Sazuna/UAT_keywords huggingface dataset:
Endogenic and Exogenic Contributions to Visible-wavelength Spectra of Europa's Trailing Hemisphere. The composition of Europa's trailing hemisphere reflects the combined influences of endogenous geologic resurfacing and exogenous sulfur radiolysis. Using spatially resolved visible-wavelength spectra of Europa obtained with the Hubble Space Telescope, we map multiple spectral features across the trailing hemisphere and compare their geographies with the distributions of large-scale geology, magnetospheric bombardment, and surface color. Based on such comparisons, we interpret some aspects of our spectra as indicative of purely exogenous sulfur radiolysis products and other aspects as indicative of radiolysis products formed from a mixture of endogenous material and magnetospheric sulfur. The spatial distributions of two of the absorptions seen in our spectra—a widespread downturn toward the near-UV and a distinct feature at 530 nm—appear consistent with sulfur allotropes previously suggested from ground-based spectrophotometry. However, the geographies of two additional features—an absorption feature at 360 nm and the spectral slope at red wavelengths—are more consistent with endogenous material that has been altered by sulfur radiolysis. We suggest irradiated sulfate salts as potential candidates for this material, but we are unable to identify particular species with the available data.

Keywords: Surface composition, Galilean satellites, Solar system astronomy
Early High-contrast Imaging Results with Keck/NIRC2-PWFS: The SR 21 Disk. High-contrast imaging of exoplanets and protoplanetary disks depends on wave front sensing and correction made by adaptive optics instruments. Classically, wave front sensing has been conducted at optical wavelengths, which made high-contrast imaging of red targets such as M-type stars or extincted T Tauri stars challenging. Keck/NIRC2 has combined near-infrared (NIR) detector technology with the pyramid wave front sensor (PWFS). With this new module we observed SR 21, a young star that is brighter at NIR wavelengths than at optical wavelengths. Compared with the archival data of SR 21 taken with the optical wave front sensing we achieved ∼20% better Strehl ratio in similar natural seeing conditions. Further post-processing utilizing angular differential imaging and reference-star differential imaging confirmed the spiral feature reported by the Very Large Telescope/Spectro-Polarimetric High-contrast Exoplanet REsearch instrument polarimetric observation, which is the first detection of the SR 21 spiral in total intensity at L' band. We also compared the contrast limit of our result (10-4 at 0"4 and 2 × 10-5 at 1"0) with the archival data that were taken with optical wave front sensing and confirmed the improvement, particularly at ≤0"5. Our observation demonstrates that the NIR PWFS improves AO performance and will provide more opportunities for red targets in the future.

Keywords: Coronagraphic imaging, Protoplanetary disks
Two-epoch Orbit Estimation for Wide Binaries Resolved in Hipparcos and Gaia. The Hipparcos catalog and its Double and Multiple System Annex (DMSA) lists 4099 components with individual proper motions and coordinates on the epoch 1991.25. Many of these long-period binary stars are also present in Gaia Data Release 2 (DR2). Using the available relative positions and proper motions separated by 24.25 yr, the equations of relative orbital motion can be solved for the two epoch eccentric anomalies, orbital period, and eccentricity. This method employs elimination of the linear Thiele-Innes unknowns and nonlinear optimization of the remaining condition equations. The quality of these solutions is compromised by the insufficient condition and modest precision of the Hipparcos astrometric data, as revealed by Monte Carlo simulations with artificially perturbed data points. The presence of multiple systems and optical pairs can also perturb the results. Limited experiments with artificial data indicate that useful estimates can be obtained with a 25 yr epoch difference for wide binaries with orbital periods up to ∼500 yr. The prospects of this method dramatically improve with the proposed next-generation space astrometry missions such as Gaia-NIR and Theia, especially when additional conditions are included from astrometric or spectroscopic measurements. An ancillary catalog of cross-identification and astrometric information for 1295 double-star pairs cross-matched in Gaia DR2 and Hipparcos is also published.

