Sazuna/UAT_keywords huggingface dataset:
Comet C/2017 S3 (PanSTARRS): Outbursts and Disintegration. The Solar Wind ANisotropies (SWAN) all-sky hydrogen Lyα camera on the SOlar and Heliospheric Observer satellite observed the hydrogen coma of comet C/2017 S3 (PanSTARRS) for the last month of its activity from 2018 July 4 to August 4 and what appears to have been its final disintegration just 11 days before its perihelion on August 15. The hydrogen coma indicated water production had a small outburst on July 8 at a heliocentric distance of 1.1 au and then a much larger one on July 20 at 0.8 au. Over the following two weeks the water production dropped by more than a factor of 10 after which it was no longer detectable. The behavior is reminiscent of comet C/1999 S4 (LINEAR) in 2000, which had a few small outbursts on its inbound orbit and a major outburst at a heliocentric distance of about 0.8 au, which was close to its perihelion, followed by its complete disintegration that was documented by several sets of observations including SWAN. C/2017 S3 (PanSTARRS), however, had a much larger water production rate than C/1999 S4 (LINEAR). Here we estimate the size of the nucleus of C/2017 S3 just before its final outburst and apparent disintegration were estimated using the total amount of water produced during its last weeks for a range of values of the refractory/ice ratio in the nucleus. We also determine the size distribution of the disintegrating particles as the comet faded.

Keywords: Long period comets, Comets, Comae
Magnetohydrodynamic Seismology of Quiet Solar Active Regions. The ubiquity of recently discovered low-amplitude decayless kink oscillations of plasma loops allows for the seismological probing of the corona on a regular basis. In particular, in contrast to traditionally applied seismology that is based on the large-amplitude decaying kink oscillations excited by flares and eruptions, decayless oscillations can potentially provide the diagnostics necessary for their forecasting. We analyzed decayless kink oscillations in several distinct loops belonging to active region NOAA 12107 on 2010 July 10 during its quiet time period, when it was observed on the west limb in extreme ultraviolet by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. The oscillation periods were estimated with the use of the motion magnification technique. The lengths of the oscillating loops were determined within the assumption of its semicircular shape by measuring the position of their footpoints. The density contrast in the loops was estimated from the observed intensity contrast accounting for the unknown spatial scale of the background plasma. The combination of those measurements allows us to determine the distribution of kink and Alfvén speeds in the active region. Thus, we demonstrate the possibility of obtaining seismological information about coronal active regions during the quiet periods of time.

Keywords: Solar active region magnetic fields, Solar coronal loops, Solar coronal waves, Solar magnetic fields, Solar oscillations, Solar coronal seismology
An Ideal Testbed for Planet-Disk Interaction: Two Giant Protoplanets in Resonance Shaping the PDS 70 Protoplanetary Disk. While numerical simulations have been playing a key role in the studies of planet-disk interaction, testing numerical results against observations has been limited so far. With the two directly imaged protoplanets embedded in its circumstellar disk, PDS 70 offers an ideal testbed for planet-disk interaction studies. Using two-dimensional hydrodynamic simulations we show that the observed features can be well explained with the two planets in formation, providing strong evidence that previously proposed theories of planet-disk interaction are in action, including resonant migration, particle trapping, size segregation, and filtration. Our simulations suggest that the two planets are likely in 2:1 mean motion resonance and can remain dynamically stable over million-year timescales. The growth of the planets at 10-8-10-7 M Jup yr-1, rates comparable to the estimates from Hα observations, does not destabilize the resonant configuration. Large grains are filtered at the gap edge and only small, (sub-)μm grains can flow to the circumplanetary disks (CPDs) and the inner circumstellar disk. With the submillimeter continuum ring observed outward of the two directly imaged planets, PDS 70 provides the first observational evidence of particle filtration by gap-opening planets. The observed submillimeter continuum emission at the vicinity of the planets can be reproduced when (sub-)μm grains survive over multiple CPD gas viscous timescales and accumulate therein. One such possibility is if (sub-)μm grains grow in size and remain trapped in pressure bumps, similar to what we find happening in circumstellar disks. We discuss potential implications to planet formation in the solar system and mature extrasolar planetary systems.

