adsabs/SciX_UAT_keywords huggingface dataset:
Persistent Non-Gaussian Structure in the Image of Sagittarius A* at 86 GHz

Observations of the Galactic Center supermassive black hole Sagittarius A* (Sgr A*) with very long-baseline interferometry (VLBI) are affected by interstellar scattering along our line of sight. At long radio observing wavelengths (≲1 cm), the scattering heavily dominates image morphology. At 3.5 mm (86 GHz), the intrinsic source structure is no longer sub-dominant to scattering, and thus the intrinsic emission from Sgr A* is resolvable with the Global Millimeter VLBI Array (GMVA). Long-baseline detections to the phased Atacama Large Millimeter/submillimeter Array (ALMA) in 2017 provided new constraints on the intrinsic and scattering properties of Sgr A*, but the stochastic nature of the scattering Requires multiple observing epochs to reliably estimate its statistical properties. We present new observations with the GMVA+ALMA, taken in 2018, which confirm non-Gaussian structure in the scattered image seen in 2017. In particular, the ALMA-GBT baseline shows more flux density than expected for an anistropic Gaussian model, providing a tight constraint on the source size and an upper limit on the dissipation scale of interstellar turbulence. We find an intrinsic source extent along the minor axis of ~100 μas both via extrapolation of longer wavelength scattering constraints and direct modeling of the 3.5 mm observations. Simultaneously fitting for the scattering parameters, we find an at-most modestly asymmetrical (major-to-minor axis ratio of 1.5 ± 0.2) intrinsic source morphology for Sgr A*.

Keywords: black holes; galactic center; very long baseline interferometry; radio interferometry; interstellar medium
A Systematic Study of the Short-term X-Ray Variability of Seyfert Galaxies. I. Diversity of the X-Ray rms Spectra

The X-ray variability of active galactic nuclei (AGN) carries crucial information about the X-ray radiation mechanism. We performed a systematic study of the X-ray short-term (1-100 ks timescale) variability for a large sample of 78 Seyferts with 426 deep XMM-Newton observations. In this paper, we present the time-averaged spectra and rms spectra for the entire sample, which show a variety of properties. Based on the spectral shape, we divide the rms spectra into five subtypes and the time-averaged spectra into four subtypes. The most common shape of the rms spectra is concave-down where the rms peaks at ~1 keV. We find that different sources can show similar time-averaged spectra and rms spectra. However, there is no one-to-one mapping between the subtypes of the time-averaged spectra and rms spectra, as similar time-averaged spectra can be accompanied by different rms spectra, and vice versa. This is likely because different physical mechanisms can produce similar rms spectra. For every subtype of the time-averaged spectra, we report its preferred subtypes of the rms spectra in both low- and high-frequency bands. We also compare the statistical properties for different subtypes, such as the black hole mass and Eddington ratio. Finally, we investigate the rms in the Fe Kα line regime and find that those with a broad and extended red-wing profile tend to show stronger variability than those showing a narrow or relatively symmetric profile. Our results demonstrate the necessity of performing joint spectral and variability modeling in order to understand the mechanism of the X-ray emission in AGN. All of the rms spectra have been made publicly available.

Keywords: x-ray active galactic nuclei
AWSoM Magnetohydrodynamic Simulation of a Solar Active Region with Realistic Spectral Synthesis

For the first time, we simulate the detailed spectral line emission from a solar active region (AR) with the Alfvén Wave Solar Model (AWSoM). We select an AR appearing near disk center on 2018 July 13 and use the National Solar Observatory's Helioseismic and Magnetic Imager synoptic magnetogram to specify the magnetic field at the model's inner boundary. To resolve small-scale magnetic features, we apply adaptive mesh refinement with a horizontal spatial resolution of 0°.35 (4.5 Mm), four times higher than the background corona. We then apply the SPECTRUM code, using CHIANTI spectral emissivities, to calculate spectral lines forming at temperatures ranging from 0.5 to 3 MK. Comparisons are made between the simulated line intensities and those observed by Hinode/Extreme-ultraviolet Imaging Spectrometer where we find close agreement across a wide range of loop sizes and temperatures (about 20% relative error for both the loop top and footpoints at a temperature of about 1.5 MK). We also simulate and compare Doppler velocities and find that simulated flow patterns are of comparable magnitude to what is observed. Our results demonstrate the broad applicability of the low-frequency AWSoM for explaining the heating of coronal loops.

