Sazuna/UAT_keywords huggingface dataset:
Energetic Ion Dynamics Near the Cusp Region of Mercury. Energetic ions in Mercury's magnetosphere are very dynamic, similar to those in the magnetosphere of Earth. In this study, we present two energetic proton observations by MErcury Surface, Space ENvironment, GEochemistry and Ranging near the cusp region of Mercury. For one case, we have observed a large flux of energetic protons while the other case has almost no flux, indicating that the near-cusp region may trap energetic particles under particular conditions. In order to understand under what conditions the near-cusp region of Mercury could trap energetic particles, we have used test particle simulations to trace the trajectories of single particles of different energies and pitch angles with a magnetic field model, KT17, that could closely represent the observed in situ magnetic field. Under different magnetic field geometries, the motions of single particles with various energies and pitch angles are different. The test particles can be trapped around the cusp region when the solar disturbance activity that generates the magnetic field local minimum near the cusp region is strong, while the particles cannot be trapped and escape along the magnetic field through the dawnside cusp when there is little solar activity.

Keywords: Mercury (planet), Planetary magnetospheres, Space plasmas, Plasma physics
DFT Study on Interstellar PAH Molecules with Aliphatic Side Groups. Polycyclic aromatic hydrocarbon (PAH) molecules have been long adjudged to contribute to the frequently detected distinct emission features at 3.3, 6.2, 7.7, 8.6, 11.2, and 12.7 μm with weaker and blended features distributed in the 3-20 μm region. The comparatively weaker 3.4 μm emission feature has been attributed to have an aliphatic origin as carrier. PAH with an aliphatic functional group attached to it is one of the proposed potential candidate carriers for the 3.4 μm emission band, however, the assignment of carrier is still enigmatic. In this work, we employ density functional theory calculation on a symmetric and compact PAH molecule; coronene (C24H12) with aliphatic side group to investigate any spectral similarities with observed features at 3-4 μm. The side groups considered in this study are -H (hydrogenated), -CH3 (methyl), -CH2-CH3 (ethyl), and -CH=CH2 (vinyl) functional groups. Considering the possible presence of deuterium (D) in PAHs, we also include D in the aliphatic side group to study the spectral behavior. We present a detailed analysis of the IR spectra of these molecules and discuss possible astrophysical implications.

Keywords: Interstellar molecules, Interstellar dust extinction, Astrochemistry, Infrared astronomy, Interstellar medium
Magnetohydrodynamic Modeling of the Solar Wind Key Parameters and Current Sheets in the Heliosphere: Radial and Solar Cycle Evolution. We develop an axisymmetric numerical MHD model that allows us to investigate the spatial characteristics of the interplanetary magnetic field (IMF) and key solar wind plasma parameters from 20 to 400 solar radii over all heliolatitudes. The study is aimed at an analysis of the evolution of the spatial structure of the heliosphere through the solar cycle. We consider various combinations of the relative input of the quadrupole and dipole harmonics of the solar magnetic field to imitate the solar cycle. Self-consistent solutions for the IMF, electric current, solar wind speed, density, thermal pressure, and temperature in the solar wind are obtained. The spatial evolution of the IMF and properties of quasi-stationary current sheets (QCSs) are analyzed during different phases of the solar cycle. It is shown that a classic low-latitude heliospheric current sheet is formed in the solar wind as a part of the system of longitudinal and latitudinal electric currents symmetric in the northern and southern hemispheres only during solar minimum. While the quadrupole magnetic field increases, the second QCS appears. The model successfully describes a smooth transition from the state of the fast solar wind at high heliolatitudes and the slow solar wind at low heliolatitudes at solar minimum to the solar wind speed of the same values in a wide range of heliolatitudes at solar maximum. It reproduces the actively debated phenomenon of the south-north asymmetry of the IMF in the heliosphere and shows the distribution of thermal plasma parameters consistent with observations.