Keywords: Hydrodynamical simulations, Planet formation, Circumstellar disks
Rapid Escape of Ultra-hot Exoplanet Atmospheres Driven by Hydrogen Balmer Absorption. Atmospheric escape is key to explaining the long-term evolution of planets in our solar system and beyond, and in the interpretation of atmospheric measurements. Hydrodynamic escape is generally thought to be driven by the flux of extreme-ultraviolet photons that the planet receives from its host star. Here, we show that the escape from planets orbiting hot stars proceeds through a different yet complementary process: drawing its energy from the intense near-ultraviolet emission of the star that is deposited within an optically thin, high-altitude atmospheric layer of hydrogen excited into the lower state of the Balmer series. The ultra-hot exoplanet KELT-9b likely represents the first known instance of this Balmer-driven escape. In this regime of hydrodynamic escape, the near-ultraviolet emission from the star is more important at determining the planet mass loss than the extreme-ultraviolet emission, and uncertainties in the latter become less critical. Further, we predict that gas exoplanets around hot stars may experience catastrophic mass loss when they are less massive than 1-2 Jupiter masses and closer in than KELT-9b, thereby challenging the paradigm that all large exoplanets are stable to atmospheric escape. We argue that extreme escape will affect the demographics of close-in exoplanets orbiting hot stars.

Keywords: Exoplanet evolution, Aeronomy, Radiative transfer, Exoplanet atmospheres
Fast Extragalactic X-Ray Transients from Gamma-Ray Bursts Viewed Far Off-axis. The observed light curves and estimated sky rate of fast extragalactic X-ray transients (XRTs) discovered in archival Chandra data indicate that they belong to two distinct XRT populations. The first population of relatively short duration pulses, which typically last less than few minutes seems to be pulses of X-ray flashes, which are nearby long-duration gamma-ray bursts viewed from far off-axis. The second population of much longer pulses, which typically last hours, seems to be the early-time isotropic afterglows of short gamma-ray bursts that are beamed away from Earth, as was shown in a previous paper.

Keywords: X-ray transient sources
Quantifying the Effect of Black Hole Feedback from the Central Galaxy on the Satellite Populations of Groups and Clusters. Supermassive black holes are fundamental ingredients in our theoretical understanding of galaxy formation. They are likely the only sources energetic enough to regulate star formation within massive dark matter halos, but observational evidence of this process remains elusive. The effect of black hole feedback is expected to be a strong function of halo mass, and galaxy groups and clusters are among the most massive structures in the universe. At fixed halo mass, we find an enhanced fraction of quiescent satellite galaxies and a hotter X-ray intragroup and intracluster medium (IGM/ICM) in those groups and clusters hosting more massive black holes in their centers. These results indicate that black hole feedback makes quenching processes more efficient through a cumulative heating of the gaseous IGM and ICM.

Keywords: Galaxy clusters, Supermassive black holes, Star formation, Galaxy evolution, Galaxy quenching, Intracluster medium
No Snowball on Habitable Tidally Locked Planets with a Dynamic Ocean. Terrestrial planets orbiting within the habitable zones of M-stars are likely to become tidally locked in a 1:1 spin:orbit configuration and are prime targets for future characterization efforts. An issue of importance for the potential habitability of terrestrial planets is whether they could experience Snowball events (periods of global glaciation). Previous work using an intermediate-complexity atmospheric Global Climate Model (GCM) with no ocean heat transport suggested that tidally locked planets would smoothly transition to a Snowball, in contrast with Earth, which has bifurcations and hysteresis in climate state associated with global glaciation. In this Letter, we use a coupled ocean-atmosphere GCM (ROCKE-3D) to model tidally locked planets with no continents. We chose this configuration in order to consider a case that we expect to have high ocean heat transport. We show that including ocean heat transport does not reintroduce the Snowball bifurcation. An implication of this result is that a tidally locked planet in the habitable zone is unlikely to be found in a Snowball state for a geologically significant period of time.

