Sazuna/UAT_keywords huggingface dataset:
Photochemistry of Venus-like Planets Orbiting K- and M-dwarf Stars. Compared to the diversity seen in exoplanets, Venus is a veritable astrophysical twin of the Earth; however, its global cloud layer truncates features in transmission spectroscopy, masking its non-Earth-like nature. Observational indicators that can distinguish an exo-Venus from an exo-Earth must therefore survive above the cloud layer. The above-cloud atmosphere is dominated by photochemistry, which depends on the spectrum of the host star and therefore changes between stellar systems. We explore the systematic changes in photochemistry above the clouds of Venus-like exoplanets orbiting K-dwarf or M-dwarf host stars, using a recently validated model of the full Venus atmosphere (0-115 km) and stellar spectra from the Measurements of the Ultraviolet Spectral Characteristics of Low-mass Exoplanetary Systems (MUSCLES) Treasury survey. SO2, OCS, and H2S are key gas species in Venus-like planets that are not present in Earth-like planets, and could therefore act as observational discriminants if their atmospheric abundances are high enough to be detected. We find that SO2, OCS, and H2S all survive above the cloud layer when irradiated by the coolest K dwarf and all seven M dwarfs, whereas these species are heavily photochemically depleted above the clouds of Venus. The production of sulfuric acid molecules that form the cloud layer decreases for decreasing stellar effective temperature. Less steady-state photochemical oxygen and ozone forms with decreasing stellar effective temperature, and the effect of chlorine-catalyzed reaction cycles diminish in favor of HOx and SOx catalyzed cycles. We conclude that trace sulfur gases will be prime observational indicators of Venus-like exoplanets around M-dwarf host stars, potentially capable of distinguishing an exo-Venus from an exo-Earth.

Keywords: Extrasolar rocky planets, M dwarf stars, Planetary atmospheres, Venus, Exoplanet astronomy, K dwarf stars, Exoplanet atmospheres
High-energy Neutrinos from Magnetized Coronae of Active Galactic Nuclei and Prospects for Identification of Seyfert Galaxies and Quasars in Neutrino Telescopes. Particles may be accelerated in magnetized coronae via magnetic reconnections and/or plasma turbulence, leading to high-energy neutrinos and soft γ-rays. We evaluate the detectability of neutrinos from nearby bright Seyfert galaxies identified by X-ray measurements. In the disk-corona model, we find that NGC 1068 is the most promising Seyfert galaxy in the Northern sky, where IceCube is the most sensitive, and show prospects for the identification of aggregated neutrino signals from Seyfert galaxies bright in X-rays. Moreover, we demonstrate that nearby Seyfert galaxies are promising targets for the next generation of neutrino telescopes such as KM3NeT and IceCube-Gen2. For KM3NeT, Cen A can be the most promising source in the Southern sky if a significant fraction of the observed X-rays come from the corona, and it could be identified in few years of KM3NeT operation. Our results reinforce the idea that hidden cores of supermassive black holes are the dominant sources of the high-energy neutrino emission and underlines the necessity of better sensitivity to medium-energy ranges in future neutrino detectors for identifying the origin of high-energy cosmic neutrinos.

Keywords: AGN host galaxies, Neutrino telescopes, High energy astrophysics, Neutrino astronomy, Active galaxies, Active galactic nuclei, Non-thermal radiation sources, Gamma-rays, Particle astrophysics
Dynamical Splitting of Spot-producing Magnetic Rings in a Nonlinear Shallow-water Model. We explore the fundamental physics of narrow toroidal rings during their nonlinear magnetohydrodynamic evolution at tachocline depths. Using a shallow-water model, we simulate the nonlinear evolution of spot-producing toroidal rings of 6° latitudinal width and a peak field of 15 kG. We find that the rings split; the split time depends on the latitude of each ring. Ring splitting occurs fastest, within a few weeks, at latitudes 20°-25°. Rossby waves work as perturbations to drive the instability of spot-producing toroidal rings; the ring split is caused by the "mixed stress" or cross-correlations of perturbation velocities and magnetic fields, which carry magnetic energy and flux from the ring peak to its shoulders, leading to the ring split. The two split rings migrate away from each other, the high-latitude counterpart slipping poleward faster due to migrating mixed stress and magnetic curvature stress. Broader toroidal bands do not split. Much stronger rings, despite being narrow, do not split due to rigidity from stronger magnetic fields within the ring. Magnetogram analysis indicates the emergence of active regions sometimes at the same longitudes but separated in latitude by 20° or more, which could be evidence of active regions emerging from split rings, which consistently contribute to observed high-latitude excursions of butterfly wings during the ascending, peak, and descending phases of a solar cycle. Observational studies in the future can determine how often new spots are found at higher latitudes than their lower-latitude counterparts and how the combinations influence solar eruptions and space weather events.

