Sazuna/UAT_keywords huggingface dataset:
A Hidden Friend for the Galactic Center Black Hole, Sgr A*. The hierarchical nature of galaxy formation suggests that a supermassive black hole binary could exist in our galactic center. We propose a new approach to constraining the possible orbital configuration of such a binary companion to the galactic center black hole Sagittarius A* (Sgr A*) through the measurement of stellar orbits. Focusing on the star S0-2, we show that requiring its orbital stability in the presence of a companion to Sgr A* yields stringent constraints on the possible configurations of such a companion. Furthermore, we show that precise measurements of time variations in the orbital parameters of S0-2 could yield stronger constraints. Using existing data on S0-2 we derive upper limits on the binary black hole separation as a function of the companion mass. For the case of a circular orbit, we can rule out a 105 M ⊙ companion with a semimajor axis greater than 170 au or 0.8 mpc. This is already more stringent than bounds obtained from studies of the proper motion of Sgr A*. Including other stars orbiting the galactic center should yield stronger constraints that could help uncover the presence of a companion to Sgr A*. We show that a companion can also affect the accretion process, resulting in a variability that may be consistent with the measured infrared flaring timescales and amplitudes. Finally, if such a companion exists, it will emit gravitational wave radiation, potentially detectable with the Laser Interferometer Space Antenna (LISA).

Keywords: Supermassive black holes, Galactic center, Gravitation, Milky Way dynamics, Gravitational wave sources, Milky Way Galaxy physics, Gravitational waves, Milky Way Galaxy, Astrophysical black holes
The Chemical Signatures of Planetary Engulfment Events in Binary Systems. Planetary engulfment events involve the chemical assimilation of a planet into a star’s external layer. This can cause a change in the chemical pattern of the stellar atmosphere in a way that mirrors the composition of the rocky object engulfed, with the refractory elements being more abundant than the volatiles. Due to these stellar chemical changes, planetary engulfment events can render the process of chemical tagging potentially inaccurate. A line-by-line differential analysis of twin stars in wide binary systems allows us to test the chemical homogeneity of these associations with typical individual stellar Fe I uncertainties of 0.01 dex and eventually unveil chemical anomalies that could be attributed to planetary engulfment events. Out of the 14 systems analyzed here, we report the discovery of the most chemically inhomogeneous system to date (HIP 34407/HIP 34426). The median difference in abundances of refractory elements within the pair is 0.19 dex and the trend between the differential abundances and condensation temperature suggests that the anomaly is likely due to a planetary engulfment event. Within our sample, five other chemically anomalous systems are found.

Keywords: Exoplanets, Stellar abundances, Chemical abundances, Wide binary stars, Chemically peculiar stars
On the Rate of Neutron Star Binary Mergers from Globular Clusters. The first detection of gravitational waves from a neutron star-neutron star (NS-NS) merger, GW170817, and the increasing number of observations of short gamma-ray bursts have greatly motivated studies of the origins of NS-NS and neutron star-black hole (NS-BH) binaries. We calculate the merger rates of NS-NS and NS-BH binaries from globular clusters (GCs) using realistic GC simulations with the CMC Cluster Catalog. We use a large sample of models with a range of initial numbers of stars, metallicities, virial radii, and galactocentric distances, representative of the present-day Milky Way GCs, to quantify the inspiral times and volumetric merger rates as a function of redshift, both inside and ejected from clusters. We find that over the complete lifetime of most GCs, stellar BHs dominate the cluster cores and prevent the mass segregation of NSs, thereby reducing the dynamical interaction rates of NSs so that at most a few NS binary mergers are ever produced. We estimate the merger rate in the local universe to be ∼0.02 Gpc-3 yr-1 for both NS-NS and NS-BH binaries, or a total of ∼0.04 Gpc-3 yr-1 for both populations. These rates are about 5 orders of magnitude below the current empirical merger rate from the Laser Interferometer Gravitational-Wave Observatory/Virgo. We conclude that dynamical interactions in GCs do not play a significant role in enhancing the NS-NS and NS-BH merger rates.

