large bulges naturally extends to spheroids in the low-mass regime.

Keywords: low surface brightness galaxies; late-type galaxies; galaxy physics; compact galaxies; galaxies; disk galaxies; early-type galaxies; elliptical galaxies; galaxy formation; galaxy dynamics; galaxy properties; galaxy structure
A Second Look at 12 Candidate Dual AGNs Using BAYMAX

We present an analysis of 12 optically selected dual active galactic nucleus (AGN) candidates at z < 0.34. Each candidate was originally identified via double-peaked [O III] λ5007 emission lines and received follow-up Chandra and Hubble Space Telescope (HST) observations. Because the X-ray data are low-count (<100 counts) with small separations (<1″), a robust analysis is necessary for classifying each source. Pairing long-slit [O III] observations with existing Chandra observations, we re-analyze the X-ray observations with Bayesian AnalYsis of AGNs in X-rays to determine whether the X-ray emission from each system is more likely a single or dual point source. We find that 4 of the 12 sources are likely dual X-ray point-source systems. We examine each point source's spectra via a Monte Carlo method that probabilistically identifies the likely origin of each photon. When doing so, we find that (I) the secondary X-ray point sources in two of the systems have LX < 1040 erg s-1, such that we cannot rule out a non-AGN origin, (II) one source has a secondary with LX > 1040 erg s-1 but a spectrum that is too soft to definitively preclude being X-ray emitting diffuse gas that was photoionized by the primary AGN, and (III) one system (SDSS J1126+2944) is a dual AGN. Additionally, using complementary HST observations, we analyze a subsample of systems that are visually identified as merging. Our results suggest that dual AGNs may preferentially reside in mergers with small separations, consistent with both simulations and observations.

Keywords: active galactic nuclei; agn host galaxies; galaxy mergers; x-ray astronomy
Identification of Possible Heat Sources for the Thermal Output of Enceladus

We have calculated the amount of radioactive heat production (RHP) that could possibly prevent the postulated underground ocean of Enceladus from freezing. An internal heat source is necessary to justify the observed heat output from Enceladus and to allow the tidal dissipation heating models to work. Also based on the terrestrial evidence, we have assumed that the most common radiogenic element that can produce such internal heat is 238U. Our results show that a minimum amount in the range 38.10-76.59 ppm of 238U, averaged over the whole mass of Enceladus, is necessary to obtain the required RHP. The range of values increases to 63.60-127.70 ppm if we consider only the mass of the rocky portion and 2890-5775 ppm if we consider the mass of the rock + ice portion of Enceladus just below the southern polar area. Even in the latter case, the concentration of uranium is still well below the amount found in high-grade ore on Earth.

Keywords: saturnian satellites; tidal interaction; planetary interior
Coronal Electron Densities Derived with Images Acquired during the 2017 August 21 Total Solar Eclipse

The total solar eclipse of 2017 August 21 was observed with a digital single lens reflex (DSLR) camera equipped with a linear polarizing filter. A method was developed to combine images acquired with 15 different exposure times (from 1/4000 s to 4 s), identifying in each pixel the best interval of detector linearity. The resulting mosaic image of the solar corona extends up to more than 5 solar radii, with a projected pixel size of 3.7 arcsec/pixel and an effective image resolution of 10"2, as determined with visible α-Leo and ν-Leo stars. Image analysis shows that in the inner corona the intensity gradients are so steep that nearby pixels show a relative intensity difference of up to ∼10%; this implies that care must be taken when analyzing single exposures acquired with polarization cameras. Images acquired with two different orientations of the polarizer have been analyzed to derive the degree of linear polarization and the polarized brightness pB in the solar corona. After intercalibration with pB measurements by the K-Cor instrument on Mauna Loa Solar Observatory (MLSO), the data analysis provided the 2D coronal electron density distribution from 1.1 up to ∼3 solar radii. The absolute radiometric calibration was also performed with the full Sun image and with magnitudes of visible stars. The resulting absolute calibrations show a disagreement by a factor of ∼2 with respect to MLSO; interestingly, this is the same disagreement recently found with eclipse predictions provided by MHD numerical simulations.