Keywords: Exoplanets, Exoplanet astronomy, Astrobiology, Habitable planets, Exoplanet atmospheres
Signatures of a Planet-Planet Impacts Phase in Exoplanetary Systems Hosting Giant Planets. Exoplanetary systems host giant planets on substantially noncircular, close-in orbits. We propose that these eccentricities arise in a phase of giant impacts, analogous to the final stage of solar system assembly that formed Earth’s Moon. In this scenario, the planets scatter each other and collide, with corresponding mass growth as they merge. We numerically integrate an ensemble of systems with varying total planet mass, allowing for collisional growth, to show that (1) the high-eccentricity giants observed today may have formed preferentially in systems of higher initial total planet mass, and (2) the upper bound on the observed giant planet eccentricity distribution is consistent with planet-planet scattering. We predict that mergers will produce a population of high-mass giant planets between 1 and 8 au from their stars.

Keywords: Planetary system formation, Exoplanet formation, Exoplanet dynamics
Vapor Drainage in the Protolunar Disk as the Cause for the Depletion in Volatile Elements of the Moon. Lunar rocks are severely depleted in moderately volatile elements (MVEs) such as Rb, K, and Zn relative to Earth. Identifying the cause of this depletion is important for understanding how the Earth-Moon system evolved in the aftermath of the Moon-forming giant impact. We measured the Rb isotopic compositions of lunar and terrestrial rocks to understand why MVEs are depleted in the Moon. Combining our new measurements with previous data reveals that the Moon has an 87Rb/85Rb ratio higher than Earth by +0.16 ± 0.04‰. This isotopic composition is consistent with evaporation of Rb into a vapor medium that was ∼99% saturated. Evaporation under this saturation can also explain the previously documented isotopic fractionations of K, Ga, Cu, and Zn of lunar rocks relative to Earth. We show that a possible setting for achieving the same saturation upon evaporation of elements with such diverse volatilities is through viscous drainage of a partially vaporized protolunar disk onto Earth. In the framework of an α-disk model, the α-viscosity needed to explain the ∼99% saturation calculated here is 10-3-10-2, which is consistent with a vapor disk where viscosity is controlled by magnetorotational instability.

Keywords: Lunar origin, Cosmochemistry, Earth-moon system
Investigating Particle Acceleration in the Wolf-Rayet Bubble G2.4+1.4. The supersonic winds produced by massive stars carry a large amount of kinetic power. In numerous scenarios such winds have been proven to produce shocks in which relativistic particles are accelerated emitting nonthermal (NT) radiation. Here, we report the first detection of NT emission from a single stellar bubble, G2.4+1.4, associated with a WO star. We observed this source with the upgraded Giant Meterwave Radio Telescope in Band 4 (550-850 MHz) and Band 5 (1050-1450 MHz). We present intensity and spectral index maps for this source that are consistent with synchrotron emission (average spectral index, α = -0.83 ± 0.10). The fraction of the available kinetic wind power that is converted into cosmic-ray acceleration is estimated to be of the order of a few percent. This finding constitutes an observational breakthrough and gives new insight on the NT physical processes taking place in the environments of isolated massive stars. In particular, our results show that non-runaway isolated massive stars are capable of accelerating relativistic particles and are therefore confirmed as sources of Galactic cosmic rays.

Keywords: Stellar wind bubbles, Radio continuum emission, Non-thermal radiation sources, Interstellar medium, Wolf-Rayet stars
Ram-pressure Stripping of a Kicked Hill Sphere: Prompt Electromagnetic Emission from the Merger of Stellar Mass Black Holes in an AGN Accretion Disk. Accretion disks around supermassive black holes (SMBHs) are promising sites for stellar mass black hole (BH) mergers due to mass segregation and merger acceleration by disk gas torques. Here we show that a gravitational-wave (GW) kick at BH merger causes ram-pressure stripping of gas within the BH Hill sphere. If R H ≥ H, the disk height, an off-center UV flare at a BH ∼ 103 r  g , emerges within t UV ∼ O(2 days)(a BH/103 r  g )(M SMBH/108 M ⊙)(v kick/102 km s-1) postmerger and lasts O(R H/v kick) ∼ O(5t UV). The flare emerges with luminosity O(1042erg s-1)(t UV/2days)-1(M Hill/1M ⊙)(v kick/102 km s-1)2. Active galactic nucleus optical/UV photometry is altered and asymmetric broad emission line profiles can develop after weeks. If R H &lt; H, detectability depends on disk optical depth. Follow-up by large optical sky surveys is optimized for small GW error volumes and for Laser Interferometer Gravitational-Wave Observatory/Virgo triggers &gt;50M ⊙.