Keywords: solar corona; spectrophotometry; magnetohydrodynamics; magnetohydrodynamical simulations; solar coronal waves
A Search for Rotation Periods in 1000 TESS Objects of Interest

The high-quality light curves from the Transiting Exoplanet Survey Satellite (TESS) represent a unique laboratory for the study of stellar rotation, which is a fundamental observable driving stellar and planetary evolution, including planetary atmospheres and impacting habitability conditions and the genesis of life around stars. As of 2020 April 14, this mission delivered public light curves for 1000 TESS objects of interest (TOIs), observed with a 2 minute cadence during the first 20 months of the mission. Here, we present a search for rotation signatures in these TOIs, using fast Fourier transform, Lomb-Scargle, and wavelet techniques, accompanied by a rigorous visual inspection. This effort revealed 163 targets with rotation signatures, 131 of which present unambiguous rotation periods ranging from 0.321 and 13.219 days, whereas 32 of them present dubious rotation periodicities. Of these stars, 109 show flux fluctuations whose root cause is not clearly identified. For 714 TOIs, the light curves show a noisy behavior, corresponding to typically low-amplitude signals. Our analysis has also revealed 10 TOI stars with pulsation periodicities ranging from 0.049 to 2.995 days and four eclipsing binaries. With upcoming TESS data releases, our periodicity analysis will be expanded to almost all TOI stars, thereby contributing in defining criteria for follow-up strategy itself, and the study of star-planet interactions, surface dynamic of host stars, and habitability conditions in planets, among other aspects. In this context, a living catalog is maintained on the Filtergraph visualization portal at https://filtergraph.com/tess_rotation_tois.

Keywords: stellar rotation; exoplanet catalogs; stellar photometry; variable stars; stellar pulsations
A Perspective on the Milky Way Bulge Bar as Seen from the Neutron-capture Elements Cerium and Neodymium with APOGEE

This study probes the chemical abundances of the neutron-capture elements cerium and neodymium in the inner Milky Way from an analysis of a sample of ∼2000 stars in the Galactic bulge bar spatially contained within ∣X Gal∣ < 5 kpc, ∣Y Gal∣ < 3.5 kpc, and ∣Z Gal∣ < 1 kpc, and spanning metallicities between ‑2.0 ≲ [Fe/H] ≲ +0.5. We classify the sample stars into low- or high-[Mg/Fe] populations and find that, in general, values of [Ce/Fe] and [Nd/Fe] increase as the metallicity decreases for the low- and high-[Mg/Fe] populations. Ce abundances show a more complex variation across the metallicity range of our bulge-bar sample when compared to Nd, with the r-process dominating the production of neutron-capture elements in the high-[Mg/Fe] population ([Ce/Nd] < 0.0). We find a spatial chemical dependence of Ce and Nd abundances for our sample of bulge-bar stars, with low- and high-[Mg/Fe] populations displaying a distinct abundance distribution. In the region close to the center of the MW, the low-[Mg/Fe] population is dominated by stars with low [Ce/Fe], [Ce/Mg], [Nd/Mg], [Nd/Fe], and [Ce/Nd] ratios. The low [Ce/Nd] ratio indicates a significant contribution in this central region from r-process yields for the low-[Mg/Fe] population. The chemical pattern of the most metal-poor stars in our sample suggests an early chemical enrichment of the bulge dominated by yields from core-collapse supernovae and r-process astrophysical sites, such as magnetorotational supernovae.

Keywords: galaxy abundances; galaxy bulges; galaxy evolution; milky way evolution
Multiwavelength Variability of Sagittarius A* in 2019 July

We report a timing analysis of near-infrared (NIR), X-ray, and submillimeter data during a 3 day coordinated campaign observing Sagittarius A*. Data were collected at 4.5 μm with the Spitzer Space Telescope, 2-8 keV with the Chandra X-ray Observatory, 3-70 keV with NuSTAR, 340 GHz with ALMA, and 2.2 μm with the GRAVITY instrument on the Very Large Telescope Interferometer. Two dates show moderate variability with no significant lags between the submillimeter and the infrared at 99% confidence. A moderately bright NIR flare (F K ~ 15 mJy) was captured on July 18 simultaneous with an X-ray flare (F 2-10 keV ~ 0.1 counts s-1) that most likely preceded bright submillimeter flux (F 340 GHz ~ 5.5 Jy) by about $+{34}_{-33}^{+14}$ minutes at 99% confidence. The uncertainty in this lag is dominated by the fact that we did not observe the peak of the submillimeter emission. A synchrotron source cooled through adiabatic expansion can describe a rise in the submillimeter once the synchrotron self-Compton NIR and X-ray peaks have faded. This model predicts high GHz and THz fluxes at the time of the NIR/X-ray peak and electron densities well above those implied from average accretion rates for Sgr A*. However, the higher electron density postulated in this scenario would be in agreement with the idea that 2019 was an extraordinary epoch with a heightened accretion rate. Since the NIR and X-ray peaks can also be fit by a nonthermal synchrotron source with lower electron densities, we cannot rule out an unrelated chance coincidence of this bright submillimeter flare with the NIR/X-ray emission.