Keywords: Solar active region magnetic fields, Magnetohydrodynamics, Space weather
Modeling Grain Rotational Disruption by Radiative Torques and Extinction of Active Galactic Nuclei. Extinction curves observed toward individual Active Galactic Nuclei (AGN) usually show a steep rise toward far-ultraviolet (FUV) wavelengths and can be described by the Small Magellanic Cloud (SMC)-like dust model. This feature suggests the dominance of small dust grains of size a ≤ 0.1 μm in the local environment of AGN, but the origin of such small grains is unclear. In this paper, we aim to explain this observed feature by applying the RAdiative Torque Disruption (RATD) to model the extinction of AGN radiation from FUV to mid-infrared (MIR) wavelengths. We find that in the intense radiation field of AGN, large composite grains of size a ≥ 0.1 μm are significantly disrupted to smaller sizes by RATD up to dRATD &gt; 100 pc in the polar direction and dRATD ~ 10 pc in the torus region. Consequently, optical-MIR extinction decreases, whereas FUV-near-ultraviolet extinction increases, producing a steep far-UV rise extinction curve. The resulting total-to-selective visual extinction ratio thus significantly drops to RV &lt; 3.1 with decreasing distances to AGN center due to the enhancement of small grains. The dependence of RV with the efficiency of RATD will help us to study the dust properties in the AGN environment via photometric observations. In addition, we suggest that the combination of the strength between RATD and other dust destruction mechanisms that are responsible for destroying very small grains of a ≤ 0.05 μm is the key for explaining the dichotomy observed "SMC" and "gray" extinction curve toward many AGN.

Keywords: Astrophysical dust processes, Active galactic nuclei, Interstellar dust extinction
Generation of Short-scale Electrostatic Fields in the Solar Atmosphere and the Role of Helium Ions. Theoretical models are presented to show that expansion of plasma in the radial direction from a denser solar surface to a rarefied upper atmosphere with short-scale inhomogeneous field-aligned flows and currents in the form of thin threads itself is an important source of electrostatic instabilities. Multifluid theory shows that the shear flow-driven purely growing electric fields appear in the transition region. On the other hand, plasma kinetic theory predicts that the short-scale current sheets (or filaments) produce current-driven electrostatic ion acoustic (CDEIA) waves in the hydrogen plasma of the transition region that damp out in the system through wave-particle interactions and increase the temperature. Similar processes take place in the solar corona and act positively for increasing the temperature further and maintaining it. The shear flow-driven instabilities and CDEIA waves have short perpendicular wavelengths of the order of 1 m and low frequencies of the order of 1 or several Hz when the ions' shear flow scale length is considered to be of the order of 1 km. It is pointed out that the purely growing fluid instabilities turn into oscillatory instabilities and the growth rates of kinetic CDEIA wave instabilities are reduced when the dynamics of 10% helium ions is taken into account along with 90% hydrogen ions. Therefore, the role of helium ions should not be ignored in the study of wave dynamics in solar plasma.

Keywords: Solar coronal waves
Spatial and Kinematic Clustering of Stars in the Galactic Disk. The Galactic disk is expected to be spatially and kinematically clustered on many scales due to both star formation and the Galactic potential. In this work we calculate the spatial and kinematic two-point correlation functions (TPCF) using a sample of 1.7 × 106 stars with radial velocities from Gaia DR2. Clustering is detected on spatial scales of 1-300 pc and a velocity scale of 15 km s-1. After removing bound structures, the data have a power-law index of γ ≈ -1 for 1 pc &lt; Δr &lt; 100 pc and γ ≲ -1.5 for Δr &gt; 100 pc. We interpret these results with the aid of a star-by-star simulation of the Galaxy, in which stars are born in clusters orbiting in a realistic potential that includes spiral arms, a bar, and giant molecular clouds. We find that the simulation largely agrees with the observations at most spatial and kinematic scales. In detail, the TPCF in the simulation is shallower than the data at ≲20 pc scales, and steeper than the data at ≳30 pc. We also find a persistent clustering signal in the kinematic TPCF for the data at large Δv (&gt;5 km s-1) that is not present in the simulations. We speculate that this mismatch between observations and simulations may be due to two processes: hierarchical star formation and transient spiral arms. We also predict that the addition of ages and metallicities measured with a precision of 50% and 0.05 dex, respectively, will enhance the clustering signal beyond current measurements.

