Sazuna/UAT_keywords huggingface dataset:
SDSS-IV MaNGA: Variations in the N/O-O/H Relation Bias Metallicity Gradient Measurements. In this Letter we use strong line calibrations of the N/O and O/H in Mapping Galaxies at Apache Point Observatory (MaNGA) galaxy survey spaxel data to explore the systematics introduced by variations in N/O on various strong-line metallicity diagnostics. We find radial variations in N/O at fixed O/H that correlate with total galaxy stellar mass and that can induce ∼40% systematic uncertainties in oxygen abundance gradients when nitrogen-dependent abundance calibrations are used. Empirically, we find that departures from the expected N/O are associated with variation in the local star formation efficiency, as predicted by recent chemical evolution models for galaxies, but we cannot rule out other processes such as radial migration also playing a role.

Keywords: Galaxy chemical evolution, Abundance ratios, Chemical abundances, Chemical enrichment, Metallicity
On the Possibility of GW190425 Being a Black Hole-Neutron Star Binary Merger. We argue that the kilonova/macronova associated with the gravitational-wave event GW190425 could have been bright enough to be detected if it was caused by the merger of a low-mass black hole (BH) and a neutron star (NS). Although tidal disruption occurs for such a low-mass BH is generally expected, the masses of the dynamical ejecta are limited to ≲10-3 M⊙, which is consistent with previous work in the literature. The remnant disk could be as massive as 0.05-0.1 M⊙, and the disk outflow of ∼0.01-0.03 M⊙ is likely to be driven by viscous or magnetohydrodynamic effects. The disk outflow may not be neutron-rich enough to synthesize an abundance of lanthanide elements, even in the absence of strong neutrino emitter, if the ejection is driven on the viscous timescale of ≳0.3 s. If this is the case, the opacity of the disk outflow is kept moderate, and a kilonova/macronova at the distance of GW190425 reaches a detectable brightness of 20-21 mag at 1 day after merger for most viewing angles. If some disk activity ejects the mass within ∼0.1 s, instead, lanthanide-rich outflows would be launched and the detection of emission becomes challenging. Future possible detections of kilonovae/macronovae from GW190425-like systems will disfavor the prompt collapse of binary NSs and a non-disruptive low-mass BH-NS binary associated with a small NS radius, whose mass ejection is negligible. The host-galaxy distance will constrain the viewing angle and deliver further information about the mass ejection.

Keywords: Neutron stars, Black holes, Compact binary stars, Gravitational wave sources, Time domain astronomy
Forecast of Major Solar X-Ray Flare Flux Profiles Using Novel Deep Learning Models. In this Letter, we present the application of a couple of novel deep learning models to the forecast of major solar X-ray flare flux profiles. These models are based on a sequence-to-sequence framework using long short-term memory cell and an attention mechanism. For this, we use Geostationary Operational Environmental Satellite 10 X-ray flux data from 1998 August to 2006 April. Seven hundred sixty events are used for training and 85 for testing. The models forecast 30 minutes of X-ray flux profiles during the rise phase of the solar flare with a minute time cadence. We evaluate the models using the 10-fold cross-validation and rms error (RMSE) based on flux profiles and RMSE based on its peak flux. For comparison we consider two simple deep learning models and four conventional regression models. Major results of this study are as follows. First, we successfully apply our deep learning models to the forecast of solar flare X-ray flux profiles, without any preprocessing to extract features from data. Second, our proposed models outperform the other models. Third, our models achieve better performance for forecasting X-ray flux profiles with low-peak fluxes than those with high-peak fluxes. Fourth, our models successfully predict flare duration with high correlations for both all cases and cases at peak times. Our study indicates that our deep learning models can be useful for forecasting time-series data in astronomy and space weather, even for impulsive events such as major flares.

Keywords: The Sun, Time series analysis, Solar x-ray flares
Does Gravity Fall Down? Evidence for Gravitational-wave Deflection along the Line of Sight to GW170817. We present a novel test of general relativity (GR): measuring the geometric component of the time delay due to gravitational lensing. GR predicts that photons and gravitational waves follow the same geodesic paths and thus experience the same geometric time delay. We show that for typical systems, the time delays are tens of seconds, and thus can dominate over astrophysical delays in the timing of photon emission. For the case of GW170817, we use a multi-plane lensing code to evaluate the time delay due to four massive halos along the line of sight. From literature mass and distance measurements of these halos, we establish at high confidence (significantly greater than $5\sigma $ ) that the gravitational waves of GW170817 underwent gravitational deflection to arrive within 1.7 s of the photons.