Keywords: galactic center; black hole physics; accretion; non-thermal radiation sources; supermassive black holes
Measuring the Cosmic X-Ray Background in 3-20 KeV with Stray Light from NuSTAR

By characterizing the contribution of stray light to large data sets from the CXB Measurement X-ray observatory collected over 2012-2017, we report a measurement of the cosmic X-ray background (CXB) in the 3-20 keV energy range. These data represent ~20% sky coverage while avoiding Galactic ridge X-ray emission and are less weighted by deep survey fields than previous measurements with CXB Measurement. Images in narrow energy bands are stacked in detector space and spatially fit with a model representing the stray light and uniform pattern expected from the CXB and the instrumental background, respectively. We establish baseline flux values from Earth-occulted data and validate the fitting method on stray-light observations of the Crab, which further serve to calibrate the resulting spectra. We present independent spectra of the CXB with the focal plane module FPMA and FPMB detector arrays, which are in excellent agreement with the canonical characterization by HEAO 1 and are 10% lower than most subsequent measurements: ${F}_{3-20\,\mathrm{keV}}^{\mathrm{FPMA}}=2.63\times {10}^{-11}\,\mathrm{erg}\,{{\rm{s}}}^{-1}\,{\mathrm{cm}}^{-2}\,{\deg }^{-2}$ and ${F}_{3\mbox{--}20\,\mathrm{keV}}^{\mathrm{FPMB}}\,=2.58\times {10}^{-11}\,\mathrm{erg}\,{{\rm{s}}}^{-1}\,{\mathrm{cm}}^{-2}\,{\deg }^{-2}$ . We discuss these results in light of previous measurements of the CXB and consider the impact of systematic uncertainties on our spectra.

Keywords: cosmic background radiation; active galactic nuclei; diffuse x-ray background; astronomy data analysis; x-ray surveys
The Variable Earth's Rotation in the 4th-7th Centuries: New ΔT Constraints from Byzantine Eclipse Records

As one of the greatest astronomical spectacles, total solar eclipses have long been a subject of scientific interest and have been recorded by numerous civilizations over the millennia. These records are an essential reference for constraining and reconstructing Earth's variable rotation (ΔT) prior to the 17th century. However, ΔT reconstructions for the 4th-7th centuries have significant uncertainties, mainly owing to a data scarcity. Here, we analyze Byzantine historical sources with reports of total solar eclipses along the Eastern Mediterranean coasts and add probable ΔT constraints on their basis. We examined five cases of total solar eclipses in 346, 418, 484, 601, and 693 CE, identified times and locations of the observations, and compared them with the existing ΔT spline curve to derive new ΔT constraints. Our results probably tighten ΔT variability in 346 CE, show a larger ΔT range in 418 CE, and give smaller ΔT ranges in 484, 601, and 693 CE. Our study tightens the existing ΔT variations and occasionally support some ΔT constraints that slightly depart from the ΔT spline curve in the latest reconstructions. Our results are consistent with contemporary ΔT constraints from other studies and offer an improved understanding of Earth's variable rotation.

Keywords: eclipses; solar eclipses; total eclipses; earth (planet)
Resolved Star Formation in TNG100 Central and Satellite Galaxies

Recent cosmological hydrodynamical simulations have produced populations of numerical galaxies whose global star-forming properties are in good agreement with those of observed galaxies. Proper modeling of energetic feedback from supernovae and active galactic nuclei is critical to the ability of simulations to reproduce observed galaxy properties, and historically, such modeling has proven to be a challenge. Here, we analyze the local properties of central and satellite galaxies in the z = 0 snapshot of the TNG100 simulation as a test of feedback models. We generate a face-on projection of stellar particles in TNG100 galaxies, from which we demonstrate the existence of a resolved star-forming main sequence (ΣSFR-Σ* relation) with a slope and normalization that is in reasonable agreement with previous studies. We also present radial profiles of various galaxy populations for two parameters: the distance from the resolved main-sequence line (ΔΣSFR) and the luminosity-weighted stellar age (Age L ). We find that, on average, high-mass central and satellite galaxies quench from the inside out, while low-mass central and satellite galaxies have similar, flatter profiles. Overall, we find that, with the exception of the starburst population, the TNG100 feedback models yield simulated galaxies whose radial distributions of Age L and ΔΣSFR agree with those of observed galaxies.