Keywords: Gravitational wave astronomy, Gravitational waves, Active galactic nuclei, Black holes
Nearly all Massive Quiescent Disk Galaxies Have a Surprisingly Large Atomic Gas Reservoir. The massive galaxy population above the characteristic Schechter mass M * ≈ 1010.6 {M}⊙  contributes to about half of the total stellar mass in the local universe. These massive galaxies usually reside in hot dark matter halos above the critical shock-heating mass ∼1012 {M}⊙ , where the external cold gas supply to these galaxies is expected to be suppressed. When galaxies run out of their cold gas reservoir, they become dead and quiescent. Therefore, massive quiescent galaxies living in hot halos are commonly believed to be gas-poor. Based on the data from SDSS, ALFALFA, GASS, and COLD GASS surveys, here we show that the vast majority of the massive, quiescent, central disk galaxies in the nearby universe have a remarkably large amount of cold atomic hydrogen gas, surprisingly similar to star-forming galaxies. Both star-forming and quiescent disk galaxies show identical symmetric double-horn H I spectra, indicating similar regularly rotating H I disks. Relative to their star-forming counterparts, massive quiescent central disk galaxies are quenched because of their significantly reduced molecular gas content, lower dust content, and lower star formation efficiency. Our findings reveal a new picture, which clearly demonstrates the detailed star formation quenching process in massive galaxies and provides a stringent constraint on the physical mechanism of quenching.

Keywords: Galaxy quenching, Galaxy evolution, Interstellar medium, Interstellar atomic gas
Parallel-propagating Fluctuations at Proton-kinetic Scales in the Solar Wind Are Dominated By Kinetic Instabilities. We use magnetic helicity to characterize solar wind fluctuations at proton-kinetic scales from Wind observations. For the first time, we separate the contributions to helicity from fluctuations propagating at angles quasi-parallel and oblique to the local mean magnetic field, {{\boldsymbol{B}}}0. We find that the helicity of quasi-parallel fluctuations is consistent with Alfvén-ion cyclotron and fast magnetosonic-whistler modes driven by proton temperature anisotropy instabilities and the presence of a relative drift between α-particles and protons. We also find that the helicity of oblique fluctuations has little dependence on proton temperature anisotropy and is consistent with fluctuations from the anisotropic turbulent cascade. Our results show that parallel-propagating fluctuations at proton-kinetic scales in the solar wind are dominated by proton temperature anisotropy instabilities and not the turbulent cascade. We also provide evidence that the behavior of fluctuations at these scales is independent of the origin and macroscopic properties of the solar wind.

Keywords: Slow solar wind, Space plasmas, Heliosphere, Plasma physics, Interplanetary turbulence, Fast solar wind, Solar wind, Plasma astrophysics, Alfven waves
An Improved Treatment of Neutral Sheet Drift in the Inner Heliosphere. Drifts due to the curvature and gradients in the heliospheric magnetic field, as well as along the heliospheric current sheet, have long been known to play a significant role in the transport of galactic cosmic rays. Recently, there has been greater interest in the role these drifts play in the transport of solar energetic particles. This study proposes an approach to modeling particle drift velocities in particle transport codes that, while being relatively simple to implement and computationally inexpensive, also models drift effects accurately across a broader range of energies than previous approaches.

