Sazuna/UAT_keywords huggingface dataset:
The Origin of the E/Z Isomer Ratio of Imines in the Interstellar Medium. Recent astronomical observations of both isomers E and Z of imines such as cyanomethanimine, ethanimine, and 2-propyn-1-imine have revealed that the abundances in the interstellar medium (ISM) of these isomers differ by factors of ∼3-10. Several theories have been proposed to explain the observed behavior, but none of them successfully explains the [E]/[Z] ratios. In this work we present a detailed study of the kinetics of the one-step E-Z isomerization reactions of cyanomethanimine, ethanimine, and 2-propyn-1-imine under interstellar conditions (in the 10-400 K temperature range). This reaction was previously thought to be nonviable in the ISM due to its associated high-energy barrier (about 13,000 K). In this Letter, we show that considering the multidimensional small curvature tunneling approximation, the tunneling effect enables the isomerization even at low temperatures. This is due to the fact that the representative tunneling energy lies in the vibrational ground state of the least stable isomer up to approximately 150 K, making the reaction constants of the isomerization from the least stable to the most stable isomer basically constant. The predicted [E]/[Z] ratios are almost the same as those reported from the astronomical observations for all imines observed. This study demonstrates that the [E]/[Z] ratio of imines in the ISM strongly depends on their relative stability.

Keywords: Interstellar clouds, Reaction rates, Pre-biotic astrochemistry, Astrochemistry
A Low-mass Cold and Quiescent Core Population in a Massive Star Protocluster. Pre-stellar cores represent the initial conditions of star formation. Although these initial conditions in nearby low-mass star-forming regions have been investigated in detail, such initial conditions remain vastly unexplored for massive star-forming regions. We report the detection of a cluster of low-mass starless and pre-stellar core candidates in a massive star protocluster-forming cloud, NGC 6334S. With the Atacama Large Millimeter/submillimeter Array (ALMA) observations at a ∼0.02 pc spatial resolution, we identified 17 low-mass starless core candidates that do not show any evidence of protostellar activity. These candidates present small velocity dispersions, high fractional abundances of NH2D, high NH3 deuterium fractionations, and are completely dark in the infrared wavelengths from 3.6 up to 70 μm. Turbulence is significantly dissipated and the gas kinematics are dominated by thermal motions toward these candidates. Nine out of the 17 cores are gravitationally bound, and therefore are identified as pre-stellar core candidates. The embedded cores of NGC 6334S show a wide diversity in masses and evolutionary stages.

Keywords: Early-type stars, Interstellar line emission, Infrared dark clouds, Star forming regions, Protoclusters, Star formation, Interstellar medium
A Real-time View of Orbital Evolution in HM Cancri. HM Cancri is a double degenerate binary with the shortest orbital period presently known. The 5.36 minute period is seen as a large amplitude, soft X-ray modulation, likely resulting from a hot spot produced by direct impact accretion. With such a short orbital period it is expected to have a gravitational wave luminosity comparable to or larger than that in the X-ray, and its orbital frequency is known to be increasing at a rate consistent with the expected loss of angular momentum due to gravitational radiation. We use recent Neutron Star Interior Composition Explorer observations to extend its long-term X-ray timing baseline to almost 20 yr. Phase coherent timing of these new data combined with existing Chandra data demonstrates conclusively that the rate of orbital frequency increase is slowing, and we measure a nonzero ${\ddot{f}}_{0}=-8.95\pm 1.4\times {10}^{-27}$ Hz s-2, which is to our knowledge the first such measurement of its kind for any compact astrophysical binary. With the simultaneous high precision measurement of ${\dot{f}}_{0}=3.557\pm 0.005\times {10}^{-16}$ Hz s-1, we estimate that the system will reach its maximum orbital frequency of ${f}_{\max }\approx 3.1172091$ mHz in 1260 ± 200 yr, indicating that the system is close to its epoch of maximum orbital frequency. Assuming mass transfer is conservative, the measurement of $\ddot{f}\lt 0$ implies that the accretion rate from the donor is growing, with $-5.4\times {10}^{-10}\lt {\ddot{M}}_{2}\lt -4.0\times {10}^{-10}$ M⊙ yr-2. Further quantitative comparisons with theoretical models should enable more precise inferences regarding its current evolutionary state.