Keywords: solar corona; ground-based astronomy; solar eclipses; total eclipses; polarimetry; polarimeters; amateur astronomy; amateur astronomers; visual observation; coronagraphic imaging; ccd photometry; photometry
EAGLE and Illustris-TNG Predictions for Resolved eROSITA X-Ray Observations of the Circumgalactic Medium around Normal Galaxies

We simulate stacked observations of nearby hot X-ray coronae associated with galaxies in the EAGLE and Illustris-TNG hydrodynamic simulations. A forward modeling pipeline is developed to predict 4 yr eROSITA observations and stacked image analysis, including the effects of instrumental and astrophysical backgrounds. We propose an experiment to stack z ≈ 0.01 galaxies separated by specific star formation rate (sSFR) to examine how the hot (T ≥ 106 K) circumgalactic medium (CGM) differs for high- and low-sSFR galaxies. The simulations indicate that the hot CGM of low-mass ( ${M}_{* }\approx {10}^{10.5}\ {M}_{\odot }$ ), high-sSFR (defined as the top one-third ranked by sSFR) central galaxies will be detectable to a galactocentric radius r ≈ 30-50 kpc. Both simulations predict lower luminosities at fixed stellar mass for the low-sSFR galaxies (the lower third of sSFR) with Illustris-TNG predicting 3× brighter coronae around high-sSFR galaxies than EAGLE. Both simulations predict detectable emission out to r ≈ 150-200 kpc for stacks centered on high-mass ( ${M}_{* }\approx {10}^{11.0}\ {M}_{\odot }$ ) galaxies, with EAGLE predicting brighter X-ray halos. The extended soft X-ray luminosity correlates strongly and positively with the mass of circumgalactic gas within the virial radius (fCGM). Prior analyses of both simulations have established that fCGM is reduced by expulsive feedback driven mainly by black hole growth, which quenches galaxy growth by inhibiting replenishment of the interstellar medium. Both simulations predict that eROSITA stacks should not only conclusively detect and resolve the hot CGM around L* galaxies for the first time, but provide a powerful probe of how the baryon cycle operates, for which there remains an absence of consensus between state-of-the-art simulations.

Keywords: circumgalactic medium; galactic winds; galaxy formation; x-ray observatories; hydrodynamical simulations; supermassive black holes
Friends Not Foes: Strong Correlation between Inner Super-Earths and Outer Gas Giants

The connection between outer gas giants and inner super-Earths reflects their formation and evolutionary histories. Past work exploring this link has suggested a tentative positive correlation between these two populations, but these studies have been limited by small sample sizes and in some cases sample biases. Here we take a new look at this connection with a sample of 184 super-Earth systems with publicly available radial velocity data and resolved outer gas giants. We calculate the frequency of outer gas giants (GG) in super-Earth (SE) systems, dividing our sample into metal-rich ([Fe/H] > 0) and metal-poor ([Fe/H]≤0) hosts. We find P(GG∣SE, [Fe/H]>0) = and P(GG∣SE, [Fe/H]≤0) = . Comparing these conditional occurrence rates to field giant occurrence rates from Rosenthal et al. (2021), we show that there is a distinct positive correlation between inner super-Earths and outer gas giants for metal-rich host stars at the 2.7σ level, but this correlation disappears for metal-poor systems. We further find that, around metal-rich stars, the GG/SE correlation enhances slightly for systems with giants that are more distant (beyond 3 au), more eccentric (e > 0.2), and/or in multi-gas giant systems. Such trends disappear around metal-poor stars with the exception of systems of multiple giants in which we observe a tentative anti-correlation. Our findings highlight the critical role metallicity (disk solid budget) plays in shaping the overall planetary architecture.

Keywords: exoplanet astronomy; exoplanet evolution; exoplanet formation
Modeling Dust Production, Growth, and Destruction in Reionization-era Galaxies with the CROC Simulations. II. Predicting the Dust Content of High-redshift Galaxies