Keywords: Magnetohydrodynamics, Heliosphere, Solar wind, Solar magnetic fields, Solar activity
Explosions Driven by the Coalescence of a Compact Object with the Core of a Massive-star Companion inside a Common Envelope: Circumstellar Properties, Light Curves, and Population Statistics. We model explosions driven by the coalescence of a black hole or neutron star with the core of its massive-star companion. Upon entering a common-envelope phase, a compact object may spiral all the way to the core. The concurrent release of energy is likely to be deposited into the surrounding common envelope, powering a merger-driven explosion. We use hydrodynamic models of binary coalescence to model the common-envelope density distribution at the time of coalescence. We find toroidal profiles of material, concentrated in the binary's equatorial plane and extending to many times the massive star's original radius. We use the spherically averaged properties of this circumstellar material (CSM) to estimate the emergent light curves that result from the interaction between the blast wave and the CSM. We find that typical merger-driven explosions are brightened by up to three magnitudes by CSM interaction. From population synthesis models, we discover that the brightest merger-driven explosions, MV ∼ -18 to -20, are those involving black holes because they have the most massive and extended CSM. Black hole coalescence events are also common; they represent about 50% of all merger-driven explosions and approximately 0.25% of the core-collapse rate. Merger-driven explosions offer a window into the highly uncertain physics of common-envelope interactions in binary systems by probing the properties of systems that merge rather than eject their envelopes.

Keywords: Close binary stars, Astronomical simulations, Stellar evolution
Spin-polarized Neutron Matter, the Maximum Mass of Neutron Stars, and GW170817. We investigate how a phase transition from neutron-star matter to spin-polarized neutron matter affects the equation of state and mass-radius relation of neutron stars. While general extension schemes for the equation of state allow for high pressures inside neutron stars, we find that a phase transition to spin-polarized neutron matter excludes extreme regimes. Hence, such a transition limits the maximum mass of neutron stars that lie below 2.6-2.9 M⊙, depending on the microscopic nuclear forces used, while significantly larger masses could be reached without these constraints. These limits are in good agreement with recent constraints extracted from the neutron-star merger GW170817 and its electromagnetic counterpart. Assuming the description in terms of spin-polarized neutron matter to be valid in the center of neutron stars, we find that stars with a large spin-polarized domain in their core are ruled out by GW170817.

Keywords: Neutron stars, Nuclear astrophysics, Neutron star cores
ASASSN-16oh: A Nova Outburst with No Mass Ejection—A New Type of Supersoft X-Ray Source in Old Populations. ASASSN-16oh is a peculiar transient supersoft X-ray source without a mass-ejection signature in the field of the Small Magellanic Cloud. Maccarone et al. concluded that ASASSN-16oh is the first dwarf nova with supersoft X-ray that originated from an equatorial accretion belt on a white dwarf (WD). Hillman et al. proposed a thermonuclear runaway model that both the X-rays and V/I photons are emitted from the hot WD. We propose a nova model induced by a high rate of mass accretion during a dwarf nova outburst, I.e., the X-rays originate from the surface of the hydrogen-burning WD whereas the V/I photons are from the irradiated disk. Our model explains the main observational properties of ASASSN-16oh. We also obtained thermonuclear runaway models with no mass ejection for a wide range of parameters of the WD mass and mass-accretion rates including both natural and forced novae in low-metal environments of Z = 0.001 and Z = 0.0001. They are a new type of periodic supersoft X-ray sources with no mass ejection and also a bright transient in V/I bands if they have a large disk. We suggest that such objects are candidates for Type Ia supernova progenitors because its mass is increasing at a very high efficiency (∼100%).

Keywords: Population II stars, Dwarf novae, Novae
Exploring the Mass Segregation Effect of X-Ray Sources in Globular Clusters. III. Signs of Binary Disruption in M28. Using archival Chandra observations with a total effective exposure of 323 ks, we derive an updated catalog of point sources in the bulge globular cluster M28. The catalog contains 502 X-ray sources within an area of ∼475 arcmin2, and more than 90% of these sources are first detected in this cluster. We find significant dips in the radial distribution profiles of X-ray sources in M28, and the projected distance and width of the distribution dip for bright (LX ≳ 4.5 × 1030 erg s-1) X-ray sources are larger than for faint (LX ≲ 4.5 × 1030 erg s-1) sources. Fitting with the "generalized King model" gives a slightly larger average mass for the bright sources (1.30 ± 0.15 M⊙) than for the faint ones (1.09 ± 0.14 M⊙), which supports a universal delay in mass segregation between heavy objects in globular clusters. We show that the dynamical age of M28 is comparable to that of Terzan 5 and much smaller than that of 47 Tuc, but M28 is evolving faster (I.e., with a shorter two-body relaxation timescale) than 47 Tuc. These features may suggest an acceleration effect of cluster dynamical evolution by tidal shock in M28. Besides, we find an abnormal deficiency of X-ray sources in the central region (R ≲ 1'5) of M28 compared with its outskirts, which indicates that M28 may have suffered an early phase of primordial binary disruption within its central region, and the mass segregation effect will erase such a phenomenon as clusters evolve to an older dynamical age.