Keywords: Accretion, X-ray binary stars, White dwarf stars, AM Canum Venaticorum stars, Compact binary stars, Interacting binary stars, Orbital evolution, X-ray sources
uGMRT Observations of a Fast and Blue Optical Transient—AT 2018cow. We present low-fRequency radio observations of a fast-rising blue optical transient (FBOT), AT 2018cow, with the upgraded Giant Metrewave Radio Telescope (uGMRT). Our observations span t = 11-570 days post-explosion and a frequency range of 250-1450 MHz. The uGMRT light curves are best modeled as synchrotron emission from an inhomogeneous radio-emitting region expanding into an ionized medium. However, due to the lack of information on the source covering factor, which is a measure of the degree of inhomogeneity, we derive various parameters assuming the source covering factor to be unity. These parameters, hence, indicate limits on the actual values in an inhomogeneous model. We derive the lower limit of the shock radius to be R ∼ (6.1-14.4) × 1016 cm at t = 138-257 days post-explosion. We find that the fast-moving ejecta from the explosion are moving with velocity v &gt; 0.2c up to t = 257 days post-explosion. The upper limits of the mass-loss rate of the progenitor are $\dot{M}$ ∼ (4.1-1.7) × 10-6 M⊙ yr-1 at (19.3-45.7) years before the explosion for a wind velocity vw = 1000 km s-1. These $\dot{M}$ values are ∼ 100 times smaller than the previously reported mass-loss rate 2.2 years before the explosion, indicating an enhanced phase of the mass-loss event close to the end-of-life of the progenitor. Our results are in line with the speculation of the presence of a dense circumstellar shell in the vicinity of AT 2018cow from previous radio, ultra-violet, and optical observations.

Keywords: Circumstellar matter, Non-thermal radiation sources, Radio transient sources
Mapping the Universe Expansion: Enabling Percent-level Measurements of the Hubble Constant with a Single Binary Neutron-star Merger Detection. The joint observation of the gravitational-wave (GW) and electromagnetic (EM) signal from the binary neutron-star merger GW170817 allowed for a new independent measurement of the Hubble constant H0, albeit with an uncertainty of about 15% at 1σ. Observations of similar sources with a network of future detectors will allow for more precise measurements of H0. These, however, are currently largely limited by the intrinsic degeneracy between the luminosity distance and the inclination of the source in the GW signal. We show that the higher-order modes in gravitational waves can be used to break this degeneracy in astrophysical parameter estimation in both the inspiral and post-merger phases of a neutron star merger. We show that for systems at distances similar to GW170817, this method enables percent-level measurements of H0 with a single detection. This would permit the study of time variations and spatial anisotropies of H0 with unprecedented precision. We investigate how different network configurations affect measurements of H0, and discuss the implications in terms of science drivers for the proposed 2.5- and third-generation GW detectors. Finally, we show that the precision of H0 measured with these future observatories will be solely limited by redshift measurements of EM counterparts.

Keywords: Gravitational waves
Thiols in the Interstellar Medium: First Detection of HC(O)SH and Confirmation of C<SUB>2</SUB>H<SUB>5</SUB>SH. The chemical compounds carrying the thiol group (-SH) have been considered essential in recent prebiotic studies regarding the polymerization of amino acids. We have searched for this kind of compound toward the Galactic Center quiescent cloud G+0.693-0.027. We report the first detection in the interstellar space of the trans-isomer of monothioformic acid (t-HC(O)SH) with an abundance of ∼1 × 10-10. Additionally, we provide a solid confirmation of the gauche isomer of ethyl mercaptan (g-C2H5SH) with an abundance of ∼3 × 10-10, and we also detect methyl mercaptan (CH3SH) with an abundance of ∼5 × 10-9. Abundance ratios were calculated for the three SH-bearing species and their OH analogs, revealing similar trends between alcohols and thiols with increasing complexity. Possible chemical routes for the interstellar synthesis of t-HC(O)SH, CH3SH, and C2H5SH are discussed, as well as the relevance of these compounds in the synthesis of prebiotic proteins in the primitive Earth.

