Sazuna/UAT_keywords huggingface dataset:
A Case of Simultaneous Star and Planet Formation. While it is widely accepted that planets are formed in protoplanetary disks, there is still much debate on when this process happens. In a few cases protoplanets have been directly imaged, but for the vast majority of systems, disk gaps and cavities—seen especially in dust continuum observations—have been the strongest evidence of recent or ongoing planet formation. We present Atacama Large Millimeter/submillimeter Array observations of a nearly edge-on (i = 75°) disk containing a giant gap seen in dust but not in 12CO gas. Inside the gap, the molecular gas has a warm (100 K) component coinciding in position with a tentative free-free emission excess observed with the Karl G. Jansky Very Large Array. Using 1D hydrodynamic models, we find the structure of the gap is consistent with being carved by a planet with 4-70 MJup. The coincidence of free-free emission inside the planet-carved gap points to the planet being very young and/or still accreting. In addition, the 12CO observations reveal low-velocity large-scale filaments aligned with the disk major axis and velocity coherent with the disk gas that we interpret as ongoing gas infall from the local interstellar medium. This system appears to be an interesting case where both a star (from the environment and the disk) and a planet (from the disk) are growing in tandem.

Keywords: Molecular gas, Dust continuum emission, Star formation, Protoplanetary disks, Circumstellar disks, Planet formation
Machine Learning as a Flaring Storm Warning Machine: Was a Warning Machine for the 2017 September Solar Flaring Storm Possible?. Machine learning is now one of the methodologies of choice for flare forecasting, and supervised techniques, in both their traditional and deep versions, are becoming more frequently used for prediction in this area of space weather. Most studies assess the prediction effectiveness of machine-learning methods by computing confusion matrices, which are typically highly non-diagonal, particularly in applications concerning the forecasting of X-class flares. The present study suggests that the reliability of the outcomes of a supervised machine-learning method could be better assessed by using it as a warning machine, sounding binary alerts unrolled over time, and by comparing the number of alerts sounded by the machine in specific time windows with the number of events actually observed in those time windows. Indeed, when applied to the prediction of the events associated with the 2017 September solar storm, a hybrid LASSO algorithm was able to sound alerts every day a flare actually occurred; it also identified the corresponding flare class. In addition, the machine was able to predict with some accuracy a reliable proxy of the energy budget daily released by magnetic reconnection during the entire course of the storm. Finally, the analysis shows that the combination of sparsity-enhancing machine learning and feature ranking could allow the identification of the prominent role that the Ising energy played as an active region property in the forecasting process.

Keywords: Solar active regions, Astronomy data modeling, Solar flares
Energy Supply for Heating the Slow Solar Wind Observed by Parker Solar Probe between 0.17 and 0.7 au. Energy supply sources for the heating process in the slow solar wind remain unknown. The Parker Solar Probe (PSP) mission provides a good opportunity to study this issue. Recently, PSP observations have found that the slow solar wind experiences stronger heating inside 0.24 au. Here for the first time we measure in the slow solar wind the radial gradient of the low-frequency breaks on the magnetic trace power spectra and evaluate the associated energy supply rate. We find that the energy supply rate is consistent with the observed perpendicular heating rate calculated based on the gradient of the magnetic moment. Based on this finding, one could explain why the slow solar wind is strongly heated inside 0.25 au but expands nearly adiabatically outside 0.25 au. This finding supports the concept that the energy added from the energy-containing range is transferred by an energy cascade process to the dissipation range, and then dissipates to heat the slow solar wind. The related issues for further study are discussed.

Keywords: Slow solar wind, Solar coronal heating, Interplanetary turbulence
GWSkyNet: A Real-time Classifier for Public Gravitational-wave Candidates. The rapid release of accurate sky localization for gravitational-wave (GW) candidates is crucial for multi-messenger observations. During the third observing run of Advanced LIGO and Advanced Virgo, automated GW alerts were publicly released within minutes of detection. Subsequent inspection and analysis resulted in the eventual retraction of a fraction of the candidates. Updates could be delayed by up to several days, sometimes issued during or after exhaustive multi-messenger follow-up campaigns. We introduce GWSkyNet, a real-time framework to distinguish between astrophysical events and instrumental artifacts using only publicly available information from the LIGO-Virgo open public alerts. This framework consists of a non-sequential convolutional neural network involving sky maps and metadata. GWSkyNet achieves a prediction accuracy of 93.5% on a testing data set.