Keywords: Globular star clusters, Neutron stars, Computational methods, Stellar dynamics
The MOSDEF Survey: [S III] as a New Probe of Evolving Interstellar Medium Conditions. We present measurements of [S III]λλ9069,9531 for a sample of z ∼ 1.5 star-forming galaxies, the first representative sample with measurements of these lines at z ≳ 0.1. We employ the line ratio S 32 ≡ [S III]λλ9069,9531/[S II]λλ6716,6731 as a novel probe of evolving interstellar medium (ISM) conditions. Since this ratio includes the low-ionization line [S II], it is crucial that the effects of diffuse ionized gas (DIG) on emission-line ratios be accounted for in z ∼ 0 galaxy spectra, or else that comparisons be made to samples of local H II regions in which DIG emission is not present. We find that S 32 decreases with increasing stellar mass at both z ∼ 1.5 and z ∼ 0, but with a shallow slope suggesting S 32 has a weak dependence on metallicity, in contrast with [O III]/[O II] that displays a strong metallicity dependence. As a result, S 32 only mildly evolves with redshift at fixed stellar mass. The z ∼ 1.5 sample is systematically offset toward lower S 32 and higher [S II]/Hα at fixed [O III]/Hβ relative to z = 0 H II regions. We find that such trends can be explained by a scenario in which the ionizing spectrum is harder at fixed O/H with increasing redshift, but are inconsistent with an increase in ionization parameter at fixed O/H. This analysis demonstrates the advantages of expanding beyond the strongest rest-optical lines for evolutionary studies, and the particular utility of [S III] for characterizing evolving ISM conditions and stellar compositions. These measurements provide a basis for estimating [S III] line strengths for high-redshift galaxies, a line that the James Webb Space Telescope will measure out to z ∼ 5.5. Based on data obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA, and was made possible by the generous financial support of the W.M. Keck Foundation.

Keywords: High-redshift galaxies, Galaxy evolution, Interstellar medium
Effects of Close Binary Evolution on the Main-sequence Morphology of Young Star Clusters. Star clusters are the building blocks of galaxies. They are composed of stars of nearly equal age and chemical composition, allowing us to use them as chronometers and as testbeds for gauging stellar evolution. It has become clear recently that massive stars are formed preferentially in close binaries, in which mass transfer will drastically change the evolution of the stars. This is expected to leave a significant imprint in the distribution of cluster stars in the Hertzsprung-Russell diagram. Our results, based on a dense model grid of more than 50,000 detailed binary-evolution calculations, show several distinct, coeval main-sequence (MS) components, most notably an extended MS turnoff region, and a group of near-critical rotating stars that is spread over a large luminosity range on the red side of the classical MS. We comprehensively demonstrate the time evolution of the features in an animation, and we derive analytic expressions to describe these features. We find quantitative agreement with results based on recent photometric and spectroscopic observations. We conclude that while other factors may also be at play, binary evolution has a major impact on the MS morphology of young star clusters.

Keywords: Close binary stars, Stellar evolutionary models, Interacting binary stars, Stellar evolution
Detection of Ionized Calcium in the Atmosphere of the Ultra-hot Jupiter KELT-9b. With a dayside temperature in excess of 4500 K, comparable to a mid-K-type star, KELT-9b is the hottest planet known. Its extreme temperature makes KELT-9b a particularly interesting test bed for investigating the nature and diversity of gas giant planets. We observed the transit of KELT-9b at high spectral resolution (R ∼ 94,600) with the CARMENES instrument on the Calar Alto 3.5 m telescope. Using these data, we detect for the first time ionized calcium (Ca II triplet) absorption in the atmosphere of KELT-9b; this is the second time that Ca II has been observed in a hot Jupiter. Our observations also reveal prominent Hα absorption, confirming the presence of an extended hydrogen envelope around KELT-9b. We compare our detections with an atmospheric model and find that all four lines form between atmospheric temperatures of 6100 and 8000 K and that the Ca II lines form at pressures between 50 and 100 nbar while the Hα line forms at a lower pressure (∼10 nbar), higher up in the atmosphere. The altitude that the core of Hα line forms is found to be ∼1.4 R  p , well within the planetary Roche lobe (∼1.9 R  p ). Therefore, rather than probing the escaping upper atmosphere directly, the Hα line and the other observed Balmer and metal lines serve as atmospheric thermometers enabling us to probe the planet’s temperature profile, thus the energy budget.