Keywords: Two-point correlation function, Star formation, Milky Way Galaxy, Star clusters
Radiative Association between Neutral Radicals in the Interstellar Medium: CH<SUB>3</SUB> + CH<SUB>3</SUB>O. Uncertainties in the production mechanisms of interstellar complex organic molecules call for a precise investigation of gas-phase synthetic routes for these molecules, especially at low temperatures. Here, we report a study of the gas-phase formation of dimethyl ether from the neutral radicals methyl and methoxy via the process of radiative association. This process may be important to synthesize dimethyl ether and species such as methyl formate, for which dimethyl ether is a precursor. The reaction is found to be rapid by the standards of radiative association, especially at 10 K, where its rate coefficient is calculated by two different methods to be 3 × 10-11 or 2 × 10-10 cm3 s-1; the lower rate is calculated with a more precise theory and is likely more accurate. Insertion of this reaction into the Nautilus network is found not to explain fully the abundance of dimethyl ether in cold and prestellar cores, especially in those cores with the highest dimethyl ether abundances.

Keywords: Interstellar molecules, Reaction rates, Astrochemistry
In Search of Infall Motion in Molecular Clumps. III. HCO+ (1-0) and H13CO+ (1-0) Mapping Observations toward Confirmed Infall Sources. The study of infall motion helps us to understand the initial stages of star formation. In this paper, we use the IRAM 30 m telescope to make mapping observations of 24 infall sources confirmed in previous work. The lines we use to track gas infall motions are HCO+ (1-0) and H13CO+ (1-0). All 24 sources show HCO+ emissions, while 18 sources show H13CO+ emissions. The HCO+ integrated intensity maps of 17 sources show clear clumpy structures; for the H13CO+ line, 15 sources show clumpy structures. We estimated the column density of HCO+ and H13CO+ using the RADEX radiation transfer code, and the obtained [HCO+]/[H2] and [H13CO+]/[HCO+] of these sources are about 10-11-10-7 and 10-3-1, respectively. Based on the asymmetry of the line profile of the HCO+, we distinguish these sources: 19 sources show blue asymmetric profiles, and the other sources show red profiles or symmetric peak profiles. For eight sources that have double-peaked blue line profiles and signal-to-noise ratios greater than 10, the RATRAN model is used to fit their HCO+ (1-0) lines, and to estimate their infall parameters. The mean V in of these sources is 0.3-1.3 km s-1, and the ${\dot{M}}_{\mathrm{in}}$ is about 10-3-10-4 M ⊙ yr-1, which is consistent with the results of intermediate or massive star formation in previous studies. The V in estimated from the Myers model is 0.1-1.6 km s-1, and the ${\dot{M}}_{\mathrm{in}}$ is within 10-3-10-5 M ⊙ yr-1. In addition, some identified infall sources show other star-forming activities, such as outflows and maser emissions. Especially for those sources with a double-peaked blue asymmetric profile, most of them have both infall and outflow evidence.

Keywords: Star formation, Molecular clouds, Interstellar medium, Collapsing clouds
AGN STORM 2. I. First results: A Change in the Weather of Mrk 817. We present the first results from the ongoing, intensive, multiwavelength monitoring program of the luminous Seyfert 1 galaxy Mrk 817. While this active galactic nucleus was, in part, selected for its historically unobscured nature, we discovered that the X-ray spectrum is highly absorbed, and there are new blueshifted, broad, and narrow UV absorption lines, which suggest that a dust-free, ionized obscurer located at the inner broad-line region partially covers the central source. Despite the obscuration, we measure UV and optical continuum reverberation lags consistent with a centrally illuminated Shakura─Sunyaev thin accretion disk, and measure reverberation lags associated with the optical broad-line region, as expected. However, in the first 55 days of the campaign, when the obscuration was becoming most extreme, we observe a de-coupling of the UV continuum and the UV broad emission-line variability. The correlation recovered in the next 42 days of the campaign, as Mrk 817 entered a less obscured state. The short C IV and Lyα lags suggest that the accretion disk extends beyond the UV broad-line region.