Keywords: Weak gravitational lensing, Gravitational deflection, Gravitational wave sources, Gravitational wave astronomy, Gravitational waves
GJ 1252 b: A 1.2 R<SUB>⊕</SUB> Planet Transiting an M3 Dwarf at 20.4 pc. We report the discovery of GJ 1252 b, a planet with a radius of 1.193 ± 0.074 ${R}_{\oplus }$ and an orbital period of 0.52 days around an M3-type star (0.381 ± 0.019 ${M}_{\odot }$ , 0.391 ± 0.020 ${R}_{\odot }$ ) located 20.385 ± 0.019 pc away. We use Transiting Exoplanet Survey Satellite (TESS) data, ground-based photometry and spectroscopy, Gaia astrometry, and high angular resolution imaging to show that the transit signal seen in the TESS data must originate from a transiting planet. We do so by ruling out all false-positive scenarios that attempt to explain the transit signal as originating from an eclipsing stellar binary. Precise Doppler monitoring also leads to a tentative mass measurement of 2.09 ± 0.56 M⊕. The host star proximity, brightness (V = 12.19 mag, K = 7.92 mag), low stellar activity, and the system's short orbital period make this planet an attractive target for detailed characterization, including precise mass measurement, looking for other objects in the system, and planet atmosphere characterization.

Keywords: Exoplanet astronomy, M dwarf stars, Exoplanets
Discovery of a Low-mass Companion Embedded in the Disk of the Young Massive Star MWC 297 with VLT/SPHERE. We report the discovery of a low-mass stellar companion around the young Herbig Be star MWC 297. We performed multi-epoch high-contrast imaging in the near-infrared with the Very Large Telescope (VLT)/Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument. The companion is found at a projected separation of 244.7 ± 13.2 au and a position angle of 176.4 ± 0.1 deg. The large separation supports formation via gravitational instability. From the spectrum, we estimate a mass of 0.1-0.5 M☉, the range conveying uncertainties in the extinction of the companion and in evolutionary models at young ages. The orbit coincides with a gap in the dust disk inferred from the spectral energy distribution. The young age (≲1 Myr) and mass ratio with the central star (∼0.01) makes the companion comparable to PDS 70 b, suggesting a relation between formation scenarios and disk dynamics.

Keywords: Ae stars, Star formation, Binary stars
Nine Localized Deviations from Keplerian Rotation in the DSHARP Circumstellar Disks: Kinematic Evidence for Protoplanets Carving the Gaps. We present evidence for localized deviations from Keplerian rotation, I.e., velocity "kinks," in 8 of the 18 circumstellar disks observed by the DSHARP program: DoAr 25, Elias 2-27, GW Lup, HD 143006, HD 163296, IM Lup, Sz 129, and WaOph 6. Most of the kinks are detected over a small range in both radial extent and velocity, suggesting a planetary origin, but for some of them foreground contamination prevents us from measuring their spatial and velocity extent. Because of the DSHARP limited spectral resolution and signal to noise in the 12CO J = 2-1 line, as well as cloud contamination, the kinks are usually detected in only one spectral channel, and will require confirmation. The strongest circumstantial evidence for protoplanets in the absence of higher spectral resolution data and additional tracers is that, upon deprojection, we find that all of the candidate planets lie within a gap and/or at the end of a spiral detected in dust continuum emission. This suggests that a significant fraction of the dust gaps and spirals observed by Atacama Large Millimeter/submillimeter Array in disks are caused by embedded protoplanets.