Keywords: Exoplanet atmospheric composition , Hot Jupiters, Exoplanets, Planetary atmospheres, Extrasolar gaseous giant planets, Exoplanet atmospheres
On Post-starburst Galaxies Dominating Tidal Disruption Events. A starburst induced by a galaxy merger may create a relatively thin central stellar disk at radius ≤100 pc. We calculate the rate of tidal disruption events (TDEs) by the inspiraling secondary supermassive black hole (SMBH) through the disk. With a small enough stellar velocity dispersion (σ /{V}c≤slant 0.1) in the disk, it is shown that 105-106 TDEs of solar-type main-sequence stars per post-starburst galaxy (PSB) can be produced to explain their dominance in producing observed TDEs. Although the time it takes to bring the secondary SMBH to the disk apparently varies in the range of ∼0.1-1 Gyr since the starburst, depending on its landing location and subsequently due to dynamical friction with stars exterior to the central stellar disk in question, the vast majority of TDEs by the secondary SMBH in any individual PSB occur within a time span shorter than ∼30 Myr. Five unique testable predictions of this model are suggested.

Keywords: Supermassive black holes, Galaxy stellar disks, Tidal disruption, Galaxy mergers, Dynamical friction
Evidence for H2 Dissociation and Recombination Heat Transport in the Atmosphere of KELT-9b. Phase curve observations provide an opportunity to study the energy budgets of exoplanets by quantifying the amount of heat redistributed from their daysides to their nightsides. Theories of phase curves for hot Jupiters have focused on the balance between radiation and dynamics as the primary parameter controlling heat redistribution. However, recent phase curves have shown deviations from the trends that emerge from this theory, which has led to work on additional processes that may affect hot Jupiter energy budgets. One such process, molecular hydrogen dissociation and recombination, can enhance energy redistribution on ultra-hot Jupiters with temperatures above ∼2000 K. In order to study the impact of H2 dissociation on ultra-hot Jupiters, we present a phase curve of KELT-9b observed with the Spitzer Space Telescope at 4.5 μm. KELT-9b is the hottest known transiting planet, with a 4.5 μm dayside brightness temperature of {4566}-136+140 {{K}} and a nightside temperature of {2556}-97+101 {{K}}. We observe a phase curve amplitude of 0.609 ± 0.020 and an offset of {18.7}-2.3+2.1^\circ . The observed amplitude is too small to be explained by a simple balance between radiation and advection. General circulation models (GCMs) and an energy balance model that include the effects of H2 dissociation and recombination provide a better match to the data. The GCMs, however, predict a maximum phase offset of 5°, which disagrees with our observations at &gt;5σ confidence. This discrepancy may be due to magnetic effects in the planet’s highly ionized atmosphere.

Keywords: Exoplanet atmospheres, Hot Jupiters
Relationship between Current Filaments and Turbulence During a Turbulent Reconnection. Both magnetic reconnection and turbulence can play crucial roles in space plasmas. The current layers, developing during magnetic reconnection, can collapse into various small-scale coherent structures, such as current filaments. These current filaments can significantly modulate the kinetic-scale turbulence. However, the quantitative correlation between the current filaments and turbulence remains unknown so far. In this study, we statistically analyze such a relation during a turbulent reconnection in the magnetotail. We find that the kinetic-scale turbulence has a good correlation with the current-density variation ≤ft({J}{\prime }=≤ft|\tfrac{{dJ}}{{dt}}\right|\right). Specifically, (1) the slope of the kinetic-scale power spectral density (PSD), denoted as S PSD, decreases with J‧, exhibiting an empirical relation S PSD = -0.54ln(J‧) - 1.36; (2) the correlation between turbulence intensity (PSD) and J‧ is best at the frequency range 0.02-0.32 ω ce (electron cyclotron frequency); (3) the turbulence intensity (PSD) increases with J‧, exhibiting an empirical relation PSD = J‧ k  • e  b ; and (4) the k of these fitting functions roughly decreases with frequency. These results can advance our understanding of the interplay between magnetic reconnection and turbulence.