Keywords: Black hole physics
A Sample of Massive Black Holes in Dwarf Galaxies Detected via [Fe X] Coronal Line Emission: Active Galactic Nuclei and/or Tidal Disruption Events. The massive black hole (BH) population in dwarf galaxies (M BH ≲ 105 M ⊙) can provide strong constraints on the origin of BH seeds. However, traditional optical searches for active galactic nuclei (AGNs) only reliably detect high-accretion, relatively high-mass BHs in dwarf galaxies with low amounts of star formation, leaving a large portion of the overall BH population in dwarf galaxies relatively unexplored. Here, we present a sample of 81 dwarf galaxies (M ⋆ ≤ 3 × 109 M ⊙) with detectable [Fe X]λ6374 coronal line emission indicative of accretion onto massive BHs, only two of which were previously identified as optical AGNs. We analyze optical spectroscopy from the Sloan Digital Sky Survey and find [Fe X]λ6374 luminosities in the range L [Fe x] ≈ 1036-1039 erg s-1, with a median value of 1.6 × 1038 erg s-1. The [Fe X] λ6374 luminosities are generally much too high to be produced by stellar sources, including luminous Type IIn supernovae (SNe). Moreover, based on known SNe rates, we expect at most eight Type IIn SNe in our sample. That said, the [Fe X]λ6374 luminosities are consistent with accretion onto massive BHs from AGNs or tidal disruption events (TDEs). We find additional indicators of BH accretion in some cases using other emission line diagnostics, optical variability, and X-ray and radio emission (or some combination of these). However, many of the galaxies in our sample only have evidence for a massive BH based on their [Fe X]λ6374 luminosities. This work highlights the power of coronal line emission to find BHs in dwarf galaxies missed by other selection techniques and to probe the BH population in bluer, lower-mass dwarf galaxies.

Keywords: Black holes, Tidal disruption, Active galaxies, Dwarf galaxies, Low-luminosity active galactic nuclei, Active galactic nuclei
Mechanical Energy Deposition in Cool Star Atmospheres: Resonant Coupling to Coronal Loops in M Dwarfs. The efficiency of coronal heating ɛ(cor) in a star can be quantified by L X/L bol, i.e., the ratio of X-ray luminosity to bolometric luminosity. The efficiency of chromospheric heating in the same star ɛ(chr) is typically assumed to be proportional to L(Hα)/L bol or L(Ca K)/L bol where the lines Hα and Ca K are often the two strongest emission lines in the visible spectrum: the constant of proportionality (η = ɛ(chr)/[L(Hα)/L bol] &gt; 1) includes contributions from many other lines emitted by the chromosphere. In the case of the quiet Sun, it has been known for decades that, in the Sun, the efficiency of chromospheric heating is larger by a factor of ɛ(chr)/ɛ(cor) &gt; 10 than the efficiency of coronal heating. Over the intervening years, data pertaining to ɛ(cor) and ɛ(chr) have been estimated for an increasingly large sample of main-sequence stars with spectral types later than the Sun. These data suggest that among M dwarfs, the efficiency ratio ɛ(chr)/ɛ(cor) may in some stars become smaller than in the solar case. The effect of this is such that the value of ɛ(cor) may become comparable to the value of ɛ(chr). Here, we seek to understand why coronal heating may be &gt;10 times more efficient (relative to chromospheric heating) in certain M dwarfs than in the Sun. Using data on coronal loop properties in flaring stars, we examine the hypothesis that in M dwarfs, the enhanced efficiency of coronal heating may be related to resonant coupling between coronal loops and the source of mechanical energy in the convection zone.