Keywords: Globular star clusters, X-ray binary stars, Tidal disruption, Stellar dynamics, Dynamical friction
The Evolving AGN Duty Cycle in Galaxies Since z ∼ 3 as Encoded in the X-Ray Luminosity Function. We present a new modeling of the X-ray luminosity function (XLF) of active galactic nuclei (AGNs) out to z ∼ 3, dissecting the contributions of main-sequence (MS) and starburst (SB) galaxies. For each galaxy population, we convolved the observed galaxy stellar mass (M⋆) function with a grid of M⋆-independent Eddington ratio (λEDD) distributions, normalized via empirical black hole accretion rate (BHAR) to star formation rate (SFR) relations. Our simple approach yields an excellent agreement with the observed XLF since z ∼ 3. We find that the redshift evolution of the observed XLF can only be reproduced through an intrinsic flattening of the λEDD distribution and with a positive shift of the break λ*, consistent with an antihierarchical behavior. The AGN accretion history is predominantly made by massive (1010 &lt; M⋆ &lt; 1011 M⊙) MS galaxies, while SB-driven BH accretion, possibly associated with galaxy mergers, becomes dominant only in bright quasars, at log(LX/erg s-1) &gt; 44.36 + 1.28 × (1 + z). We infer that the probability of finding highly accreting (λEDD &gt; 10%) AGNs significantly increases with redshift, from 0.4% (3.0%) at z = 0.5%-6.5% (15.3%) at z = 3 for MS (SB) galaxies, implying a longer AGN duty cycle in the early universe. Our results strongly favor a M⋆-dependent ratio between BHAR and SFR, as BHAR/SFR ∝ M\star0.73[+0.22,-0.29], supporting a nonlinear BH buildup relative to the host. Finally, this framework opens potential questions on super-Eddington BH accretion and different λEDD prescriptions for understanding the cosmic BH mass assembly.

Keywords: AGN host galaxies, Starburst galaxies, Active galaxies, Active galactic nuclei, Galaxy evolution
A More Efficient Search for H<SUB>2</SUB>O Megamaser Galaxies: The Power of X-Ray and Mid-infrared Photometry. We present an investigation of the dependence of H2O maser detection rates and properties on the mid-IR active galactic nucleus (AGN) luminosity, LAGN, and the obscuring column density, NH, based on mid-IR and hard X-ray photometry. Based on spectral energy distribution fitting that allows for decomposition of the black hole accretion and star formation components in the mid-infrared, we show that the megamaser (disk maser) detection rate increases sharply for galaxies with 12 μm AGN luminosity L12 μmAGN greater than 1042 erg s-1, from ≲3% (≲2%) to ∼12% (∼5%). By using the ratio of the observed X-ray to mid-IR AGN luminosity as an indicator of NH, we also find that megamaser (disk maser) detection rates are boosted to 15% (7%) and 20% (9%) for galaxies with NH ≥ 1023 cm-2 and NH ≥ 1024 cm-2, respectively. Combining these column density cuts with a constraint for high L12 μmAGN (≥1042 erg s-1) predicts further increases in the megamaser (disk maser) detection rates to 19% (8%) and 27% (14%), revealing unprecedented potential increases of the megamaser and disk maser detection rates by a factor of 7-15 relative to the current rates, depending on the chosen sample selection criteria. A noteworthy aspect of these new predictions is that the completeness rates are only compromised mildly, with the rates remaining at the level of ∼95%(∼50%) for sources with NH ≥ 1023 cm-2 (NH ≥ 1024 cm-2). Applying these selection methods to current X-ray AGN surveys predicts the detection of ≳15 new megamaser disks.