We model the interstellar dust content of the reionization era with a suite of cosmological, fluid-dynamical simulations of galaxies with stellar masses ranging from ∼105 to 109 M ⊙ in the first 1.2 Gyr of the Universe. We use a post-processing method that accounts for dust creation and destruction processes, allowing us to systematically vary the parameters of these processes to test whether dust-dependent observable quantities of galaxies at these epochs could be useful for placing constraints on dust physics. We then forward model observable properties of these galaxies to compare to existing data. We find that we are unable to simultaneously match existing observational constraints with any one set of model parameters. Specifically, the models that predict the largest dust masses D/Z ≳ 0.1 at z = 5—because of high assumed production yields and/or efficient growth via accretion in the interstellar medium—are preferred by constraints on total dust mass and infrared (IR) luminosities, but these models produce far too much attenuation in the ultraviolet (UV), preventing them from matching observations of β UV. To investigate this discrepancy, we analyze the relative spatial distribution of stars and dust as probed by IR and UV emission, which appear to exhibit overly symmetric morphologies compared to existing data, likely due to the limitations of the stellar feedback model used in the simulations. Our results indicate that the observable properties of the dust distribution in high redshift galaxies are a particularly strong test of stellar feedback.

Keywords: hydrodynamical simulations; galaxy formation; cosmology; astronomical simulations
Single-band VLBI Absolute Astrometry

The ionospheric path delay impacts single-band, very long baseline interferometry (VLBI) group delays, which limits their applicability for absolute astrometry. I consider two important cases: when observations are made simultaneously in two bands, but delays in only one band are available for a subset of observations; and when observations are made in one-band design. I developed optimal procedures of data analysis for both cases using Global Navigation Satellite System (GNSS) ionosphere maps, provided a stochastic model that describes ionospheric errors, and evaluated their impact on source position estimates. I demonstrate that the stochastic model is accurate at a level of 15%. I found that using GNSS ionospheric maps as is introduces serious biases in estimates of declination and I developed a procedure that almost eliminates them. I found serendipitously that GNSS ionospheric maps have multiplicative errors and have to be scaled by 0.85 in order to mitigate the declination bias. A similar scale factor was found in comparison of the vertical total electron content from satellite altimetry against GNSS ionospheric maps. I favor interpretation of this scaling factor as a manifestation of the inadequacy of the thin-shell model of the ionosphere. I showed that we are able to model the ionospheric path delay to the extent that no noticeable systematic errors emerge and we are able to assess adequately the contribution of the ionosphere-driven random errors on source positions. This makes single-band absolute astrometry a viable option that can be used for source position determination.

Keywords: radio astrometry; earth ionosphere; very long baseline interferometry
Flare Rates, Rotation Periods, and Spectroscopic Activity Indicators of a Volume-complete Sample of Mid- to Late-M Dwarfs within 15 pc

We present a study of flare rates, rotation periods, and spectroscopic activity indicators of 125 single stars within 15 parsecs and with masses between 0.1 and 0.3 M⊙ observed during the first year of the TESS mission, with the goal of elucidating the relationship between these various magnetically connected phenomena. We gathered multiepoch high-resolution spectra of each target, and we measured equivalent widths of the activity indicators helium I D3, Hα, and the calcium infrared triplet line at 8542.09 Å. We present 18 new rotation periods from MEarth photometry and 19 new rotation periods from TESS photometry. We present a catalog of 1392 flares. After correcting for sensitivity, we find the slope of the flare frequency distribution for all stars to have a standard value of α = 1.98 ± 0.02. We determine R31.5, the rate of flares per day with energies above E = 3.16 × 1031 ergs in the TESS bandpass. We find that below a critical value of Hα EW = -0.71 Å, log R31.5 increases linearly with increasing Hα emission; above this value, log R31.5 declines rapidly. The stars divide into two groups: 26% have Hα in emission, high flare rates with typical values of log R31.5 = -1.30 ± 0.08, and have Rossby numbers <0.50. The remaining 74% show little to no Hα in emission and exhibit log R31.5 < -3.86, with the majority of these stars not showing a single flare during the TESS observations.

Keywords: stellar activity; stellar rotation; stellar flares
Electromagnetic Turbulence in the Electron Current Layer to Drive Magnetic Reconnection

Magnetic reconnection is a natural energy converter that can have a significant impact on global processes in space, astrophysics, and fusion plasmas. Macroscopic modeling of reconnection is crucial in understanding the global responses to local kinetic processes. The key issue in developing the reconnection model is the description of the magnetic dissipation around the x-line to drive reconnection. In collisionless plasma, the dissipation can be generated by plasma turbulence through wave-particle interactions. However, the mechanisms to yield turbulence and dissipation in the reconnection current layer are currently poorly understood. In this study, we show, using three-dimensional particle-in-cell simulations, that the electron Kelvin-Helmholtz instability plays a primary role in driving intense electromagnetic turbulence leading to the dissipation and electron heating. We find that the ions hardly react to the turbulence, which indicates that the turbulence does not cause significant momentum exchange between electrons and ions resulting in electrical resistivity. It is demonstrated that the dissipation is mainly caused by viscosity associated with electron momentum transport across the current layer. The present results suggest a fundamental modification of the current magnetohydrodynamics models using the resistivity to generate the dissipation.

