Sazuna/UAT_keywords huggingface dataset:
Magnetic Helicity Dissipation and Production in an Ideal MHD Code. We study a turbulent helical dynamo in a periodic domain by solving the ideal magnetohydrodynamic (MHD) equations with the FLASH code using the divergence-cleaning eight-wave method and compare our results with direct numerical simulations (DNS) using the Pencil Code. At low resolution, FLASH reproduces the DNS results qualitatively by developing the large-scale magnetic field expected from DNS, but at higher resolution, no large-scale magnetic field is obtained. In all those cases in which a large-scale magnetic field is generated, the ideal MHD results yield too little power at small scales. As a consequence, the small-scale current helicity is too small compared with that of the DNS. The resulting net current helicity has then always the wrong sign, and its statistical average also does not approach zero at late times, as expected from the DNS. Our results have implications for astrophysical dynamo simulations of stellar and galactic magnetism using ideal MHD codes.

Keywords: Interplanetary turbulence, Solar dynamo, Magnetohydrodynamical simulations
VVV Survey Microlensing: The Galactic Latitude Dependence. We search for microlensing events in fields along the Galactic minor axis, ranging from the Galactic center to -3°7 &lt; b &lt; 3°9 using the VISTA Variables in the Via Láctea (VVV) survey near-IR photometry. The new search is made across VVV tiles b291, b305, b319, b347, b361, and b375, covering a total area of about 11.5 deg2. We find a total of N = 238 new microlensing events in this new area, N = 74, which are classified as bulge red clump (RC) giant sources. Combining them with N = 122 events that we had previously reported in the Galactic center (VVV tile b333), allows us to study the latitude distribution of the microlensing events reaching the Galactic plane at b = 00 for the first time. We find a very strong dependence of the number of microlensing events with Galactic latitude, a number that increases rapidly toward the Galactic center by one order of magnitude from $| b| =2$ ° to b = 0° with a much steeper gradient than with Galactic longitude. The microlensing event population shows a flattened distribution (axial ratio b/a ≈ 1.5). The final sample shows a shorter mean timescale distribution than the Galactic plane sample for both the complete population and RC stars.

Keywords: Galactic center, Galaxy structure, Galactic bulge, Milky Way Galaxy physics, Gravitational lensing, Gravitational microlensing
Effects of 150-1000 eV Electron Impacts on Pure Carbon Monoxide Ices Using the Interstellar Energetic-Process System (IEPS). Pure CO ice has been irradiated with electrons of energy in the range 150-1000 eV with the Interstellar Energetic-Process System. The main products of irradiation are carbon chains Cn (n = 3, 5, 6, 8, 9, 10, 11, 12), suboxides, CnO (n = 2, 3, 4, 5, 6, 7), and CnO2 (n = 1, 3, 4, 5, 7) species. CO2 is by far the most abundant reaction product in all the experiments. The destruction cross section of CO peaks at about 250 eV, decreases with the energy of the electrons and is more than one order of magnitude higher than for gas-phase CO ionization. The production cross section of carbon dioxide has been also derived and is characterized by the competition between chemistry and desorption. Desorption of CO and of new species during the radiolysis follows the electron distribution in the ice. Low-energy electrons having short penetration depths induce significant desorption. Finally, as the ice thickness approaches the electron penetration depth the abundance of the products starts to saturate. Implications on the atmospheric photochemistry of cold planets hosting surface CO ices are also discussed.

Keywords: Laboratory astrophysics, Protoplanetary disks, Astrochemistry
GS 2000+25: The Least Luminous Black Hole X-Ray Binary. Little is known about the properties of the accretion flows and jets of the lowest-luminosity quiescent black holes. We report new, strictly simultaneous radio and X-ray observations of the nearby stellar-mass black hole X-ray binary GS 2000+25 in its quiescent state. In deep Chandra observations we detect the system at a faint X-ray luminosity of ${L}_{{\rm{X}}}={1.1}_{-0.7}^{+1.0}\times {10}^{30}{(d/2\mathrm{kpc})}^{2}$ erg s-1 (1-10 keV). This is the lowest X-ray luminosity yet observed for a quiescent black hole X-ray binary, corresponding to an Eddington ratio LX/LEdd ∼ 10-9. In 15 hours of observations with the Karl G. Jansky Very Large Array, no radio continuum emission is detected to a 3σ limit of &lt;2.8 μJy at 6 GHz. Including GS 2000+25, four quiescent stellar-mass black holes with LX &lt; 1032 erg s-1 have deep simultaneous radio and X-ray observations and known distances. These sources all have radio to X-ray luminosity ratios generally consistent with, but slightly lower than, the low-state radio/X-ray correlation for stellar-mass black holes with LX &gt; 1032 erg s-1. Observations of these sources tax the limits of our current X-ray and radio facilities, and new routes to black hole discovery are needed to study the lowest-luminosity black holes.