Keywords: Interstellar molecules, Galactic center, Chemical abundances, Astrochemistry
Observations of the Quiet Sun during the Deepest Solar Minimum of the Past Century with Chandrayaan-2 XSM: Elemental Abundances in the Quiescent Corona. Elements with low first ionization potential (FIP) are known to be 3-4 times more abundant in active region loops of the solar corona than in the photosphere. There have been observations suggesting that this observed "FIP bias" may be different in other parts of the solar corona and such observations are thus important in understanding the underlying mechanism. The Solar X-ray Monitor (XSM) on board the Chandrayaan-2 mission carried out spectroscopic observations of the Sun in soft X-rays during the 2019-2020 solar minimum, considered to be the quietest solar minimum of the past century. These observations provided a unique opportunity to study soft X-ray spectra of the quiescent solar corona in the absence of any active regions. By modeling high-resolution broadband X-ray spectra from XSM, we estimate the temperature and emission measure during periods of possibly the lowest solar X-ray intensity. We find that the derived parameters remain nearly constant over time with a temperature around 2 MK, suggesting the emission is dominated by X-ray bright points. We also obtain the abundances of Mg, Al, and Si relative to H, and find that the FIP bias is ∼2, lower than the values observed in active regions.

Keywords: Solar abundances, Quiet sun
Observations of the Quiet Sun during the Deepest Solar Minimum of the Past Century with Chandrayaan-2 XSM: Sub-A-class Microflares outside Active Regions. Solar flares, with energies ranging over several orders of magnitude, result from impulsive release of energy due to magnetic reconnection in the corona. Barring a handful, almost all microflares observed in X-rays are associated with the solar active regions. Here we present, for the first time, a comprehensive analysis of a large sample of quiet-Sun microflares observed in soft X-rays by the Solar X-ray Monitor (XSM) on board the Chandrayaan-2 mission during the 2019-2020 solar minimum. A total of 98 microflares having peak flux below GOES A-level were observed by the XSM during observations spanning 76 days. By using the derived plasma temperature and emission measure of these events obtained by fitting the XSM spectra along with volume estimates from concurrent imaging observations in EUV with the Solar Dynamics Observatory/Atmospheric Imaging Assembly, we estimated their thermal energies to be ranging from 3 × 1026 to 6 × 1027 erg. We present the frequency distribution of the quiet-Sun microflares with energy and discuss the implications of these observations of small-scale magnetic reconnection events outside active regions on coronal heating.

Keywords: Quiet sun, Solar x-ray flares
How Likely Are Snowball Episodes Near the Inner Edge of the Habitable Zone?. Understanding when global glaciations occur on Earth-like planets is a major challenge in climate evolution research. Most models of how greenhouse gases like CO2 evolve with time on terrestrial planets are deterministic, but the complex, nonlinear nature of Earth's climate history motivates study of nondeterministic climate models. Here a maximally simple stochastic model of CO2 evolution and climate on an Earth-like planet with an imperfect CO2 thermostat is investigated. It is shown that as stellar luminosity is increased in this model, the decrease in the average atmospheric CO2 concentration renders the climate increasingly unstable, with excursions to a low-temperature state common once the received stellar flux approaches that of present-day Earth. Unless climate feedbacks always force the variance in CO2 concentration to decline rapidly with received stellar flux, this means that terrestrial planets near the inner edge of the habitable zone may enter Snowball states quite frequently. Observations of the albedos and color variation of terrestrial-type exoplanets should allow this prediction to be tested directly in the future.

Keywords: Exoplanets, Earth (planet), Surface ices, Habitable zone, Habitable planets, Greenhouse gases
Sympathetic Standard and Blowout Coronal Jets Observed in a Polar Coronal Hole. We present the sympathetic eruption of a standard and a blowout coronal jet originating from two adjacent coronal bright points (CBP1 and CBP2) in a polar coronal hole, using soft X-ray and extreme-ultraviolet observations respectively taken by the Hinode and the Solar Dynamics Observatory. In the event, a collimated jet with obvious westward lateral motion first launched from CBP1, during which a small bright point appeared around CBP1's east end, and magnetic flux cancellation was observed within the eruption source region. Based on these characteristics, we interpret the observed jet as a standard jet associated with photospheric magnetic flux cancellation. About 15 minutes later, the westward-moving jet spire interacted with CBP2 and resulted in magnetic reconnection between them, which caused the formation of the second jet above CBP2 and the appearance of a bright loop system in between the two CBPs. In addition, we observed the writhing, kinking, and violent eruption of a small kink structure close to CBP2's west end but inside the jet base, which made the second jet brighter and broader than the first one. These features suggest that the second jet should be a blowout jet triggered by the magnetic reconnection between CBP2 and the spire of the first jet. We conclude that the two successive jets were physically connected to each other rather than a temporal coincidence, and this observation also suggests that coronal jets can be triggered by external eruptions or disturbances, as well as internal magnetic activities or magnetohydrodynamic instabilities.

