Sazuna/UAT_keywords huggingface dataset:
Recurrent Two-sided Loop Jets Caused By Magnetic Reconnection between Erupting Minifilaments and a nearby Large Filament. Using high spatial and temporal data from the New Vacuum Solar Telescope and the Solar Dynamics Observatory, we present unambiguous observations of recurrent two-sided loop jets caused by magnetic reconnection between erupting minifilaments and a nearby large filament. The observations demonstrate that three two-sided loop jets, which ejected along the large filament in opposite directions, were similar in appearance and originated from the same region. We find that a minifilament erupted and drove the first jet. It reformed at the same neutral line later, and then underwent partial and total eruptions, driving the second and third jets, respectively. In the course of the jets, cool plasma was injected into the large filament. Furthermore, persistent magnetic flux cancellation occurred at the neutral line under the minifilament before its eruption and continued until the end of the observation. We infer that magnetic flux cancellation may account for building and then triggering the minifilament to erupt to produce the two-sided loop jets. This observation not only indicates that two-sided loop jets can be driven by minifilament eruptions, but also sheds new light on our understanding of the recurrent mechanism of two-sided loop jets.

Keywords: Solar activity, Solar filaments, Solar magnetic fields
Transition Region Loops in the Very Late Phase of Flux Emergence in IRIS Sit-and-stare Observations. Loops are one of the fundamental structures that trace the geometry of the magnetic field in the solar atmosphere. Their evolution and dynamics provide a crucial proxy for studying how the magnetized structures are formed and heated in the solar atmosphere. Here, we report on spectroscopic observations of a set of transition-region loops taken by the Interface Region Imaging Spectrograph (IRIS) at Si IV 1394 Å in the sit-and-stare mode. The loops are corresponding to the flux emergence at its very late phase when the emerged magnetic features in the photosphere have fully developed. We find the transition-region loops are still expanding and moving upward with a velocity of a few kilometers per second (≲10 km s-1) at this stage. The expansion of the loops leads to interactions between the loops themselves and with the ambient field, which can drive magnetic reconnection evidenced by multiple intense brightenings, including transition-region explosive events and IRIS bombs in the footpoint region associated with the moving polarity. A set of quasi-periodic brightenings with a period of about 130 s is found at the loop apex, from which the Si IV 1394 Å profiles are significantly non-Gaussian with enhancements at both blue and red wings at Doppler velocities of about 50 km s-1. We suggest that the transition-region loops in the very late phase of flux emergence can be powered by heating events generated by the interactions between the expanding loops and the ambient fields and also by (quasi-)periodic processes, such as oscillation-modulated braiding reconnection.

Keywords: Solar atmosphere, Emerging flux tubes, Solar magnetic fields, Spectroscopy, Solar transition region
From Sun to Interplanetary Space: What is the Pathlength of Solar Energetic Particles?. Solar energetic particles (SEPs), accelerated during solar eruptions, propagate in turbulent solar wind before being observed with in situ instruments. In order to interpret their origin through comparison with remote sensing observations of the solar eruption, we thus must deconvolve the transport effects due to the turbulent magnetic fields from the SEP observations. Recent research suggests that the SEP propagation is guided by the turbulent meandering of the magnetic fieldlines across the mean magnetic field. However, the lengthening of the distance the SEPs travel, due to the fieldline meandering, has so far not been included in SEP event analysis. This omission can cause significant errors in estimation of the release times of SEPs at the Sun. We investigate the distance traveled by the SEPs by considering them to propagate along fieldlines that meander around closed magnetic islands that are inherent in turbulent plasma. We introduce a fieldline random walk model which takes into account the physical scales associated to the magnetic islands. Our method remedies the problem of the diffusion equation resulting in unrealistically short pathlengths, and the fractal dependence of the pathlength of random walk on the length of the random-walk step. We find that the pathlength from the Sun to 1 au can be below the nominal Parker spiral length for SEP events taking place at solar longitudes 45E to 60W, whereas the western and behind-the-limb particles can experience pathlengths longer than 2 au due to fieldline meandering.