Keywords: Low-mass x-ray binary stars, Astrophysical black holes
Resolving the FU Orionis System with ALMA: Interacting Twin Disks?. FU Orionis objects are low-mass pre-main sequence stars characterized by dramatic outbursts several magnitudes in brightness. These outbursts are linked to episodic accretion events in which stars gain a significant portion of their mass. The physical processes behind these accretion events are not yet well understood. The archetypal FU Ori system, FU Orionis, is composed of two young stars with detected gas and dust emission. The continuum emitting regions have not been resolved until now. Here, we present 1.3 mm observations of the FU Ori binary system using the Atacama Large Millimeter/submillimeter Array. The disks are resolved at 40 mas resolution. Radiative transfer modeling shows that the emission from FU Ori north (primary) is consistent with a dust disk with a characteristic radius of ∼11 au. The ratio between the major and minor axes shows that the inclination of the disk is ∼37°. FU Ori south is consistent with a dust disk of similar inclination and size. Assuming the binary orbit shares the same inclination angle as the disks, the deprojected distance between the north and south components is 0"6, I.e., ∼250 au. Maps of 12CO emission show a complex kinematic environment with signature disk rotation at the location of the northern component, and also (to a lesser extent) for FU Ori south. The revised disk geometry allows us to update FU Ori accretion models, yielding a stellar mass and mass accretion rate of FU Ori north of 0.6 M⊙ and 3.8 × 10-5 M⊙ yr-1, respectively.

Keywords: FU Orionis stars, Millimeter astronomy, Star formation, Stellar accretion disks, Submillimeter astronomy, Circumstellar gas
Cosmological Simulation of Galaxy Groups and Clusters. I. Global Effect of Feedback from Active Galactic Nuclei. In this study we quantify the properties of the gas and dark matter around active galactic nuclei (AGNs) in simulated galaxy groups and clusters and analyze the effect of AGN feedback on the surrounding intracluster (group) medium. Our results suggest downsizing of AGN luminosity with host halo mass, supporting the results obtained from clustering studies of AGNs. By examining the temperature and density distribution of the gas in the vicinity of AGNs we show that due to feedback from the central engine, the gas gets displaced from the center of the group/cluster resulting in a reduction of the density but an enhancement of temperature. We show that these effects are pronounced at both high and low redshifts and propose new observables to study the effect of feedback in higher-redshift galaxies. We also show that the average stellar mass is decreased in halos in the presence of AGN feedback confirming claims from previous studies. Our work for the first time uses a fully cosmological hydrodynamic simulation to evaluate the global effects of AGN feedback on their host dark matter halos as well as galaxies at scales of galaxy groups and clusters.

Keywords: Galaxy clusters, Active galactic nuclei
S62 on a 9.9 yr Orbit around SgrA*. We present the Keplerian orbit of S62 around the supermassive black hole Sagittarius A* (SgrA*) in the center of our Galaxy. We monitor this S-star cluster member over more than a full orbit around SgrA* using the Very Large Telescope with the near-infrared instruments Spectrograph for INtegral Field Observations in the Near Infrared (SINFONI) and NAOS+CONICA (NACO). For that, we are deriving positional information from deconvolved images. We apply the Lucy-Richardson algorithm to the data sets. The NACO observations cover data from 2002 to 2018, and the SINFONI data cover 2008-2012. S62 can be traced reliably in both data sets. Additionally, we adapt one KECK data point for 2019 that supports the reidentification of S62 after the pericenter passage of S2. With ${t}_{\mathrm{period}}=9.9\,\mathrm{yr}$ and a periapse velocity of approximately 10% of the speed of light, S62 has the shortest known stable orbit around the supermassive black hole in the center of our Galaxy to date. From the analysis, we also derive the enclosed mass from a maximum likelihood method to be 4.15 ± 0.6 × 106M☉.