Keywords: Interplanetary turbulence, Space plasmas, Plasma jets
In Situ Observations of the Formation of Periodic Collisionless Plasma Shocks from Fast Mode Waves. It has been long theorized, but not directly observed, that low-frequency magnetosonic plasma waves can steepen and form shocks. We show an example of small-amplitude, sinusoidal magnetosonic waves at the proton gyrofrequency upstream of the Martian bow shock. We hypothesize that these waves are produced by an ion beam instability associated with the ionization of hydrogen atoms by charge exchange with solar wind protons, solar photoionization, and/or electron impact ionization. As the waves are convected toward the planet by solar wind flow, the wave amplitude grows due to additional free energy put into the system by further ion beam particles. Finally, the steepened waves form shocks. Because of their development, the shocks are periodic with the separation at the proton gyroperiod. These observations lead to the conclusion that newborn ions may play a crucial role in the formation process of some collisionless plasma shocks in astrophysical and space plasmas.

Keywords: Shocks, Plasma physics, Pickup ions
Discovery of Millisecond Pulsars in the Globular Cluster Omega Centauri. The globular cluster Omega Centauri is the most massive and luminous cluster in the Galaxy. The γ-ray source FL8Y J1326.7-4729 is coincident with the core of the cluster, leading to speculation that hitherto unknown radio pulsars or annihilating dark matter may be present in the cluster core. Here we report on the discovery of five millisecond pulsars (MSPs) in Omega Centauri following observations with the Parkes radio telescope. Four of these pulsars are isolated with spin periods of 4.1, 4.2, 4.6, and 6.8 ms. The fifth has a spin period of 4.8 ms and is in an eclipsing binary system with an orbital period of 2.1 hr. Deep radio continuum images of the cluster center with the Australian Telescope Compact Array reveal a small population of compact radio sources, making it likely that other pulsars await discovery. We consider it highly likely that the MSPs are the source of the γ-ray emission. The long-term timing of these pulsars opens up opportunities to explore the dynamics and interstellar medium of the cluster.

Keywords: Neutron stars, Millisecond pulsars, Globular star clusters, Radio pulsars
Improved Infrared Photometry and a Preliminary Parallax Measurement for the Extremely Cold Brown Dwarf CWISEP J144606.62-231717.8. We present follow-up Spitzer observations at 3.6 μm (ch1) and 4.5 μm (ch2) of CWISEP J144606.62-231717.8, one of the coldest known brown dwarfs in the solar neighborhood. This object was found by mining the Wide-field Infrared Survey Explorer (WISE) and NEOWISE data via the CatWISE Preliminary Catalog by Meisner et al., where an initial Spitzer color of ch1-ch2 = 3.71 ± 0.44 mag was reported, implying it could be one of the reddest, and hence coldest, known brown dwarfs. Additional Spitzer data presented here allows us to revise its color to ch1-ch2 = 2.986 ± 0.048 mag, which makes CWISEP J144606.62-231717.8 the fifth reddest brown dwarf ever observed. A preliminary trigonometric parallax measurement, based on a combination of WISE and Spitzer astrometry, places this object at a distance of {10.1}-1.3+1.7 pc. Based on our improved Spitzer color and preliminary parallax, CWISEP J144606.62-231717.8 has a T eff in the 310-360 K range. Assuming an age of 0.5-13 Gyr, this corresponds to a mass between 2 and 20 M Jup.

Keywords: Trigonometric parallax, Brown dwarfs, Y dwarfs, Solar neighborhood, Proper motions
Clouds will Likely Prevent the Detection of Water Vapor in JWST Transmission Spectra of Terrestrial Exoplanets. We are on the verge of characterizing the atmospheres of terrestrial exoplanets in the habitable zones of M dwarf stars. Due to their large planet-to-star radius ratios and higher frequency of transits, terrestrial exoplanets orbiting M dwarf stars are favorable for transmission spectroscopy. In this work, we quantify the effect that water clouds have on the amplitude of water vapor transmission spectral features of terrestrial exoplanets orbiting M dwarf stars. To do so, we make synthetic transmission spectra from general circulation model (GCM) experiments of tidally locked planets. We improve upon previous work by considering how varying a broad range of planetary parameters affects transmission spectra. We find that clouds lead to a 10-100 times increase in the number of transits required to detect water features with the James Webb Space Telescope (JWST) with varying rotation period, incident stellar flux, surface pressure, planetary radius, and surface gravity. We also find that there is a strong increase in the dayside cloud coverage in our GCM simulations with rotation periods ≳12 days for planets with Earth’s radius. This increase in cloud coverage leads to even stronger muting of spectral features for slowly rotating exoplanets orbiting M dwarf stars. We predict that it will be extremely challenging to detect water transmission features in the atmospheres of terrestrial exoplanets in the habitable zone of M dwarf stars with JWST. However, species that are well-mixed above the cloud deck (e.g., CO2 and CH4) may still be detectable on these planets with JWST.