Keywords: Gravitational wave astronomy, Convolutional neural networks, Observational astronomy
Evidence for Late-time Feedback from the Discovery of Multiphase Gas in a Massive Elliptical at z = 0.4. We report the first detection of multiphase gas within a quiescent galaxy beyond z ≈ 0. The observations use the brighter image of doubly lensed QSO HE 0047-1756 to probe the interstellar medium (ISM) of the massive ( ${M}_{\mathrm{star}}\approx {10}^{11}\,{M}_{\odot }$ ) elliptical lens galaxy at ${z}_{\mathrm{gal}}=0.408$ . Using Hubble Space Telescope's Cosmic Origins Spectrograph (COS), we obtain a medium-resolution FUV spectrum of the lensed QSO and identify numerous absorption features from H2 in the lens ISM at projected distance d = 4.6 kpc. The H2 column density is $\mathrm{log}\,N({{\rm{H}}}_{2})/{\mathrm{cm}}^{-2}={17.8}_{-0.3}^{+0.1}$ with a molecular gas fraction of ${f}_{{{\rm{H}}}_{2}}=2 \% \mbox{--}5 \% $ , roughly consistent with some local quiescent galaxies. The new COS spectrum also reveals kinematically complex absorption features from highly ionized species O VI and N V with column densities log N(O VI) $/{\mathrm{cm}}^{-2}=15.2\pm 0.1$ and log N(N V) $/{\mathrm{cm}}^{-2}=14.6\pm 0.1$ , among the highest known in external galaxies. Assuming the high-ionization absorption features originate in a transient warm (T ∼ 105 K) phase undergoing radiative cooling from a hot halo surrounding the galaxy, we infer a mass accretion rate of $\sim 0.5\mbox{--}1.5\,{M}_{\odot }\,{\mathrm{yr}}^{-1}$ . The lack of star formation in the lens suggests that the bulk of this flow is returned to the hot halo, implying a heating rate of $\sim {10}^{48}\,\mathrm{erg}\,{\mathrm{yr}}^{-1}$ . Continuous heating from evolved stellar populations (primarily SNe Ia but also winds from AGB stars) may suffice to prevent a large accumulation of cold gas in the ISM, even in the absence of strong feedback from an active nucleus.

Keywords: Galaxy formation, Quasar absorption line spectroscopy, Galaxy abundances, Circumgalactic medium, Elliptical galaxies
Three-dimensional Geometry of the Electron-scale Magnetic Hole in the Solar Wind. Electron-scale magnetic holes filled with high-energy electrons can provide a seed population of electrons in the magnetosphere and might play an important role in the interaction between the magnetosphere and solar wind. Theoretical studies have investigated their generation mechanisms based on the 1D or 2D geometry of the structure. However, the generation mechanism is still unclear. Here we report on the 3D geometry of the electron-scale magnetic hole in the solar wind based on the Magnetospheric Multiscale mission. We find that the cross section of the magnetic hole with a size of ∼0.2-0.6 ρi (ion gyroradius) is either circular or 2D sheet-like. Electron vortices exist in both kinds of cross sections. The ellipse is a possible candidate for the geometry of the magnetic hole in the plane including its axis. Surprisingly, such an elliptical geometry suggests that the axial lengths of all our selected magnetic holes are ∼1-2 ρi. This 3D geometry might shed some light on the generation mechanism and role of the electron-scale magnetic hole in the astrophysical plasma.

Keywords: Planetary magnetospheres, Solar wind
Detection of Dynamical Instability in Titan's Thermospheric Jet. Similar to Earth, Saturn's largest moon, Titan, possesses a system of high-altitude zonal winds (or jets) that encircle the globe. Using the Atacama Large Millimeter/submillimeter Array (ALMA) in 2016 August, Lellouch et al. discovered an equatorial jet at much higher altitudes than previously known, with a surprisingly fast speed of up to ∼340 m s-1; however, the origin of such high velocities is not yet understood. We obtained spectrally and spatially resolved ALMA observations in 2017 May to map Titan's 3D global wind field and compare our results with a re-analysis of the 2016 August data. Doppler wind velocity maps were derived in the altitude range ∼300-1000 km (from the upper stratosphere to the thermosphere). At the highest thermospheric altitudes, a 47% reduction in the equatorial zonal wind speed was measured over the 9 month period (corresponding to Ls = 82°-90° on Titan). This is interpreted as being due to a dramatic slowing and loss of confinement (broadening) of the recently discovered thermospheric equatorial jet, as a result of dynamical instability. These unexpectedly rapid changes in the upper-atmospheric dynamics are consistent with strong variability of the jet's primary driving mechanism.