Keywords: S stars, Galactic center, Black holes
Evolution of the Deterministic Collapse Barrier of the Field Clusters as a Probe of Cosmology. The collapse barrier, δc, of the field clusters located in the low-density environment is deterministic rather than diffusive, unlike that of the wall counterparts located in the superclusters. Analyzing the data from the Mira-Titan simulations for 11 different cosmologies, including the standard ΛCDM cosmology at various redshifts, we investigate the evolution of the deterministic collapse barrier of the field clusters and explore its dependence on the background cosmology. Regardless of the background cosmology, the deterministic δc exhibits a universal behavior of having a higher value than the Einstein-de Sitter spherical collapse barrier height of δsc = 1.686, at z = 0, but gradually converging down to δsc as the dominance of dark energy diminishes with the increment of z. A significant difference among different cosmologies, however, is found in its convergence rate, as well as in the critical redshift zc, at which δc = δsc. Showing that the convergence rate and critical redshifts can distinguish even between the degenerate cosmologies, which yield almost identical linear growth factor and cluster mass functions, we suggest that the evolution of the deterministic collapse barrier of the field clusters should be a powerful complementary probe of cosmology.

Keywords: Cosmological models, Large-scale structure of the universe
Metallicity and α-Element Abundance Gradients along the Sagittarius Stream as Seen by APOGEE. Using 3D positions and kinematics of stars relative to the Sagittarius (Sgr) orbital plane and angular momentum, we identify 166 Sgr stream members observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE) that also have Gaia DR2 astrometry. This sample of 63/103 stars in the Sgr trailing/leading arm is combined with an APOGEE sample of 710 members of the Sgr dwarf spheroidal core (385 of them newly presented here) to establish differences of 0.6 dex in median metallicity and 0.1 dex in [α/Fe] between our Sgr core and dynamically older stream samples. Mild chemical gradients are found internally along each arm, but these steepen when anchored by core stars. With a model of Sgr tidal disruption providing estimated dynamical ages (I.e., stripping times) for each stream star, we find a mean metallicity gradient of 0.12 ± 0.03 dex Gyr-1 for stars stripped from Sgr over time. For the first time, an [α/Fe] gradient is also measured within the stream, at 0.02 ± 0.01 dex Gyr-1 using magnesium abundances and at 0.04 ± 0.01 dex Gyr-1 using silicon, which imply that the Sgr progenitor had significant radial abundance gradients. We discuss the magnitude of those inferred gradients and their implication for the nature of the Sgr progenitor within the context of the current family of Milky Way satellite galaxies, and we suggest that more sophisticated Sgr models are needed to properly interpret the growing chemodynamical detail we have on the Sgr system.

Keywords: Galaxy chemical evolution, Stellar kinematics, Stellar abundances, Dwarf galaxies, Chemical abundances, Tidal tails, Milky Way stellar halo, Galaxy abundances, Galaxy evolution, Sagittarius dwarf spheroidal galaxy
Continuum Enhancements, Line Profiles, and Magnetic Field Evolution during Consecutive Flares. During solar flares, magnetic energy can be converted into electromagnetic radiation from radio waves to γ-rays. Enhancements in the continuum at visible wavelengths, as well as continuum enhancements in the FUV and NUV passbands, give rise to white-light flares. In addition, the strong energy release in these events can lead to the rearrangement of the magnetic field at the photospheric level, causing morphological changes in large and stable magnetic structures like sunspots. In this context, we describe observations acquired by satellite instruments (Interface Region Imaging Spectrograph (IRIS), Solar Dynamics Observatory/Helioseismic and Magnetic Imager, Hinode/Solar Optical Telescope) and ground-based telescopes (Rapid Oscillations in the Solar Atmosphere (ROSA)/Dunn Solar Telescope) during two consecutive C7.0 and X1.6 flares that occurred in active region NOAA 12205 on 2014 November 7. The flare was accompanied by an eruption. The results of the analysis show the presence of continuum enhancements during the evolution of the events, observed both in ROSA images and in IRIS spectra. In the latter, a prominent blueshifted component is observed at the onset of the eruption. We investigate the role played by the evolution of the δ sunspots of the active region in the flare triggering, and finally we discuss the changes in the penumbrae surrounding these sunspots as a further consequence of these flares.