Keywords: Submillimeter astronomy, Protoplanetary disks, Planet formation
Systematic Variations of CO J = 2-1/1-0 Ratio and Their Implications in The Nearby Barred Spiral Galaxy M83. We present spatial variations of the CO J = 2-1/1-0 line ratio ( ${R}_{21/10}$ ) in the barred spiral galaxy M83 using Total Power Array (single-dish telescopes) data from the Atacama Large Millimeter/submillimeter Array. While the intensities of these two lines correlate tightly, ${R}_{21/10}$ varies over the disk, with a disk average ratio of 0.69, and shows the galactic center and a two-arm spiral pattern. It is high (≳0.7) in regions of high molecular gas surface density (Σmol), but ranges from low to high ratios in regions of low Σmol. The ratio correlates well with the spatial distributions and intensities of far-ultraviolet (FUV) and infrared (IR) emissions, with FUV being the best correlated. It also correlates better with the ratio of specific intensities at 70 and 350 μm, a proxy for dust temperature, than with the IR intensities. Taken together, these results suggest either a direct or indirect link between the dust heating by the interstellar radiation field and the condition of giant molecular clouds (GMCs), even though no efficient mechanism is known for a thermal coupling of dust and bulk gas in GMCs. We speculate that the large spread of ${R}_{21/10}$ in low Σmol regions, mostly at the downstream sides of spiral arms, may be due to the evolution of massive stars after spiral arm passage. Having in a late phase escaped from the spiral arms and their parental clouds, they may contribute to the dust heating by FUV and gas heating by cosmic rays produced by supernovae.

Keywords: Molecular gas, Interstellar medium, Spiral galaxies
Hyperbolic Meteoroids Impacting the Moon. Since the discovery of the Moon's asymmetric ejecta cloud, the origin of its sunward-canted density enhancement has not been well understood. We propose impact ejecta from meteoroids on hyperbolic trajectories (β-meteoroids) that hit the Moon's sunward side could explain this unresolved asymmetry. β-meteoroids are submicron in size, comparable to or smaller than the regolith particles they hit, and can impact the Moon at very high speeds ∼100 km s-1. Therefore, their impact regime may differ from the significantly larger and slower sporadic meteoroids responsible for generating the bulk of the lunar impact ejecta cloud. We compare lunar impact ejecta production to β-meteoroid fluxes observed by multiple spacecraft. If β-meteoroids are able to liberate similar sized submicron particles, orbital dust detector measurements from the Lunar Dust Experiment on board the Lunar Atmosphere and Dust Environment Explorer spacecraft only need to detect one ejecta grain out of every 106 β-meteoroid impacts to the lunar surface to explain the sunward asymmetry with this additional population. This finding suggests β-meteoroids may also contribute to the evolution of other airless surfaces in the inner solar system, and by extension, at exozodiacal systems.

Keywords: Impact phenomena, Ejecta, Interplanetary dust, Meteoroid dust clouds, Lunar impacts, Zodiacal cloud, Circumstellar dust
Accretion-driven Sources in Spatially Resolved Lyα Emitters. Lyα emission is a standard tracer of starburst galaxies at high redshift. However, a number of local Lyα emitters (LAEs) are X-ray sources, suggesting a possible origin of Lyα photons other than young, hot stars, and which may be active at much later ages relative to the parent starburst. Resolved, nearby LAEs offer the opportunity to discriminate between diffuse X-ray emission arising from supernova-heated gas, high-mass X-ray binaries (HMXBs), or low-luminosity active galactic nuclei (LLAGN). We examine archival X-ray imaging from Chandra and XMM-Newton for 11 galaxies with spatially resolved Lyα imaging to determine the luminosity, morphology, and spectral hardness of the X-ray sources. The data are consistent with 9 of the 12, bright Lyα sources being driven by luminous, &gt; ${10}^{40}\ \mathrm{erg}\ {{\rm{s}}}^{-1}$ X-ray sources. Half of the eight Chandra sources are unresolved. The data suggest that nuclear activity, whether from LLAGN or nuclear starbursts, may play an important role in Lyα emission. Our results also suggest a significant link between Lyα emission and HMXBs, ultraluminous X-ray sources, and/or LLAGN, which would imply that Lyα may be generated over timescales 1-2 orders of magnitude longer than produced by photoionization from OB stars. This highlights a critical need to quantify the relative contributions of different sources across cosmic time, to interpret Lyα observations and the resulting properties of distant galaxies.