Keywords: Solar energetic particles, Heliosphere, Cosmic rays
A Galaxy-targeted Search for the Optical Counterpart of the Candidate NS-BH Merger S190814bv with Magellan. On 2019 August 14 the Laser Interferometer Gravitational Wave Observatory (LIGO) and the Virgo gravitational wave interferometer announced the detection of a binary merger, S190814bv, with a low false alarm rate of about 1 in 1.6 × 1025 yr, a distance of 267 ± 52 Mpc, a 90% (50%) localization region of about 23 (5) deg2, and a probability of being a neutron star-black hole (NS-BH) merger of &gt;99%. The LIGO/Virgo Collaboration (LVC) defines NS-BH such that the lighter binary member has a mass of &lt;3 M ☉ and the more massive one has &gt;5 M ☉, and this classification is in principle consistent with a BH-BH merger depending on the actual upper mass cutoff for neutron stars. Additionally, the LVC designated a probability that the merger led to matter outside the final BH remnant of &lt;1%, suggesting that an electromagnetic (EM) counterpart is unlikely. Here we report our optical follow-up observations of S190814bv using the Magellan Baade 6.5 m telescope to target all 96 galaxies in the Galaxy List for the Advanced Detector Era catalog within the 50% localization volume (representing about 70% of the integrated luminosity within this region). No counterpart was identified to a median 3σ limiting magnitude of i = 22.2 (M  i  ≈ -14.9 mag), comparable to the brightness of the optical counterpart of the binary neutron star merger GW170817 at the distance of S190814bv; similarly, we can rule out an on-axis jet typical of short GRBs. However, we cannot rule out other realistic models, such as a kilonova with only ∼0.01 M ☉ of lanthanide-rich material, or an off-axis jet with a viewing angle of θ obs ≳ 15°.

Keywords: Neutron stars, Observational astronomy, Gravitational waves, Astrophysical black holes
Spiral Structure in the Gas Disk of TW Hya. We report the detection of spiral substructure in both the gas velocity and temperature structure of the disk around TW Hya, suggestive of planet-disk interactions with an unseen planet. Perturbations from Keplerian rotation tracing out a spiral pattern are observed in the SE of the disk, while significant azimuthal perturbations in the gas temperature are seen in the outer disk, outside 90 au, extending the full azimuth of the disk. The deviation in velocity is either Δv  ϕ /v kep ∼ 0.1 or Δv  z /v kep ∼ 0.01 depending on whether the perturbation is in the rotational or vertical direction, while radial perturbations can be ruled out. Deviations in the gas temperature are ±4 K about the azimuthally averaged profile, equivalent to deviations of ΔT gas/T gas ∼ 0.05. Assuming all three structures can be described by an Archimedean spiral, measurements of the pitch angles of both velocity and temperature spirals show a radially decreasing trend for all three, ranging from 9° at 70 au, dropping to 3° at 200 au. Such low pitch-angled spirals are not readily explained through the wake of an embedded planet in the location of previously reported at 94 au, but rather require a launching mechanism that results in much more tightly wound spirals. Molecular emission tracing distinct heights in the disk is required to accurately distinguish between spiral launching mechanisms.

Keywords: Interferometry, Protoplanetary disks, Planet formation, Circumstellar disks
Reynolds Number and Intermittency in the Expanding Solar Wind: Predictions Based on Voyager Observations. The large-scale features of the solar wind are examined in order to predict small-scale features of turbulence in unexplored regions of the heliosphere. The strategy is to examine how system size, or effective Reynolds number Re, varies, and then how this quantity influences observable statistical properties, including intermittency properties of solar wind turbulence. The expectation based on similar hydrodynamics scalings is that the kurtosis, of the small-scale magnetic field increments, will increase with increasing Re. Simple theoretical arguments as well as Voyager observations indicate that effective interplanetary turbulence Re decreases with increasing heliocentric distance. The decrease of scale-dependent magnetic increment kurtosis with increasing heliocentric distance is verified using a newly refined Voyager magnetic field data set. We argue that these scalings continue to much smaller heliocentric distances approaching the Alfvén critical region, motivating a prediction that the Parker Solar Probe spacecraft will observe increased magnetic field intermittency, stronger current sheets, and more localized dissipation, as its perihelion approaches the critical regions. Similar arguments should be applicable to turbulence in other expanding astrophysical plasmas.

Keywords: Space plasmas, Heliosphere, Interplanetary turbulence, Solar wind, Plasma astrophysics