Keywords: Radio interferometry, Doppler imaging, Atmospheric circulation
The Stellar Merger Scenario for Black Holes in the Pair-instability Gap. The recent detection of GW190521 stimulated ideas on how to populate the predicted black hole (BH) pair-instability (PI) mass gap. One proposal is the dynamical merger of two stars below the PI regime forming a star with a small core and an oversized envelope. We outline the main challenges this scenario faces to form one BH in the gap. In particular, the core needs to avoid growing during the merger, and the merger product needs to retain enough mass, including in the subsequent evolution, and at core collapse (CC). We explore this scenario with detailed stellar evolution calculations, starting with ad hoc initial conditions enforcing no core growth during the merger. We find that these massive merger products are likely to be helium-rich and spend most of their remaining lifetime within regions of instabilities in the Herzsprung-Russell diagram, such as luminous blue variable eruptions. An energetic estimate of the amount of mass loss neglecting the back reaction of the star suggests that the total amount of mass that can be removed at low metallicity is ≲1 M⊙. This is small enough that at CC our models are retaining sufficient mass to form BHs in the PI gap similar to the recent ones detected by LIGO/Virgo. However, mass loss at the time of merger, the resulting core structure, and the mass loss at CC still need to be quantified for these models to confirm the viability of this scenario.

Keywords: Massive stars, Black holes, Luminous blue variable stars, Stellar mergers
Constraining the Milky Way Mass with Its Hot Gaseous Halo. We propose a novel method to constrain the Milky Way (MW) mass ${M}_{\mathrm{vir}}$ with its corona temperature observations. For a given corona density profile, one can derive its temperature distribution assuming a generalized equilibrium model with nonthermal pressure support. While the derived temperature profile decreases substantially with radius, the X-ray-emission-weighted average temperature, which depends most sensitively on ${M}_{\mathrm{vir}}$ , is quite uniform toward different sight lines, consistent with X-ray observations. For a Navarro-Frenk-White (NFW) total matter distribution, the corona density profile should be cored, and we constrain ${M}_{\mathrm{vir}}=(1.19\mbox{--}2.95)\times {10}^{12}{M}_{\odot }$ . For a total matter distribution contributed by an NFW dark matter profile and central baryons, the corona density profile should be cuspy and ${M}_{\mathrm{vir},\mathrm{dm}}=(1.34\mbox{--}5.44)\times {10}^{12}{M}_{\odot }$ . Nonthermal pressure support leads to even higher values of ${M}_{\mathrm{vir}}$ , while a lower MW mass may be possible if the corona is accelerating outward. This method is independent of the total corona mass, its metallicity, and temperature at very large radii.

Keywords: X-ray astronomy, Galaxy dark matter halos, Hydrodynamics, Circumgalactic medium, Galaxy masses, Milky Way Galaxy, Milky Way mass
Fast Radio Burst Breakouts from Magnetar Burst Fireballs. The recent discovery of a Mega-Jansky radio burst occurring simultaneously with short X-ray bursts from the Galactic magnetar (strongly magnetized neutron star (NS)) SGR 1935+2154 is a smoking gun for the hypothesis that some cosmological fast radio bursts (FRBs) arise from magnetar bursts. We argue that the X-ray bursts with high temperature T ≳ 30 keV entail an electron-positron (e±) outflow from a trapped-expanding fireball, polluting the NS magnetosphere before the FRB emission. The e± outflow is opaque to induced Compton scatterings of FRB photons, and is strongly Compton-dragged by the X-ray bursts. Nevertheless, the FRB photons can break out of the e± outflow with radiation forces if the FRB emission radius is larger than a few tens of NS radii. A FRB is choked if the FRB is weaker or the X-ray bursts are stronger, possibly explaining why there are no FRBs with giant flares and no detectable X-ray bursts with weak FRBs. We also speculate that the e± outflow may be inevitable for FRBs, solving the problem of why the FRBs occur only with high-T X-ray bursts. The breakout physics is important for constraining the emission mechanism and electromagnetic counterparts to future FRBs.