Keywords: Extrasolar rocky planets, Exoplanet atmospheric composition , Water vapor, Planetary atmospheres, Habitable planets, Exoplanet atmospheres
Is π Men c’s Atmosphere Hydrogen-dominated? Insights from a Non-detection of H I Lyα Absorption. Constraining the composition of super-Earth-to-sub-Neptune-sized planets is a priority in order to understand the processes of planetary formation and evolution. π Men c represents a unique target for the atmospheric and compositional characterization of such planets because it is strongly irradiated and its bulk density is consistent with abundant H2O. We searched for hydrogen from photodissociating H2/H2O in π Men c's upper atmosphere through H I Lyα transmission spectroscopy with the Hubble Space Telescope’s Space Telescope Imaging Spectrograph, but did not detect it. We set 1σ (3σ) upper limits for the effective planet-to-star size ratio R Lyα /R ⋆ = 0.13 (0.24) and 0.12 (0.20) at velocities [-215, -91] km s-1 and [+57, +180] km s-1, respectively. We reconstructed the stellar spectrum, and estimate that π Men c receives about 1350 erg cm-2 s-1 of 5-912 Å energy, enough to cause rapid atmospheric escape. An interesting scenario to explain the non-detection is that π Men c's atmosphere is dominated by H2O or other heavy molecules rather than H2/He. According to our models, abundant oxygen results in less extended atmospheres, which transition from neutral to ionized hydrogen closer to the planet. We compare our non-detection to other detection attempts, and tentatively identify two behaviors: planets with densities ≲2 g cm-3 (and likely hydrogen-dominated atmospheres) result in H I Lyα absorption, whereas planets with densities ≳3 g cm-3 (and plausibly non-hydrogen-dominated atmospheres) do not result in measurable absorption. Investigating a sample of strongly irradiated sub-Neptunes may provide some statistical confirmation if it is shown that they do not generally develop extended atmospheres.

Keywords: Ultraviolet astronomy, Exoplanet atmospheric composition , Aeronomy, Exoplanet atmospheres
The Pitch-angle Distributions of Suprathermal Ions near an Interplanetary Shock. We present a case study of the pitch-angle distributions (PADs) of suprathermal H+, He2+ at ∼10-40 keV/nuc and He+ at ∼8-20 keV/nuc near a reverse shock of a stream interaction region observed by the Plasma and Suprathermal Ion Composition instrument on board the Solar Terrestrial Relations Observatory Ahead spacecraft on 2008 March 9. We find that in both the downstream and upstream region close to the shock, the shocked particles of all three species appear to have a power-law-like spectrum at these suprathermal energies. The PADs of these three species show very similar behavior: in the downstream region, the phase space density appears to be significantly higher in the direction perpendicular to the interplanetary magnetic field (IMF) than in the parallel direction, along which particles accelerated at the shock front are supposed to escape into the downstream region. In the upstream region, the PADs of all three species show a clear beam in the direction antiparallel to the IMF due to the escaping particles from the shock into the upstream region. In addition, we find that suprathermal He+ shows a signature of bidirectional beams in the upstream region very close to the shock. These results suggest that H+, He2+ at ∼10-40 keV/nuc and He+ at ∼8-20 keV/nuc could be accelerated similarly at interplanetary shocks and that shock drift acceleration likely plays an important role in the in situ acceleration of low-energy suprathermal ions.

Keywords: Solar wind, Interplanetary particle acceleration, Interplanetary shocks, Corotating streams