Keywords: Ultraviolet sources, Starburst galaxies, High energy astrophysics, Emission line galaxies, Lyman-alpha galaxies, Low-luminosity active galactic nuclei, X-ray active galactic nuclei, Extragalactic astronomy
A New Mechanism for Maunder-like Solar Minima: Phase Synchronization Dynamics in a Simple Nonlinear Oscillator of Magnetohydrodynamic Rossby Waves. The long-term solar cycle variability and Grand solar minima remain open questions from a theoretical point of view. Recently, a growing basis of evidence points out to the role of the magnetic Rossby waves in the solar cycle. Here we present a simple deterministic model, based on a low-order spectral representation of the barotropic quasi-geostrophic-magnetohydrodynamic equations for the Solar tachocline. This model supports the idea of the long-term behavior of the solar activity as a result of nonlinear interaction of magnetic Rossby modes. Solutions show that Rossby waves undergo irregular switches between periods of high activity and periods of suppressed activity, resembling the Maunder minimum. Low-energy states in the model are associated with the synchronization of the dynamical phases of the waves. These irregular transitions in the amplitudes of the waves are reminiscent of the observed time series of the solar activity. This suggests that Maunder-like states arise from chaotic transitions between regimes with different degrees of organization in the system.

Keywords: Solar cycle, Magnetohydrodynamics, Alfven waves, Solar magnetic fields, Maunder minimum, Sunspot cycle
Shaping the Envelope of the Asymptotic Giant Branch Star W43A with a Collimated Fast Jet. One of the major puzzles in the study of stellar evolution is the formation process of bipolar and multipolar planetary nebulae. There is growing consensus that collimated jets create cavities with dense walls in the slowly expanding (10-20 km s-1) envelope ejected in previous evolutionary phases, leading to the observed morphologies. However, the launching of the jet and the way it interacts with the circumstellar material to create such asymmetric morphologies have remained poorly known. Here we present for the first time CO emission from the asymptotic giant branch star W43A that traces the whole stream of a jet, from the vicinity of its driving stellar system out to the regions where it shapes the circumstellar envelope. We found that the jet has a launch velocity of 175 km s-1 and decelerates to a velocity of 130 km s-1 as it interacts with circumstellar material. The continuum emission reveals a bipolar shell with a compact bright dot in the center that pinpoints the location of the driving source of the jet. The kinematical ages of the jet and the bipolar shell are equal, τ ∼ 60 yr, indicating that they were created simultaneously, probably by a common underlying mechanism, and in an extremely short time. These results provide key initial conditions for the theoretical models that aim to explain the formation of bipolar morphologies in the circumstellar envelopes of low- and intermediate-mass stars.

Keywords: Asymptotic giant branch stars, Stellar jets
Spontaneous Onset of Collisionless Magnetic Reconnection on an Electron Scale. Using particle-in-cell simulations, we investigate the onset of magnetic reconnection from a quiescent Harris current sheet in collisionless plasmas. After the current sheet is destabilized by the collisionless tearing mode instability, it proceeds to onset of reconnection, which manifests spontaneous thinning of current sheet and pileup of upstream magnetic flux. Once the current sheet thins to a critical thickness, about two electron inertial lengths, reconnection begins to grow explosively in this electron current sheet. This study shows that the spontaneous onset of collisionless magnetic reconnection is controlled by electron kinetics.

Keywords: Planetary magnetospheres, Solar magnetic reconnection, Heliosphere, Plasma physics
Upper Limit on the Dissipation of Gravitational Waves in Gravitationally Bound Systems. It is shown that a gravitationally bound system with a one-dimensional velocity dispersion σ can at most dissipate a fraction $\sim 36{\left(\sigma /c\right)}^{3}$ of the gravitational wave (GW) energy propagating through it, even if their dynamical time is shorter than the wave period. The limit is saturated for low-frequency waves propagating through a system of particles with a mean-free-path equal to the size of the system, such as hot protons in galaxy clusters, strongly interacting dark matter particles in halos, or massive black holes in clusters. For such systems with random motions and no resonances, the dissipated fraction, $\lesssim {10}^{-6}$ , does not degrade the use of GWs as cosmological probes. At high-wave frequencies, the dissipated fraction is additionally suppressed by the square of the ratio between the collision frequency and the wave frequency. The electromagnetic counterparts that result from the dissipation are too faint to be detectable at cosmological distances.