Keywords: Solar corona, Solar flares, Solar x-ray emission
Primordial Giant Planet Obliquity Driven by a Circumplanetary Disk. Detached circumplanetary disks are unstable to tilting as a result of the stellar tidal potential. We examine how a tilted circumplanetary disk affects the evolution of the spin axis of an oblate planet. The disk is evolved using time-dependent equations for linear wave-like warp evolution, including terms representing the effect of the tidal potential and planetary oblateness. For a disk with a sufficiently large mass, we find that the planet spin quickly aligns to the misaligned disk. The tilt of the planetary spin axis then increases on the same timescale as the disk. This can be an efficient mechanism for generating primordial obliquity in giant planets. We suggest that directly imaged exoplanets at large orbital radii, where the disk mass criterion is more likely to be satisfied, could have significant obliquities due to the tilt instability of their circumplanetary disks.

Keywords: Planetary theory, Planetary-disk interactions, Hydrodynamics, Planetary alignment, Solar system gas giant planets, Exoplanet evolution, Pre-main sequence stars, Protoplanetary disks, Star-planet interactions, Exoplanet formation, Extrasolar gaseous giant planets, Planet formation
The Extraordinary Outburst in the Massive Protostellar System NGC 6334 I-MM1: Strong Increase in Mid-Infrared Continuum Emission. In recent years, dramatic outbursts have been identified toward massive protostars via infrared and millimeter dust continuum and molecular maser emission. The longest lived outburst (&gt;6 yr) persists in NGC 6334 I-MM1, a deeply embedded object with no near-IR counterpart. Using FORCAST and HAWC+ on SOFIA, we have obtained the first mid-IR images of this field since the outburst began. Despite being undetected in pre-outburst ground-based 18 μm images, MM1 is now the brightest region at all three wavelengths (25, 37, and 53 μm), exceeding the UCHII region MM3 (NGC 6334 F). Combining the SOFIA data with ALMA imaging at four wavelengths, we construct a spectral energy distribution of the combination of MM1 and the nearby hot core MM2. The best-fit Robitaille radiative transfer model yields a luminosity of (4.9 ± 0.8) × 104 L☉. Accounting for an estimated pre-outburst luminosity ratio MM1:MM2 = 2.1 ± 0.4, the luminosity of MM1 has increased by a factor of 16.3 ± 4.4. The pre-outburst luminosity implies a protostar of mass 6.7 M☉, which can produce the ionizing photon rate required to power the pre-outburst HCHII region surrounding the likely outbursting protostar MM1B. The total energy and duration of the outburst exceed the S255IR-NIRS3 outburst by a factor of ≳3, suggesting a different scale of event involving expansion of the protostellar photosphere (to ≳20 R☉), thereby supporting a higher accretion rate (≳0.0023 M☉ yr-1) and reducing the ionizing photon rate. In the grid of hydrodynamic models of Meyer et al., the combination of outburst luminosity and magnitude (3) places the NGC 6334 I-MM1 event in the region of moderate total accretion (∼0.1-0.3 M☉) and hence long duration (∼40-130 yr).

Keywords: Accretion, Millimeter astronomy, Stellar jets, Protostars, Far infrared astronomy, Infrared astronomy, Star formation, Dust continuum emission, Interstellar masers, Radio continuum emission, Submillimeter astronomy, Radio interferometry
Multimessenger Signals from Black Hole-Neutron Star Mergers without Significant Tidal Disruption. We study the multimessenger signals from the merger of a black hole with a magnetized neutron star using resistive magnetohydrodynamics simulations coupled to full general relativity. We focus on a case with a 5:1 mass ratio, where only a small amount of the neutron star matter remains post-merger, but we nevertheless find that significant electromagnetic radiation can be powered by the interaction of the neutron star's magnetosphere with the black hole. In the lead-up to merger, strong twisting of magnetic field lines from the inspiral leads to plasmoid emission and results in a luminosity in excess of that expected from unipolar induction. We find that the strongest emission occurs shortly after merger during a transitory period in which magnetic loops form and escape the central region. The remaining magnetic field collimates around the spin axis of the remnant black hole before dissipating, an indication that, in more favorable scenarios (higher black hole spin/lower mass ratio) with larger accretion disks, a jet would form.