Keywords: Solar energetic particles, Interplanetary turbulence, Interplanetary physics, Heliosphere
Angular Scattering in Charge Exchange: Issues and Implications for Secondary Interstellar Hydrogen. Interstellar neutral atoms provide a remote diagnostic of plasma in the outer heliosheath and the very local interstellar medium via charge exchange collisions that convert ions into atoms and vice versa. So far, most studies of interstellar atoms assumed that daughter hydrogen atoms directly inherit the kinetic properties of parent protons. This assumption neglects angular scattering of the interacting particles. However, for low relative velocities, as expected for charge exchanges in the outer heliosheath, this scattering is significant. In this study, we present how the parameters of daughter populations depend on the relative velocity and temperatures of parent populations. For this purpose, we numerically compute collision terms with and without this scattering. We find that the secondary population of interstellar hydrogen atoms, for the parent populations with the relative bulk velocity of 20 km s-1 and equal temperatures of 7500 K, has ∼2 km s-1 higher bulk velocity if the scattering is taken into account. Additionally, temperatures are higher by ∼2400 K and ∼1200 K in parallel and perpendicular directions to the relative motion of parent populations, respectively. Moreover, a significant departure of secondary atoms from the Maxwell-Boltzmann distribution is expected for high relative velocities of parent populations. This process affects the distribution and density of interstellar atoms in the heliosphere and production of pickup ions. Thus, we show that angular scattering in charge exchange collisions is important to include in analyses of interstellar neutral atoms and pickup ions observed at 1 au and in the outer heliosphere.

Keywords: Heliosphere, Interstellar atomic gas, Stellar wind bubbles, Collision physics, Interstellar medium, Charge exchange ionization, Charge exchange recombination
The 3D Structure of CO Depletion in High-mass Prestellar Regions. Disentangling the different stages of the star formation process, in particular in the high-mass regime, is a challenge in astrophysics. Chemical clocks could help alleviate this problem, but their evolution strongly depends on many parameters, leading to degeneracy in the interpretation of the observational data. One of these uncertainties is the degree of CO depletion. We present here the first self-consistent magneto-hydrodynamic simulations of high-mass, star-forming regions at different scales, fully coupled with a nonequilibrium chemical network, which includes C-N-O bearing molecules. Depletion and desorption processes are treated time dependently. The results show that full CO depletion (i.e., all gas-phase CO frozen-out on the surface of dust grains) can be reached very quickly, in one-third or even smaller fractions of the freefall time, whether the collapse proceeds on slow or fast timescales. This leads to a high level of deuteration in a short time, both for typical tracers like N2H+, as well as for the main ion {{{H}}}3+, the latter being in general larger and more extended. N2 depletion is slightly less efficient, and no direct effects on N-bearing molecules and deuterium fractionation are observed. We show that CO depletion is not the only driver of deuteration, and that there is a strong impact on D frac when changing the grain size. We finally apply a two-dimensional Gaussian point-spread function to our results to mimic observations with single-dish and interferometers. Our findings suggest that the low-values observed in high-mass star-forming clumps are in reality masking a full-depletion stage in the inner 0.1 pc region.

Keywords: Magnetohydrodynamics, Star forming regions, Massive stars, Chemical abundances, Astrochemistry, Star formation, Magnetohydrodynamical simulations
Solar Cycle Variation of Coronal Temperature, Emission Measure, and Soft X-Ray Irradiance Observed with Yohkoh Soft X-Ray Telescope. This paper presents the solar soft X-ray irradiance (0.3-3.0 nm) obtained from the mission-long full-Sun X-ray images observed with the Soft X-ray Telescope (SXT) of the Yohkoh mission (1991-2001). The irradiance was calculated using filter-ratio temperatures and emission measures (EMs) from the full-Sun integrated X-ray signals employing a coronal spectrum synthesized with CHIANTI atomic database version 8.0. Dependence of the results on the assumption of elemental abundances is investigated. The SXT irradiance for a shorter wavelength range was also calculated and compared with the low energy flux (0.1-0.8 nm) of the X-Ray Sensor on board the GOES satellite. To incorporate the spatial information of the observed corona, we tried the alternative method to derive irradiance by applying the filter-ratio method to the images of northern hemispheric corona instead of spatially integrated signals from there. The EM weighted average of the spatially resolved temperatures turned out to be generally 20%-30% lower than those derived from the integrated signals, while the total of spatially resolved EMs are accordingly 1.5-2 times higher. This trend is enhanced when solar activity is the lowest in early 1996. The irradiance obtained from the alternative method does not significantly vary from the result from the integrated signals. This provides some validation for the simpler full-Sun integrated method. The temporal variation of the EMs of cool (&lt;1.5 MK), medium, and hot (&gt;2.5 MK) components indicates that the ratio of the hot component relative to the medium component is higher in the ascending phase (mid 1998-2001) than in the descending phase (1992-1995) of the solar activity cycle.