Keywords: galaxy evolution; star formation; galaxy quenching; astronomical simulations
HATS-37Ab and HATS-38b: Two Transiting Hot Neptunes in the Desert

We report the discovery of two transiting Neptunes by the HATSouth survey. The planet HATS-37Ab has a mass of $0.099\pm 0.042$ ${M}_{{\rm{J}}}$ (31.5 ± 13.4 M⊕) and a radius of $0.606\pm 0.016$ ${R}_{{\rm{J}}}$ , and is on a $P=4.3315$ day orbit around a $V=12.266\pm 0.030$ mag, ${0.843}_{-0.012}^{+0.017}$ ${M}_{\odot }$ star with a radius of ${0.877}_{-0.012}^{+0.019}$ ${R}_{\odot }$ . We also present evidence that the star HATS-37A has an unresolved stellar companion HATS-37B, with a photometrically estimated mass of $0.654\pm 0.033$ ${M}_{\odot }$ . The planet HATS-38b has a mass of $0.074\pm 0.011$ ${M}_{{\rm{J}}}$ (23.5 ± 3.5 M⊕) and a radius of $0.614\pm 0.017$ ${R}_{{\rm{J}}}$ , and is on a $P=4.3750$ day orbit around a $V=12.411\pm 0.030$ mag, ${0.890}_{-0.012}^{+0.016}$ ${M}_{\odot }$ star with a radius of $1.105\pm 0.016$ ${R}_{\odot }$ . Both systems appear to be old, with isochrone-based ages of ${11.46}_{-1.45}^{+0.79}$ Gyr, and $11.89\pm 0.60$ Gyr, respectively. Both HATS-37Ab and HATS-38b lie in the Neptune desert and are thus examples of a population with a low occurrence rate. They are also among the lowest-mass planets found from ground-based wide-field surveys to date. * The HATSouth network is operated by a collaboration consisting of Princeton University (PU), the Max Planck Institute für Astronomie (MPIA), the Australian National University (ANU), and Universidad Adolfo Ibáñez (UAI). The station at Las Campanas Observatory of the Carnegie Institution for Science is operated by PU in conjunction with UAI, the station at the High Energy Spectroscopic Survey site is operated in conjunction with MPIA, and the station at Siding Spring Observatory (SSO) is operated jointly with ANU. This work is based in part on observations made with the MPG 2.2 m Telescope at the ESO Observatory in La Silla and based on observations collected at the European Southern Observatory under ESO programmes 094.C-0428(A), 095.C-0367(A), 097.C-0571(A), 098.C-0292(A), 099.C-0374(A), 0100.C-0406(A), 0100.C-0406(B). This paper includes data gathered with the 6.5 m Magellan Telescopes at Las Campanas Observatory, Chile, and is based in part on observations made with the Anglo-Australian Telescope operated by the Australian Astronomical Observatory.

Keywords: exoplanets; hot neptunes
Abundances of Light Elements in the B8 Mn Star HD 110073

The synthesis of spectral intervals in the optical range allows the determination of LTE abundances of several chemical elements lighter than titanium for HD 110073. Compared to the solar abundances, helium, magnesium, oxygen, aluminum, silicon and calcium are underabundant by factors of 0.4, 0.25, 0.90, 0.20, 0.85, 0.5 times the respective solar abundances. Carbon and sulfur have solar abundances. Phosphorus and scandium are overabundant by factors of 10 and 30 times their solar abundances. These new determinations differ from previous determinations partly because the atomic data have changed. A non-uniform distribution of the elements over the surface of HD 110073 could also account for the differences.

Keywords: chemically peculiar stars; mercury-manganese stars
The Central Kinematics and Black Hole Mass of 4C+37.11

We report on integral field unit (IFU) measurements of the host of the radio source 4C+37.11. This massive elliptical contains the only resolved double compact nucleus at parsec-scale separation, likely a bound supermassive black hole binary (SMBHB). i-band photometry and GMOS-N IFU spectroscopy show that the galaxy has a large r b = 1.″5 core and that the stellar velocity dispersion increases inside of a radius of influence r SOI ≈ 1.″3. Jeans Anisotropic Modeling analysis of the core infers a total SMBHB mass of ${2.8}_{-0.8}^{+0.8}\times {10}^{10}{M}_{\odot }$ , making this one of the most massive black hole systems known. Our data indicate that there has been significant scouring of the central kiloparsec of the host galaxy.