Keywords: Neutron stars, Gravitational waves, Einstein field equations, Astrophysical black holes, Magnetohydrodynamical simulations
The Single-cloud Star Formation Relation. One of the most important and well-established empirical results in astronomy is the Kennicutt-Schmidt relation between the density of interstellar gas and the rate at which that gas forms stars. A tight correlation between these quantities has long been measured at galactic scales. More recently, using surveys of YSOs, a KS relationship has been found within molecular clouds relating the surface density of star formation to the surface density of gas; however, the scaling of these laws varies significantly from cloud to cloud. In this Letter, we use a recently developed, high-accuracy catalog of young stellar objects from Spitzer combined with high-dynamic-range gas column density maps of 12 nearby (&lt;1.5 kpc) molecular clouds from Herschel to re-examine the KS relation within individual molecular clouds. We find a tight, linear correlation between clouds' star formation rate per unit area and their gas surface density normalized by the gas freefall time. The measured intracloud KS relation, which relates star formation rate to the volume density, extends over more than two orders of magnitude within each cloud and is nearly identical in each of the 12 clouds, implying a constant star formation efficiency per freefall time ϵff ≈ 0.026. The finding of a universal correlation within individual molecular clouds, including clouds that contain no massive stars or massive stellar feedback, favors models in which star formation is regulated by local processes such as turbulence or stellar feedback such as protostellar outflows, and disfavors models in which star formation is regulated only by galaxy properties or supernova feedback on galactic scales.

Keywords: Early stellar evolution, Star forming regions, Molecular clouds, Scaling relations, Far infrared astronomy, Infrared astronomy, Young stellar objects, Star formation, Dust continuum emission, Protostars
Resolving the Complex Evolution of a Supermassive Black Hole Triplet in a Cosmological Simulation. We present here a self-consistent cosmological zoom-in simulation of a triple supermassive black hole (SMBH) system forming in a complex multiple galaxy merger. The simulation is run with an updated version of our code KETJU, which is able to follow the motion of SMBHs down to separations of tens of Schwarzschild radii while simultaneously modeling the large-scale astrophysical processes in the surrounding galaxies, such as gas cooling, star formation, and stellar and AGN feedback. Our simulation produces initially an SMBH binary system for which the hardening process is interrupted by the late arrival of a third SMBH. The KETJU code is able to accurately model the complex behavior occurring in such a triple SMBH system, including the ejection of one SMBH to a kiloparsec-scale orbit in the galaxy due to strong three-body interactions as well as Lidov-Kozai oscillations suppressed by relativistic precession when the SMBHs are in a hierarchical configuration. One pair of SMBHs merges ∼3 Gyr after the initial galaxy merger, while the remaining binary is at a parsec-scale separation when the simulation ends at redshift z = 0. We also show that KETJU can capture the effects of the SMBH binaries and triplets on the surrounding stellar population, which can affect the binary merger timescales as the stellar density in the system evolves. Our results demonstrate the importance of dynamically resolving the complex behavior of multiple SMBHs in galactic mergers, as such systems cannot be readily modeled using simple orbit-averaged semianalytic models.

Keywords: Supermassive black holes, Galaxy mergers, Astronomical simulations
Evolution of Solar Wind Turbulence from 0.1 to 1 au during the First Parker Solar Probe-Solar Orbiter Radial Alignment. The first radial alignment between Parker Solar Probe and Solar Orbiter spacecraft is used to investigate the evolution of solar wind turbulence in the inner heliosphere. Assuming ballistic propagation, two 1.5 hr intervals are tentatively identified as providing measurements of the same plasma parcels traveling from 0.1 to 1 au. Using magnetic field measurements from both spacecraft, the properties of turbulence in the two intervals are assessed. Magnetic spectral density, flatness, and high-order moment scaling laws are calculated. The Hilbert-Huang transform is additionally used to mitigate short sample and poor stationarity effects. Results show that the plasma evolves from a highly Alfvénic, less-developed turbulence state near the Sun, to fully developed and intermittent turbulence at 1 au. These observations provide strong evidence for the radial evolution of solar wind turbulence.

Keywords: Space plasmas, Magnetohydrodynamics, Interplanetary turbulence, Solar wind, Alfven waves