Keywords: Solar spectral irradiance, Solar corona, Solar x-ray emission
Importance of Giant Impact Ejecta for Orbits of Planets Formed during the Giant Impact Era. Terrestrial planets are believed to be formed via giant impacts of Mars-sized protoplanets. Planets formed via giant impacts have highly eccentric orbits. A swarm of planetesimals around the planets may lead to eccentricity damping for the planets via the equipartition of random energies (dynamical friction). However, dynamical friction increases eccentricities of planetesimals, resulting in high velocity collisions between planetesimals. The collisional cascade grinds planetesimals to dust until dust grains are blown out due to radiation pressure. Therefore, the total mass of planetesimals decreases due to collisional fragmentation, which weakens dynamical friction. We investigate the orbital evolution of protoplanets in a planetesimal disk, taking into account collisional fragmentation of planetesimals. For 100 km sized or smaller planetesimals, dynamical friction is insignificant for eccentricity damping of planets because of collisional fragmentation. On the other hand, giant impacts eject collisional fragments. Although the total mass of giant impact ejecta is 0.1-0.3 Earth masses, the largest impact ejecta are ∼1000 km in size. We also investigate the orbital evolution of single planets with initial eccentricities of 0.1 in a swarm of such giant impact ejecta. Although the total mass of giant impact ejecta decreases by a factor of 3 in 30 Myr, eccentricities of planets are damped down to the Earth level (∼0.01) due to interaction with giant impact ejecta. Therefore, giant impact ejecta play an important role for determination of terrestrial planet orbits.

Keywords: Solar system formation, Solar system terrestrial planets, Planet formation
Black Hole Spin Measurement Based on Time-domain VLBI Observations of Infalling Gas Clouds. The black hole spacetime is described by general relativity and characterized by two quantities: the black hole mass and spin. Black hole spin measurement requires information from the vicinity of the event horizon, which is spatially resolved for the Galactic center Sagittarius A* (Sgr A*) and the nearby radio galaxy M87 by means of very long baseline interferometry observations with the Event Horizon Telescope (EHT). In this paper, we simulate EHT observations for a gas cloud intermittently falling onto a black hole and construct a method for spin measurement based on its relativistic flux variation. The light curve of the infalling gas cloud is composed of peaks formed by photons which directly reach a distant observer and by secondary ones reaching the observer after more than one rotation around the black hole. The time interval between the peaks is determined by a period of photon rotation near the photon circular orbit which uniquely depends on the spin. We perform synthetic EHT observations for Sgr A* under the more realistic situation where a number of gas clouds intermittently fall toward the black hole with various initial parameters. Even for this case, the black hole spin dependence is detectable in correlated flux densities which are accurately calibrated by baselines between sites with redundant stations. The synthetic observations indicate that our methodology can be applied to EHT observations of Sgr A* from 2017 April.