Keywords: Relativistic mechanics, Pulsars, Non-thermal radiation sources, Magnetars, X-ray bursts, Radio transient sources
Energy Conversion between Ions and Electrons through Ion Cyclotron Waves and Embedded Ion-scale Rotational Discontinuity in Collisionless Space Plasmas. Wave-particle interaction is a fundamental process in collisionless plasma, which results in the redistribution of energy between plasma waves and particle species. The analysis of high-resolution Magnetospheric Multiscale plasma and magnetic field data directly reveals the energy exchange between electromagnetic energy, particle bulk kinetic energy, and thermal kinetic energy in magnetosheath turbulence. This work focuses on the energy transfer associated with ion cyclotron waves (ICWs) and embedded rotational discontinuity (RD). We find that (1) the particle kinetic energy of ions is converted into electromagnetic energy; (2) the electrons are gaining energy from electromagnetic fields, having significant electron heating in the parallel direction around the RD; (3) the ICWs and RD connect and redistribute energy between ions and electrons in the postshock downstream sheath region; and (4) the interactions between pressure tensor and strain tensor redistribute the ion and electron bulk and thermal kinetic energies, but less significantly than direct field-particle interaction by one order of magnitude in the ICW turbulence with weak compressibility, in the sense that ${\left(d| {\boldsymbol{B}}| /| {\boldsymbol{B}}| \right)}^{2}\lt {10}^{-2}$ , ${\left(d{\rm{N}}/{\rm{N}}\right)}^{2}\lt {10}^{-2}$ .

Keywords: Interplanetary turbulence, Space plasmas, Solar wind
Recombination-independent Determination of the Sound Horizon and the Hubble Constant from BAO. The Hubble tension and attempts to resolve it by modifying the physics of (or at) recombination motivate finding ways to determine H0 and the sound horizon at the epoch of baryon decoupling rd in ways that rely neither on a recombination model nor on late-time Hubble data. In this work, we investigate what one can learn from the current and future BAO data when treating rd and H0 as independent free parameters. It is well known that baryon acoustic oscillations (BAOs) give exquisite constraints on the product rdH0. We show here that imposing a moderate prior on Ωmh2 breaks the degeneracy between rd and H0. Using the latest BAO data, including the recently released the extended Baryon Oscillation Spectroscopic Survey Data Release 16, along with a Ωmh2 prior based on the Planck best-fit Λ cold dark matter (ΛCDM) model, we find rd = 143.7 ± 2.7 Mpc and H0 = 69.6 ± 1.8 km s-1 Mpc-1. BAO data prefers somewhat lower rd and higher H0 than those inferred from Planck data in a ΛCDM model. We find similar values when combing BAO with the Pantheon supernovae, the Dark Energy Survey Year 1 galaxy weak lensing, Planck or SPTPol cosmic microwave background lensing, and the cosmic chronometer data. We perform a forecast for the Dark Energy Spectroscopic Instrument (DESI) and find that, when aided with a moderate prior on Ωmh2, DESI will measure rd and H0 without assuming a recombination model with an accuracy surpassing the current best estimates from Planck.

Keywords: Cosmology, Recombination (cosmology), Baryon acoustic oscillations, Hubble constant
Hiding Signatures of Gravitational Instability in Protoplanetary Disks with Planets. We carry out three-dimensional smoothed particle hydrodynamics simulations to show that a migrating giant planet strongly suppresses the spiral structure in self-gravitating disks. We present mock Atacama Large Millimeter/submillimeter Array (ALMA) continuum observations that show that in the absence of a planet, spiral arms due to gravitational instability are easily observed. Whereas in the presence of a giant planet, the spiral structures are suppressed by the migrating planet resulting in a largely axisymmetric disk with a ring and gap structure. Our modeling of the gas kinematics shows that the planet's presence could be inferred, for example, using optically thin 13C16O. Our results show that it is not necessary to limit the gas mass of disks by assuming high dust-to-gas mass ratios in order to explain a lack of spiral features that would otherwise be expected in high-mass disks.