Keywords: Surveys, Active galaxies, Megamasers, Active galactic nuclei, Astrophysical masers, X-ray active galactic nuclei, X-ray surveys, Broad band photometry, Infrared photometry
Newly Improved Ionization Corrections for the Neutral Interstellar Medium: Enabling Accurate Abundance Determinations in Star-forming Galaxies throughout the Universe. Studies measuring the chemical abundances of the neutral gas in star-forming galaxies (SFGs) require ionization correction factors (ICFs) to accurately measure their metal contents. In the work presented here, we calculate newly improved ICFs for a sample of SFGs. These new corrections include both the contaminating ionized gas along the line of sight (ICFionized) and unaccounted for higher ionization stages in the neutral gas (ICFneutral). We make use of recently acquired spectroscopic observations taken with the Cosmic Origins Spectrograph on board Hubble to measure column densities for Fe II and Fe III. Using the Fe III/Fe II ratios as well as other physical properties (I.e., log[LUV], N(H I), T, and Z), we generate ad hoc photoionization models with CLOUDY to quantify the corrections required for each of the targets. We identify a luminosity threshold of log[LUV] ∼ 40.75 erg s-1 above which the ICFneutral values for nitrogen are relatively higher (ICFneutral=0.05-0.7) than those for the rest of the elements (ICFneutral ∼ 0.01). This behavior indicates that, for the high UV luminosity objects, N II is found in non-negligible quantities in the neutral gas, making these ICFneutral corrections critical for determining the true abundances in the interstellar medium. In addition, we calculate ICFs from a uniform grid of models covering a wide range of physical properties typically observed in studies of SFGs and extragalactic H II regions. We provide the community with tabulated ICF values for the neutral gas abundances measured from a variety of environments and applicable to chemical studies of the high-redshift universe.

Keywords: Starburst galaxies, Chemical abundances, Interstellar medium
A Deep View into the Nucleus of the Sagittarius Dwarf Spheroidal Galaxy with MUSE. II. Kinematic Characterization of the Stellar Populations. The Sagittarius dwarf spheroidal galaxy is in an advanced stage of disruption but still hosts its nuclear star cluster (NSC), M54, at its center. In this paper, we present a detailed kinematic characterization of the three stellar populations present in M54: young metal-rich (YMR); intermediate-age metal-rich (IMR); and old metal-poor (OMP), based on the spectra of ∼6500 individual M54 member stars extracted from a large Multi-Unit Spectroscopic Explorer (MUSE)/Very Large Telescope data set. We find that the OMP population is slightly flattened with a low amount of rotation (∼0.8 km s-1) and with a velocity dispersion that follows a Plummer profile. The YMR population displays a high amount of rotation (∼5 km s-1) and a high degree of flattening, with a lower and flat velocity dispersion profile. The IMR population shows a high but flat velocity dispersion profile, with some degree of rotation (∼2 km s-1). We complement our MUSE data with information from Gaia DR2 and confirm that the stars from the OMP and YMR populations are comoving in 3D space, suggesting that they are dynamically bound. While dynamical evolutionary effects (e.g., energy equipartition) are able to explain the differences in velocity dispersion between the stellar populations, the strong differences in rotation indicate different formation paths for the populations, as supported by an N-body simulation tailored to emulate the YMR-OMP system. This study provides additional evidence for the M54 formation scenario proposed in our previous work, where this NSC formed via GC accretion (OMP) and in situ formation from gas accretion in a rotationally supported disk (YMR).

Keywords: Globular star clusters, Sagittarius dwarf spheroidal galaxy, Dwarf spheroidal galaxies, Galaxy nuclei
A New Likely Redback Millisecond Pulsar Binary with a Massive Neutron Star: 4FGL J2333.1-5527. We present the discovery of a likely new redback millisecond pulsar (MSP) binary associated with the Fermi γ-ray source 4FGL J2333.1-5527. Using optical photometric and spectroscopic observations from the Southern Astrophysical Research telescope, we identify a low-mass, main-sequence-like companion in a 6.9 hr, highly inclined orbit around a suspected massive neutron star primary. Archival XMM-Newton X-ray observations show this system has a hard power-law spectrum Γ = 1.6 ± 0.3 and LX ∼ 5 × 1031 erg s-1, consistent with redback MSP binaries. Our data suggest that for secondary masses typical of redbacks, the mass of the neutron star is likely well in excess of ∼1.4 M☉, but future timing of the radio pulsar is necessary to bolster this tentative conclusion. This work shows that a bevy of nearby compact binaries still await discovery, and that unusually massive neutron stars continue to be common in redbacks.