Keywords: Gravitational waves
Fast Luminous Blue Transients in the Reionization Era and Beyond. To determine the epoch of reionization precisely and to reveal the property of inhomogeneous reionization are some of the most important topics of modern cosmology. Existing methods to investigate reionization that use cosmic microwave background, Lyα emitters, quasars, or gamma-ray bursts have difficulties in terms of accuracy or event rate. We propose that recently discovered fast luminous blue transients (FLBTs) have potential as a novel probe of reionization. We study the detectability of FLBTs at the epoch of reionization with upcoming WFIRST Wide-Field Instrument, using a star formation rate (SFR) derived from galaxy observations and an event rate of FLBTs proportional to the SFR. We find that if FLBTs occur at a rate of 1% of the core-collapse supernova rate, 2 (0.3) FLBTs per year per deg2 at z &gt; 6 (z &gt; 8) can be detected by a survey with a limiting magnitude of 26.5 mag in the near-infrared band and a cadence of 10 days. We conclude that the WFIRST supernova deep survey can detect ∼20 FLBTs at the epoch of reionization in the near future.

Keywords: Early universe, Reionization, Transient sources, High energy astrophysics
Probing Cosmic-Ray Transport with Radio Synchrotron Harps in the Galactic Center. Recent observations with the MeerKAT radio telescope reveal a unique population of faint nonthermal filaments pervading the central molecular zone, a region rich in molecular gas near the Galactic center. Some of those filaments are organized into groups of almost parallel filaments, seemingly sorted by their length, so that their morphology resembles a harp with radio-emitting "strings." We argue that the synchrotron-emitting GeV electrons of these radio harps have been consecutively injected by the same source (a massive star or pulsar) into spatially intermittent magnetic fiber bundles within a magnetic flux tube or via time-dependent injection events. After escaping from this source, the propagation of cosmic-ray (CR) electrons inside a flux tube is governed by the theory of CR transport. We propose to use observations of radio harp filaments to gain insight into the specifics of CR propagation along magnetic fields of which there are two principle modes: CRs could either stream with self-excited magnetohydrodynamic waves or diffuse along the magnetic field. To disentangle these possibilities, we conduct hydrodynamical simulations of either purely diffusing or streaming CR electrons and compare the resulting brightness distributions to the observed synchrotron profiles of the radio harps. We find compelling evidence that CR streaming is the dominant propagation mode for GeV CRs in one of the radio harps. Observations at higher angular resolution should detect more radio harps and may help to disentangle projection effects of the possibly three-dimensional flux-tube structure of the other radio harps.

Keywords: Computational methods, Galactic center, Non-thermal radiation sources, Cosmic rays
No Massive Companion to the Coherent Radio-emitting M Dwarf GJ 1151. The recent detection of circularly polarized, long-duration (&gt;8 hr), low-frequency (∼150 MHz) radio emission from the M4.5 dwarf GJ 1151 has been interpreted as arising from a star-planet interaction via the electron cyclotron maser instability. The existence or parameters of the proposed planets have not been determined. Using 20 new HARPS-N observations, we put 99th-percentile upper limits on the mass of any close companion to GJ 1151 at $M\sin I\lt 5.6\,{M}_{\oplus }$ . With no stellar, brown dwarf, or giant planet companion likely in a close orbit, our data are consistent with detected radio emission emerging from a magnetic interaction between a short-period terrestrial-mass planet and GJ 1151 (https://github.com/benjaminpope/video).

Keywords: Radial velocity, Solar-planetary interactions, Magnetic fields
GW170817A as a Hierarchical Black Hole Merger. Despite the rapidly growing number of stellar-mass binary black hole mergers discovered through gravitational waves, the origin of these binaries is still not known. In galactic centers, black holes can be brought to each others' proximity by dynamical processes, resulting in mergers. It is also possible that black holes formed in previous mergers encounter new black holes, resulting in so-called hierarchical mergers. Hierarchical events carry signatures such as higher-than-usual black hole mass and spin. Here we show that the recently reported gravitational-wave candidate, GW170817A, could be the result of such a hierarchical merger. In particular, its chirp mass ∼40 M⊙ and effective spin of χeff ∼ 0.5 are the typically expected values from hierarchical mergers within the disks of active galactic nuclei. We find that the reconstructed parameters of GW170817A strongly favor a hierarchical merger origin over having been produced by an isolated binary origin (with an odds ratio of &gt; 103).

Keywords: Active galactic nuclei, Gravitational waves, Black holes