Keywords: Protoplanetary disks
P/2019 LD2 (ATLAS): An Active Centaur in Imminent Transition to the Jupiter Family. The recently discovered object P/2019 LD2 (by the Asteroid Terrestrial-impact Last Alert System) was initially thought to be a Jupiter Trojan asteroid, until dynamical studies and the appearance of persistent cometary activity revealed that this object is actually an active Centaur. However, the dynamical history, thermal environment, and impact of such environments on the activity of 2019 LD2 are poorly understood. Here we conduct dynamical simulations to constrain its orbital history and resulting thermal environment over the past 3000 yr. We find that 2019 LD2 is currently in the vicinity of a dynamical "Gateway" that facilitates the majority of transitions from the Centaur population into the Jupiter Family of Comets (JFC population). Our calculations show that it is unlikely to have spent significant amounts of time in the inner solar system, suggesting that its nucleus is relatively pristine in terms of physical, chemical, and thermal processing through its history. This could explain its relatively high level of distant activity as a recently activated primordial body. Finally, we find that the median frequency of transition from the Gateway population into the JFC population varies from once every ∼3 yr to less than once every 70 yr, if 2019 LD2's nucleus is ∼1 km in radius or greater than 3 km in radius. Forward modeling of 2019 LD2 shows that it will transition into the JFC population in 2063, representing the first known opportunity to observe the evolution of an active Centaur nucleus as it experiences this population-defining transition.

Keywords: Centaur group, Orbits, Short period comets, Comets, Astrophysical fluid dynamics, Comet interiors
NICER View of the 2020 Burst Storm and Persistent Emission of SGR 1935+2154. We report on NICER observations of the magnetar SGR 1935+2154, covering its 2020 burst storm and long-term persistent emission evolution up to ∼90 days postoutburst. During the first 1120 s taken on April 28 00:40:58 UTC, we detect over 217 bursts, corresponding to a burst rate of &gt;0.2 bursts s-1. Three hours later, the rate was 0.008 bursts s-1, remaining at a comparatively low level thereafter. The T90 burst duration distribution peaks at 840 ms; the distribution of waiting times to the next burst is fit with a lognormal with an average of 2.1 s. The 1-10 keV burst spectra are well fit by a blackbody, with an average temperature and area of kT = 1.7 keV and R2 = 53 km2. The differential burst fluence distribution over ∼3 orders of magnitude is well modeled with a power-law form dN/dF ∝ F-1.5±0.1. The source persistent emission pulse profile is double-peaked hours after the burst storm. We find that the burst peak arrival times follow a uniform distribution in pulse phase, though the fast radio burst associated with the source aligns in phase with the brighter peak. We measure the source spin-down from heavy-cadence observations covering days 21-39 postoutburst, $\dot{\nu }=-3.72(3)\times {10}^{-12}$ Hz s-1, a factor of 2.7 larger than the value measured after the 2014 outburst. Finally, the persistent emission flux and blackbody temperature decrease rapidly in the early stages of the outburst, reaching quiescence 40 days later, while the size of the emitting area remains unchanged.

Keywords: Neutron stars, Magnetars, Soft gamma-ray repeaters
Investigating the Hubble Constant Tension: Two Numbers in the Standard Cosmological Model. The current Hubble constant tension is usually presented by comparing constraints on H0 only. However, the postrecombination background cosmic evolution is determined by two parameters in the standard ΛCDM model, the Hubble constant (H0) and today's matter energy fraction (Ωm). If we therefore compare all constraints individually in the H0-Ωm plane, (1) various constraints can be treated as independently as possible, (2) single-sided constraints are easier to consider, (3) compatibility among different constraints can be viewed in a more robust way, (4) the model dependence of each constraint is clear, and (5) whether or not a nonstandard model is able to reconcile all constraints in tension can be seen more effectively. We perform a systematic comparison of different constraints in the H0-Ωm space based on a flat ΛCDM model, treating them as separately as possible. Constraints along different degeneracy directions consistently overlap in one region of the space, with the local measurement from Cepheid variable-calibrated supernovae being the most outlying, followed by the time-delay strong-lensing result. Considering the possibility that some nonstandard physics may reconcile the constraints, we provide a general discussion of nonstandard models with modifications at high, mid, or low redshifts and the effect of local environmental factors. Due to the different responses of individual constraints to a modified model, it is not easy for nonstandard models to reconcile all constraints if none of them have unaccounted-for systematic effects.

Keywords: Cosmology, Cosmological models, Hubble constant, Expanding universe