Keywords: supermassive black holes; giant elliptical galaxies; brightest cluster galaxies
The CGM2 Survey: Quenching and the Transformation of the Circumgalactic Medium

This study addresses how the incidence rate of strong O VI absorbers in a galaxy's circumgalactic medium (CGM) depends on galaxy mass and, independently, on the amount of star formation in the galaxy. We use Hubble Space Telescope/Cosmic Origins Spectrograph absorption spectroscopy of quasars to measure O VI absorption within 400 projected kpc and 300 km s-1 of 52 galaxies with M * ~ 3 × 1010 M ⊙. The galaxies have redshifts 0.12 < z < 0.6, stellar masses 1010.1 M ⊙ < M * < 1010.9 M ⊙, and spectroscopic classifications as star-forming or passive. We compare the incidence rates of high column density O VI absorption (N O VI ≥ 1014.3 cm-2) near star-forming and passive galaxies in two narrow ranges of stellar mass and, separately, in a matched range of halo mass. In all three mass ranges, the O VI covering fraction within 150 kpc is higher around star-forming galaxies than around passive galaxies with greater than 3σ-equivalent statistical significance. On average, the CGM of star-forming galaxies with M * ~ 3 × 1010 M ⊙ contains more O VI than the CGM of passive galaxies with the same mass. This difference is evidence for a CGM transformation that happens together with galaxy quenching and is not driven primarily by halo mass.

Keywords: circumgalactic medium; extragalactic astronomy; quenched galaxies
A VLBA Survey of Radio Stars in the Orion Nebula Cluster. II. Astrometry

From Very Long Baseline Array (VLBA) observations we previously identified a population of 123 young stellar systems with nonthermal radio emission toward the core of the Orion Nebula Cluster (ONC). We find optical sources in the Gaia DR2 catalog for 34 of them within 0"2 of the radio positions. Most of the radio sources are likely companions of Gaia detections. However, there are 11 stars whose VLBA positions differ from Gaia by <1.6 mas, and some of these radio sources probably are the direct counterparts of the optical stars. We are able to obtain radio proper motions for 23 stars. Combining the stellar proper motions derived from the VLBA and Gaia DR2 data we find the global motion and velocity dispersion of the ONC to be (μα∗, μδ) = (1.20 ± 0.09, 0.18 ± 0.09) mas yr-1 and ( ${\sigma }_{{\mu }_{\alpha }}\ast ,{\sigma }_{{\mu }_{\delta }}$ ) = (0.84 ± 0.09, 1.30 ± 0.09) mas yr-1. Finally, we looked for ordered motions by estimating the means of scalar and vectorial products, which results in $\overline{{\boldsymbol{v}}\cdot \hat{{\boldsymbol{r}}}}=-0.61\pm 1.00$ km s-1 and $\overline{{\boldsymbol{v}}\times \hat{{\boldsymbol{r}}}}=0.57\pm 0.95$ km s-1. These do not show indications that the young stellar cluster is in expansion, contraction, or rotation.

Keywords: star formation; radio astrometry; non-thermal radiation sources
A Novel Survey for Young Substellar Objects with the W-band Filter. VI. Spectroscopic Census of Substellar Members and the IMF of the σ Orionis Cluster

Low-mass stars and substellar objects are essential in tracing the initial mass function (IMF). We study the nearby young σ Orionis cluster (d ~ 408 pc, age ~ 1.8 Myr) using deep near-infrared (NIR) photometric data in the J, W, and H bands from WIRCam on the Canada-France-Hawaii Telescope. We use the water absorption feature to select brown dwarfs photometrically and confirm their nature spectroscopically with IRTF-SpeX. Additionally we select candidate low-mass stars for spectroscopy and analyze their membership and those of literature sources using astrometry from Gaia DR3. We obtain NIR spectra for 28 very-low-mass stars and brown dwarfs and estimate their spectral type between M3 and M8.5 (masses ranging between 0.3 and 0.01 M ⊙). Apart from these, we also identify five new planetary-mass candidates which require further spectroscopic confirmation of youth. We compile a comprehensive catalog of 170 spectroscopically confirmed members in the central region of the cluster, for a wide mass range of ~19-0.004 M ☉. We estimate the star-to-brown-dwarf ratio to be ~4, within the range reported for other nearby star-forming regions. With the updated catalog of members we trace the IMF down to 4 M Jup and we find that a two-segment power law fits the substellar IMF better than a log-normal distribution.

Keywords: brown dwarfs; initial mass function; star forming regions; low mass stars