Keywords: High resolution spectroscopy, Solar flares, Solar magnetic reconnection, Solar photosphere, Solar ultraviolet emission, Solar white-light flares, Solar magnetic fields, Solar transition region, Solar chromosphere, Active solar chromosphere
HST/STIS Capability for Love Number Measurement of WASP-121b. Data from transit light curves, radial velocity, and transit timing observations can be used to probe the interiors of exoplanets beyond the mean density, by measuring the Love numbers h2 and k2. The first indirect estimate of k2 for an exoplanet from radial velocity and transit timing variation observations has been performed by taking advantage of the years-spanning baseline. Not a single measurement of h2 has been achieved from transit light curves, mostly because the photometric precision of current observing facilities is still too low. We show that the Imaging Spectrograph instrument onboard the Hubble Space Telescope (HST) could measure h2 of the hot Jupiter WASP-121b if only a few more observations were gathered. We show that a careful treatment of the noise and stellar limb darkening (LD) must be carried out to achieve a measurement of h2. In particular, we find that the impact of the noise modeling on the estimation of h2 is stronger than that of the LD modeling. In addition, we emphasize that the wavelet method for correlated noise analysis can mask limb brightening. Finally, using currently available data, we briefly discuss the tentative measurement of ${h}_{2}={1.39}_{-0.81}^{+0.71}$ in terms of interior structure. Additional observations would further constrain the interior of WASP-121b and possibly provide insights on the physics of inflation. The possibility of using the approach presented here with the HST provides a bridge before the high-quality data to be returned by the James Webb Space Telescope and PLATO telescope in the coming decade.

Keywords: Hot Jupiters, Planetary interior, HST photometry
Condensation of Atomic Carbon: Possible Routes toward Glycine. Many organic molecules including amino acids and nucleobases are expected to be formed in astrophysical environments. In this article, we used both experimental and computational approaches to test the possibility of the glycine formation in the interstellar medium via C atom addition to ice mantels of dust particles. The reactions of C atoms with NH3 and H2 were studied experimentally. These reactions are found to be highly exothermic and barrierless, leading to the formation of the products CH2NH and HCH. These product molecules are formed in excited states and therefore could immediately take part even in chemical reactions with energy barriers. The CH2NH molecule is formed in the long-lived triplet state, which is above the most energetically favorable singlet state of about 20,918 cm-1 (∼250 kJ mol-1). Therefore, based on the results of quantum chemical computations the following two pathways can take place at low temperature. The first one is C + H2 → HCH followed by NH3 + HCH + CO2 → glycine. The second one is C + NH3 → CH2NH followed by CH2NH + CO + H2O → glycine or CH2NH + CO2 + H2 → glycine. The first pathway was also tested experimentally by adding C atoms to ice clusters containing H2, NH3, and CO2 molecules. The detection of the main mass peak of glycine supported the feasibility of the proposed pathway.

Keywords: Astrochemistry, Astrophysical dust processes, Astrobiology, Dark interstellar clouds, Interstellar dust processes, Pre-biotic astrochemistry
Xenon Isotopes Identify Large-scale Nucleosynthetic Heterogeneities across the Solar System. Nucleosynthetic isotopic anomalies in meteorites and planetary objects contribute to our understanding of the formation of the solar system. Isotope systematics of chondrites demonstrate the existence of a physical separation between isotopic reservoirs in the solar system. The isotopic composition of atmospheric xenon (Xe) indicates that its progenitor, U-Xe, is depleted in 134Xe and 136Xe isotopes relative to solar or chondritic end-members. This deficit supports the view that nucleosynthetic heterogeneities persisted during the solar system formation. Measurements of xenon emitted from comet 67P/Churyumov-Gerasimenko (67P) identified a similar, but more extreme, deficit of cometary gas in these isotopes relative to solar gas. Here we show that the data from 67P demonstrate that two distinct sources contributed xenon isotopes associated with the r-process to the solar system. The h-process contributed at least 29% (2σ) of solar system 136Xe. Mixtures of these r-process components and the s-process that match the heavy isotope signature of cometary Xe lead to depletions of the precursor of atmospheric Xe in p-only isotopes. Only the addition of pure p-process Xe to the isotopic mixture brings 124Xe/132Xe and 126Xe/132Xe ratios back to solar-like values. No pure p-process Xe has been detected in solar system material, and variation in p-process Xe isotopes is always correlated with variation in r-process Xe isotopes. In the solar system, p-process incorporation from the interstellar medium happened before incorporation of r-process nuclides or material in the outer edge of the solar system carries a different mixture of presolar sources as have been preserved in parent bodies.