Keywords: space plasmas; plasma astrophysics; geomagnetic fields; interplanetary turbulence; magnetohydrodynamical simulations
The Cosmic Ultraviolet Baryon Survey (CUBS). II. Discovery of an H2-bearing DLA in the Vicinity of an Early-type Galaxy at z = 0.576

We report the serendipitous detection of an H2-bearing damped Lyα absorber at z = 0.576 in the spectrum of the QSO J0111-0316 in the Cosmic Ultraviolet Baryon Survey. Spectroscopic observations from Hubble Space Telescope-COS in the far-ultraviolet reveal a damped absorber with log[N(H I)/cm-2] = 20.1 ± 0.2 and log[N(H2)/cm-2] $={18.97}_{-0.06}^{+0.05}$ . The diffuse molecular gas is found in two velocity components separated by Δ ν ≈ 60 km s-1, with >99.9% of the total H2 column density concentrated in one component. At a metallicity of ≈50% of solar, there is evidence for Fe enhancement and dust depletion, with a dust-to-gas ratio κO ≈ 0.4. A galaxy redshift survey conducted with IMACS and LDSS-3C on Magellan reveals an overdensity of nine galaxies at projected distance d ≤ 600 proper kpc (pkpc) and line-of-sight velocity offset Δ νg ≤ 300 km s-1 from the absorber. The closest is a massive, early-type galaxy at d = 41 pkpc that contains ≈70% of the total stellar mass identified at d ≤ 310 pkpc of the H2 absorber. The close proximity of the H2-bearing gas to the quiescent galaxy and the Fe-enhanced chemical abundance pattern of the absorber suggest a physical connection, in contrast to a picture in which DLAs are primarily associated with gas-rich dwarfs. This case study illustrates that deep galaxy redshift surveys are needed to gain insight into the diverse environments that host dense and potentially star-forming gas. * Based on data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory and the NASA/ESA Hubble Space Telescope operated by the Space Telescope Science Institute and the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

Keywords: circumgalactic medium; extragalactic astronomy; quasar absorption line spectroscopy; interstellar molecules; interstellar medium; galaxy groups
The Behavior of Bp He-weak Stars in the Far UV-Paper IV: HD 28843

The analysis of five spectra of the Bp He-weak Si star HD 28843 recorded by the SWP camera on board the International Ultraviolet Explorer reveals variations of the far-ultraviolet spectral energy distribution over a time interval of 4 yr and eight months. Variations are present shortwards of 1700 Å which can be partly attributed to variations of lines and continuum of Si II. Other lines due to C II and Si III also contribute to the opacity in this range too. The variations suggest that silicon is not distributed in a uniform manner over the surface and that the horizontal gradients of the silicon abundance are probably quite large.

Keywords: chemically peculiar stars; helium-weak stars
Brown Dwarfs are Violet: A New Calculation of Human-eye Colors of Main-sequence Stars and Substellar Objects

There has always been interest in the perceived colors of stars. They were key to the development of the Hertzsprung-Russell diagram, and they are also used widely in educational and public-outreach imagery. Thus, it is useful to develop tools to compute these colors from spectral energy distributions. This paper presents a collection of objective (CIE coordinate) and subjective (RGB triple) colors for main-sequence stars and brown dwarfs, as well as links to related codes and tables. Using the proposed conversion from CIE to RGB colors, O and B stars are bluer than equivalent blackbodies because of Paschen continuum absorption, and M dwarfs tend to be less red and more beige. Although brown dwarfs over a wide range of effective temperatures (400-2000 K) emit most of their flux in the infrared, their visible spectra are dominated by short wavelengths. Thus, they may appear violet to human eyes.

Keywords: brown dwarfs; late-type stars; spectroscopy; stellar atmospheres; stellar colors