Keywords: Solar coronal heating, Late-type dwarf stars, Stellar coronae
A Catalog of Host Galaxies for WISE-selected AGN: Connecting Host Properties with Nuclear Activity and Identifying Contaminants. We present a catalog of physical properties for galaxies hosting active galactic nuclei (AGN) detected by the Wide-field Infrared Survey Explorer (WISE). By fitting broadband spectral energy distributions of sources in the WISE AGN Catalog with empirical galaxy and AGN templates, we derive photometric redshifts, AGN bolometric luminosities, measures of AGN obscuration, host galaxy stellar masses, and host galaxy star formation rates (SFRs) for 695,273 WISE AGN. The wide-area nature of this catalog significantly augments the known number of obscured AGN out to redshifts z ~ 3 and will be useful for studies focused on AGN or their host galaxy physical properties. We first show that the most likely non-AGN contaminants are galaxies at redshifts z = 0.2-0.3, with relatively blue W1-W2 colors, and with high specific SFRs for which the dust continuum emission is elevated in the W2 filter. Toward increasingly lower redshifts, WISE AGN host galaxies have systematically lower specific SFRs relative to those of normal star-forming galaxies, likely due to decreased cold gas fractions and the time delay between global star formation and AGN triggering. Finally, WISE AGN obscuration is not strongly correlated with AGN bolometric luminosity but shows a significant negative correlation with the Eddington ratio. This result is consistent with a version of the receding torus model in which the obscuring material is located within the supermassive black hole gravitational sphere of influence and the dust inner radius increases due to radiation pressure.

Keywords: AGN host galaxies, Galaxy stellar content, Active galactic nuclei, Dust continuum emission, Spectral energy distribution, Infrared galaxies, Galaxy masses, High-redshift galaxies, Catalogs
GRB 210121A: A Typical Fireball Burst Detected by Two Small Missions. The Chinese CubeSat Mission, Gamma Ray Integrated Detectors (GRID), recently detected its first gamma-ray burst, GRB 210121A, which was jointly observed by the Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM). This burst is confirmed by several other missions, including Fermi and Insight-HXMT. We combined multimission observational data and performed a comprehensive analysis of the burst's temporal and spectral properties. Our results show that the burst is relatively special in its high peak energy, thermal-like low-energy indices, and large fluence. By putting it to the E p -E  γ,iso relation diagram with assumed distance, we found that this burst can be constrained at the redshift range of [0.3, 3.0]. The thermal spectral component is also confirmed by the direct fit of the physical models to the observed spectra. Interestingly, the physical photosphere model also constrained a redshift of z ~ 0.3 for this burst, which helps us to identify a host galaxy candidate at such a distance within the location error box. Assuming that the host galaxy is real, we found that the burst can be best explained by the photosphere emission of a typical fireball with an initial radius of r 0 ~ 3.2 × 107 cm.

Keywords: Gamma-ray bursts
The Obliquity of HIP 67522 b: A 17 Myr Old Transiting Hot, Jupiter-sized Planet. HIP 67522 b is a 17 Myr old, close-in (Porb = 6.96 days), Jupiter-sized (R = 10 R⊕) transiting planet orbiting a Sun-like star in the Sco-Cen OB association. We present our measurement of the system's projected orbital obliquity via two spectroscopic transit observations using the CHIRON spectroscopic facility. We present a global model that accounts for large surface brightness features typical of such young stars during spectroscopic transit observations. With a value of $| \lambda | ={5.8}_{-5.7}^{{+2.8}^\circ} $ it is unlikely that this well-aligned system is the result of a high-eccentricity-driven migration history. By being the youngest planet with a known obliquity, HIP 67522 b holds a special place in contributing to our understanding of giant planet formation and evolution. Our analysis shows the feasibility of such measurements for young and very active stars.

Keywords: Planetary alignment, Exoplanet systems, Exoplanet astronomy, Radial velocity, Transit photometry, Planet formation
First Doppler Limits on Binary Planets and Exomoons in the HR 8799 System. We place the first constraints on binary planets and exomoons from Doppler monitoring of directly imaged exoplanets. We model radial velocity observations of HR 8799 b, c, and d from Ruffio et al. and determine upper limits on the $m\sin i$ of short-period binary planets and satellites. At 95% confidence, we rule out companions orbiting the three planets more massive than $m\sin i=2$ MJ with orbital periods shorter than 5 days. We achieve our tightest constraints on moons orbiting HR 8799c, where with 95% confidence we rule out out edge-on Jupiter-mass companions in periods shorter than 5 days and edge-on half-Jupiter-mass moons in periods shorter than 1 day. These radial velocity observations come from spectra with resolution 20 times lower than typical radial velocity instruments and were taken using a spectrograph that was designed before the first directly imaged exoplanet was discovered. Similar data sets from new and upcoming instruments will probe significantly lower exomoon masses.

Keywords: Exoplanet detection methods, Natural satellites (Extrasolar), Direct imaging