Keywords: Cosmochemistry, Nucleosynthesis, Solar system planets, Earth atmosphere, Planetary atmospheres, P-process
Filling the Magnetospheres of Weak Pulsars. Recent advances in numerical algorithms and computational power have enabled first-principles simulations of pulsar magnetospheres using particle-in-cell techniques. These ab initio simulations seem to indicate that pair creation through photon-photon collision at the light cylinder is required to sustain the pulsar engine. However, for many rotation-powered pulsars, pair creation operates effectively only near the stellar surface where magnetic field is high. How these "weak pulsars" fill their magnetospheres without efficient photon-photon pair conversion in the outer magnetosphere is still an open question. In this paper, we present a range of self-consistent solutions to the pulsar magnetosphere that do not require pair production near the light cylinder. When pair production is very efficient near the star, the pulsar magnetosphere converges to previously reported solutions. However, in the intermediate regime, where pair supply is barely enough to sustain the magnetospheric current, we observe a time-dependent solution with a quasi-period about half of the rotation period. This new quasi-periodic solution may explain the observed pulsar death line without invoking multipolar components near the star, and can potentially explain the core versus conal emission patterns observed in pulsar radio signals.

Keywords: Neutron stars, Magnetic fields, Plasma astrophysics, Rotation powered pulsars
Variations in the Width, Density, and Direction of the Palomar 5 Tidal Tails. Stars that escape globular clusters form tidal tails that are predominantly shaped by the global distribution of mass in the Galaxy, but also preserve a historical record of small-scale perturbations. Using deep grz photometry from DECaLS, we present highly probable members of the tidal tails associated with the evaporating globular cluster Palomar 5. These data yield the cleanest view of a stellar stream beyond ≈20 kpc and reveal: (1) a wide, low surface-brightness extension of the leading tail; (2) significant density variations along the stream; and (3) sharp changes in the direction of both the leading and the trailing tail. In the fiducial Milky Way model, a rotating bar perturbs the Palomar 5 tails and can produce streams with similar width and density profiles to those observed. However, the deviations of the stream track in this simple model do not match those observed in the Palomar 5 trailing tail, indicating the need for an additional source of perturbation. These discoveries open up the possibility of measuring the population of perturbers in the Milky Way, including dark-matter subhalos, with an ensemble of stellar streams and deep photometry alone.

Keywords: Globular star clusters, Milky Way dark matter halo, Milky Way dynamics, Tidal tails, Milky Way stellar halo
Spectral Evolution of the Ultraluminous X-Ray Sources M82 X-1 and X-2. M82 hosts two well-known ultraluminous X-ray sources (ULXs). X-1, an intermediate-mass black hole (IMBH) candidate, and X-2, an ultraluminous X-ray pulsar. Here, we present a broadband X-ray spectral analysis of both sources based on 10 simultaneous observations made with Chandra and NuSTAR. Chandra provides the high spatial resolution to resolve the crowded field in the 0.5-8 keV band, and NuSTAR provides the sensitive hard X-ray spectral data, extending the bandpass of our study above 10 keV. These observations, taken in 2015-2016, cover a period of flaring from X-1, allowing us to study the spectral evolution of this source with luminosity. During four of these observations, X-2 was found to be at a low flux level, allowing an unambiguous view of the emission from X-1. We find that the broadband X-ray emission from X-1 is consistent with that seen in other ULXs observed in detail with NuSTAR, with a spectrum that includes a broadened disk-like component and a high-energy tail. We find that the luminosity of the disk scales with inner disk temperature as L ∝ T-3/2, contrary to expectations of a standard accretion disk and previous results. These findings rule out a thermal state for sub-Eddington accretion, and therefore do not support M82 X-1 as an IMBH candidate. We also find evidence that the neutral column density of the material in the line of sight increases with ${L}_{{\rm{X}}}$ , perhaps due to an increased mass outflow with accretion rate. For X-2, we do not find any significant spectral evolution, but we find the spectral parameters of the phase-averaged broadband emission are consistent with the pulsed emission at the highest X-ray luminosities.

Keywords: Neutron stars, Intermediate-mass black holes, X-ray point sources, Stellar mass black holes, Pulsars, X-ray sources, Astrophysical black holes