Keywords: Low-mass x-ray binary stars, Compact binary stars, Gamma-rays, Millisecond pulsars
Distribution of Water Vapor in Molecular Clouds. II. The depth-dependent abundance of both gas-phase and solid-state water within dense, quiescent, molecular clouds is important to both the cloud chemistry and gas cooling. Where water is in the gas phase, it is free to participate in the network of ion-neutral reactions that lead to a host of oxygen-bearing molecules, and its many ortho- and para-energy levels make it an effective coolant for gas temperatures greater than 20 K. Where water is abundant as ice on grain surfaces, and unavailable to cool the gas, significant amounts of oxygen are removed from the gas phase, suppressing the gas-phase chemical reactions that lead to a number of oxygen-bearing species, including O2. Models of far-UV (FUV)-illuminated clouds predict that the gas-phase water abundance peaks in the range AV ∼ 3 and 8 mag of the cloud surface, depending on the gas density and FUV field strength. Deeper within such clouds, water is predicted to exist mainly as ice on grain surfaces. More broadly, these models are used to analyze a variety of other regions, including outflow cavities associated with young stellar objects and the surface layers of protoplanetary disks. In this paper, we report the results of observational tests of FUV-illuminated cloud models toward the Orion Molecular Ridge and Cepheus B using data obtained from the Herschel Space Observatory and the Five College Radio Astronomy Observatory. Toward Orion, 2220 spatial positions were observed along the face-on Orion Ridge in the H2O 110- 101 557 GHz and NH3 J, K = 1,0-0,0 572 GHz lines. Toward Cepheus B, two strip scans were made in the same lines across the edge-on ionization front. These new observations demonstrate that gas-phase water exists primarily within a few magnitudes of dense cloud surfaces, strengthening the conclusions of an earlier study based on a much smaller data set, and indirectly supports the prediction that water ice is quite abundant in dense clouds.

Keywords: Interstellar molecules, Interstellar abundances, Astrochemistry
Paβ, Hα, and Attenuation in NGC 5194 and NGC 6946. We combine Hubble Space Telescope Paschen β (Paβ) imaging with ground-based, previously published Hα maps to estimate the attenuation affecting Hα, A(Hα), across the nearby, face-on galaxies NGC 5194 and NGC 6946. We estimate A(Hα) in ∼2000 independent 2″ ∼ 75 pc diameter apertures in each galaxy, spanning out to a galactocentric radius of almost 10 kpc. In both galaxies, A(Hα) drops with radius, with a bright, high-attenuation inner region, though in detail the profiles differ between the two galaxies. Regions with the highest attenuation-corrected Hα luminosity show the highest attenuation, but the observed Hα luminosity of a region is not a good predictor of attenuation in our data. Consistent with much previous work, the IR-to-Hα color does a good job of predicting A(Hα). We calculate the best-fit empirical coefficients for use combining Hα with 8, 12, 24, 70, or 100 μm to correct for attenuation. These agree well with previous work, but we also measure significant scatter around each of these linear relations. The local atomic plus molecular gas column density, N(H), also predicts A(Hα) well. We show that a screen with magnitude ∼0.2 times that expected for a Milky Way gas-to-dust value does a reasonable job of explaining A(Hα) as a function of N(H). This could be expected if only ∼40% of gas and dust directly overlap regions of Hα emission.

Keywords: Star formation, Interstellar dust extinction, Galaxies
Potential Vorticity Mixing in a Tangled Magnetic Field. A theory of potential vorticity (PV) mixing in a disordered (tangled) magnetic field is presented. The analysis is in the context of β-plane MHD, with a special focus on the physics of momentum transport in the stably stratified, quasi-2D solar tachocline. A physical picture of mean PV evolution by vorticity advection and tilting of magnetic fields is proposed. In the case of weak field perturbations, quasi-linear theory predicts that the Reynolds and magnetic stresses balance as turbulence Alfvénizes for a larger mean magnetic field. Jet formation is explored quantitatively in the mean field-resistivity parameter space. However, since even a modest mean magnetic field leads to large magnetic perturbations for large magnetic Reynolds number, the physically relevant case is that of a strong but disordered field. We show that numerical calculations indicate that the Reynolds stress is modified well before Alfvénization—I.e., before fluid and magnetic energies balance. To understand these trends, a double-average model of PV mixing in a stochastic magnetic field is developed. Calculations indicate that mean-square fields strongly modify Reynolds stress phase coherence and also induce a magnetic drag on zonal flows. The physics of transport reduction by tangled fields is elucidated and linked to the related quench of turbulent resistivity. We propose a physical picture of the system as a resisto-elastic medium threaded by a tangled magnetic network. Applications of the theory to momentum transport in the tachocline and other systems are discussed in detail.

Keywords: Magnetohydrodynamics, Solar differential rotation, Plasma astrophysics, Solar dynamo, Alfven waves, Solar magnetic fields, Astrophysical fluid dynamics