Keywords: Accretion, Black hole physics, Relativistic stars, Gravitation, Radiative transfer
Modeling the Thermal Bulge of a Hot Jupiter with the Two-stream Approximation. We revisit the problem of the thermal bulge of asynchronous hot Jupiters using HD 209458 b as a fiducial study. We improve upon previous works by using a double-gray atmosphere model and interior structure from MESA as the background state and then solve for the thermal bulge in response to the semidiurnal component of stellar insolation. The atmosphere model is based on the radiative transfer with Eddington’s two-stream approximation. Two opacity cases are considered: the first introduces a greenhouse effect, and the second exhibits a strong temperature inversion. We find that for the predominant thermal bulges excited by g-modes of lower orders, our results are qualitatively similar to the adiabatic results from Arras &amp; Socrates. It arises because the perturbed heating due to self-absorption of thermal emissions can be significant (i.e., greenhouse effect) against Newtonian damping, thereby leading to almost undamped thermal bulges. We also find that the contribution to the thermal bulge from the evanescent waves in the convective zone is not negligible, implying that the thermal bulge is not merely confined in the atmosphere and radiative envelope. Assuming the torque balance between the thermal and gravitational bulges, we estimate the tidal quality factor of the planet for gravitational tides to match the observed radius. The limitations of our model are also briefly discussed.

Keywords: Internal waves, Exoplanets, Hot Jupiters, Astrophysical fluid dynamics, Planetary atmospheres, Atmospheric tides, Radiative transfer equation, Tides, Planetary interior
ROME (Radio Observations of Magnetized Exoplanets). II. HD 189733 Does Not Accrete Significant Material from Its Exoplanet Like a T Tauri Star from a Disk. It has been asserted that the primary star in the HD 189733 system steadily accretes evaporated exospheric gases from its “hot Jupiter” companion, rather like a T Tauri star accreting from a disk. We conduct statistical and periodogram analyses of the photometric time series of the primary, as acquired by the automated photoelectric telescope, Microvariability and Oscillations of Stars, and Wise Observatory, to investigate this claim with the goal of revealing the presence of accretion shocks or photospheric accretion hotspots as are found in T Tauri systems such as AA Tau. None of the anticipated features were found. We re-analyze existing radio, optical, ultraviolet, and X-ray data within the framework of accreting T Tauri systems to determine physical quantities such as plasma density and temperature, accretion rate, and flare lengths. We find that with an accretion rate of \dot{M}∼ {10}9-1011 g s-1, the star is more similar to a system that intermittently absorbs gas from sungrazing comets in outburst than classical T Tauri systems, which have accretion rates at least two orders of magnitude larger. If such accretion exists, it would result in undetectably low activity at all wavelengths. Alternatively, all of the emission properties observed thus far are in agreement with stellar activity from a magnetically active star.

Keywords: Magnetohydrodynamics, Hot Jupiters, Solar-planetary interactions, Stellar activity, T Tauri stars
Various Size-sorting Processes for Millimeter-sized Particles in the Sun’s Protoplanetary Disk? Evidence from Chondrules in Ordinary Chondrites. Chondrules are approximately millimeter-sized beads of crystallized silicate melt. They formed mainly in the first ∼3 Ma of the Sun’s protoplanetary disk and are the main constituents of chondritic asteroids. Here we report on the size-frequency distributions (2D and 3D) of chondrules in the brecciated ordinary chondrite (OC) Northwest Africa (NWA) 5205. We investigated three large (centimeter- to decimeter-sized) chondritic lithic clasts of a particular textural type (“cluster chondrite”) with eye-catching different chondrule sizes. One clast shows the largest mean chondrule size (∼1.5 mm) ever measured in a chondrite. As in the other OCs, we find a positive correlation between the minimum and mean chondrule size, which we consider as an argument for chondrule size sorting. Chondrule size-frequency distributions in the clasts are distinctly more symmetric than the about log-normal distributions in other OCs. Furthermore, we find a co-enrichment of chondrule types with a priori small mean sizes (type I, porphyritic) in clasts with overall small mean chondrule sizes. We consider this as the fingerprint of an additional/second size-sorting process, which acted later on these chondrule populations. This process possibly subdivided a typical LL-type chondrule population into several subpopulations with different mean chondrule sizes. We speculate that this second sorting occurred in a unidirectional gas stream or headwind, e.g., by settling of chondrules through an asteroidal atmosphere or interaction with an expanding impact plume. Possibly, fine-grained matrix was almost completely removed by this, and the size-sorted chondrule subpopulations accreted in a hot state separately in different regions of the asteroid.

Keywords: Accretion, Chondrites, Asteroids, Chondrules, Protoplanetary disks
Sulfate Aerosol Hazes and SO<SUB>2</SUB> Gas as Constraints on Rocky Exoplanets’ Surface Liquid Water. Despite surface liquid water’s importance to habitability, observationally diagnosing its presence or absence on exoplanets is still an open problem. Inspired within the solar system by the differing sulfur cycles on Venus and Earth, we investigate thick sulfate (H2SO4-H2O) aerosol haze and high trace mixing ratios of SO2 gas as observable atmospheric features whose sustained existence is linked to the near absence of surface liquid water. We examine the fundamentals of the sulfur cycle on a rocky planet with an ocean and an atmosphere in which the dominant forms of sulfur are SO2 gas and H2SO4-H2O aerosols (as on Earth and Venus). We build a simple but robust model of the wet, oxidized sulfur cycle to determine the critical amounts of sulfur in the atmosphere-ocean system required for detectable levels of SO2 and a detectable haze layer. We demonstrate that for physically realistic ocean pH values (pH ≳ 6) and conservative assumptions on volcanic outgassing, chemistry, and aerosol microphysics, surface liquid water reservoirs with greater than 10-3 Earth oceans are incompatible with a sustained observable H2SO4-H2O haze layer and sustained observable levels of SO2. Thus, we propose the observational detection of an H2SO4-H2O haze layer and of SO2 gas as two new remote indicators that a planet does not host significant surface liquid water.

Keywords: Habitable planets, Exoplanet surface characteristics, Exoplanet atmospheres
The Formation and Evolution of Wide-orbit Stellar Multiples In Magnetized Clouds. Stars rarely form in isolation. Nearly half of the stars in the Milky Way have a companion, and this fraction increases in star-forming regions. However, why some dense cores and filaments form bound pairs while others form single stars remains unclear. We present a set of three-dimensional, gravo-magnetohydrodynamic simulations of turbulent star-forming clouds, aimed at understanding the formation and evolution of multiple-star systems formed through large-scale (≳103 au) turbulent fragmentation. We investigate three global magnetic field strengths, with global mass-to-flux ratios of μ  ϕ  = 2, 8, and 32. The initial separations of protostars in multiples depend on the global magnetic field strength, with stronger magnetic fields (e.g., μ  ϕ  = 2) suppressing fragmentation on smaller scales. The overall multiplicity fraction (MF) is between 0.4 and 0.6 for our strong and intermediate magnetic field strengths, which is in agreement with observations. The weak field case has a lower fraction. The MF is relatively constant throughout the simulations, even though stellar densities increase as collapse continues. While the MF rarely exceeds 60% in all three simulations, over 80% of all protostars are part of a binary system at some point. We additionally find that the distribution of binary spin misalignment angles is consistent with a randomized distribution. In all three simulations, several binaries originate with wide separations and dynamically evolve to ≲102 au separations. We show that a simple model of mass accretion and dynamical friction with the gas can explain this orbital evolution.

Keywords: Magnetohydrodynamics, Multiple stars, Stellar dynamics, Star formation, Interstellar clouds, Interstellar medium, Protostars, Astrophysical fluid dynamics
On the Expansion, Age, and Origin of the Puzzling Shell/Pulsar-wind Nebula G310.6-1.6. We present a 142 ks Chandra observation of the enigmatic combination supernova remnant G310.6-1.6 consisting of a bright pulsar-wind nebula driven by an energetic pulsar, surrounded by a highly circular, very faint shell with a featureless, probably synchrotron, spectrum. Comparison with an observation 6 yr earlier shows no measurable expansion of the shell, though some features in the pulsar-wind nebula have moved. We find an expansion age of at least 2500 yr, implying a current shock velocity less than about 1000 km s-1. We place severe upper limits on thermal emission from the shell; if the shell locates the blast wave, a Sedov interpretation would require the remnant to be very young, about 1000 yr, and to have resulted from a dramatically sub-energetic supernova, ejecting ≪0.02M ⊙ with energy E ≲ 3 × 1047 erg. Even a merger-induced collapse of a white dwarf to a neutron star, with a low-energy explosion, is unlikely to produce such an event. Other explanations seem equally unlikely.

Keywords: Pulsars, Supernova remnants, Astrophysical processes, Interstellar medium, Shocks