Keywords: Wide binary stars, Astrometry, Binary stars, Orbit determination
An Asymmetric Eclipse Seen toward the Pre-main-sequence Binary System V928 Tau. K2 observations of the weak-lined T Tauri binary V928 Tau A and B show the detection of a single, asymmetric eclipse, which may be due to a previously unknown substellar companion eclipsing one component of the binary with an orbital period &gt;66 days. Over an interval of about 9 hr, one component of the binary dims by around 60%, returning to its normal brightness about 5 hr later. From modeling of the eclipse shape, we find evidence that the eclipsing companion may be surrounded by a disk or a vast ring system. The modeled disk has a radius of 0.9923 ± 0.0005 R*, with an inclination of 56°78 ± 0°03, a tilt of 41°22 ± 0°05, an impact parameter of -0.2506 ± 0.0002 R*, and an opacity of 1.00. The occulting disk must also move at a transverse velocity of 6.637 ± 0.002 R* day-1, which, depending on whether it orbits V928 Tau A or B, corresponds to approximately 73.53 or 69.26 km s-1. A search in ground-based archival data reveals additional dimming events, some of which suggest periodicity, but no unambiguous period associated with the eclipse observed by K2. We present a new epoch of astrometry that is used to further refine the orbit of the binary, presenting a new lower bound of 67 yr, and constraints on the possible orbital periods of the eclipsing companion. The binary is also separated by 18″ (∼2250 au) from the lower-mass CFHT-BD-Tau 7, which is likely associated with V928 Tau A and B. We also present new high-dispersion optical spectroscopy that we use to characterize the unresolved stellar binary.

Keywords: Eclipses, Substellar companion stars, Planetary rings, Pre-main sequence stars, Astrometric binary stars
A Search for Polarized Thermal Emission from Directly Imaged Exoplanets and Brown Dwarf Companions to Nearby Stars. Aerosols in the atmospheres of cloudy gas giant exoplanets and brown dwarfs scatter and polarize these objects' thermal emission. If such an object has an oblate shape or nonuniform cloud distribution, the net degree of linear polarization can show an increase ranging from several tenths of a percent to a few percent. Modern high-contrast imaging polarimeters are now poised to detect such low-polarization signals, opening up a new window into the rotational velocities and cloud properties of substellar companions to nearby stars. In this paper, we present the results of a near-IR survey searching for linearly polarized thermal emission from a sample of two planetary-mass companions and five brown dwarf companions using GPI and SPHERE-IRDIS. We probe the subpercent linear polarization regime that typifies polarized free-floating brown dwarfs and place limits on each object's degree of linear polarization. We relate our upper limits on each target's degree of linear polarization to its rotation rate, and place our results in the context of rotation rates measured using high-resolution spectroscopy.

Keywords: Exoplanet atmospheres, Brown dwarfs, Polarimetry, Exoplanets
A Closer Look at Exoplanet Occurrence Rates: Considering the Multiplicity of Stars without Detected Planets. One core goal of the Kepler mission was to determine the frequency of Earth-like planets that orbit Sun-like stars. Accurately estimating this planet occurrence rate requires both a well-vetted list of planets and a clear understanding of the stars searched for planets. Previous ground-based follow-up observations have, through a variety of methods, sought to improve our knowledge of stars that are known to host planets. Kepler targets without detected planets, however, have not been subjected to the same intensity of follow-up observations. In this paper, we constrain better the stellar multiplicity for stars around which Kepler could have theoretically detected a transiting Earth-sized planet in the habitable zone. We subsequently aim to improve estimates of the exoplanet search completeness—the fraction of exoplanets that were detected by Kepler—with our analysis. By obtaining adaptive optics observations of 71 Kepler target stars from the Shane 3 m telescope at Lick Observatory, we detected 14 candidate stellar companions within 4″ of 13 target stars. Of these 14 candidate stellar companions, we determine through multiple independent methods that 3 are likely to be bound to their corresponding target star. We then assess the impact of our observations on exoplanet occurrence rate calculations, finding an increase in occurrence of 6% (0.9σ) for various estimates of the frequency of Earth-like planets and an increase of 26% (4.5σ) for super-Earths and sub-Neptunes. These occurrence increases are not entirely commensurate with theoretical predictions, though this discrepancy may be due to differences in the treatment of stellar binarity.

Keywords: Observational astronomy, Binary stars, Exoplanet catalogs, Near infrared astronomy
Beyond Equilibrium Temperature: How the Atmosphere/Interior Connection Affects the Onset of Methane, Ammonia, and Clouds in Warm Transiting Giant Planets. The atmospheric pressure-temperature profiles for transiting giant planets cross a range of chemical transitions. Here we show that the particular shapes of these irradiated profiles for warm giant planets below ∼1300 K lead to striking differences in the behavior of nonequilibrium chemistry compared to brown dwarfs of similar temperatures. Our particular focus is H2O, CO, CH4, CO2, and NH3 in Jupiter- and Neptune-class planets. We show that the cooling history of a planet, which depends most significantly on planetary mass and age, can have a dominant effect on abundances in the visible atmosphere, often swamping trends one might expect based on Teq alone. The onset of detectable CH4 in spectra can be delayed to lower Teq for some planets compared to equilibrium, or pushed to higher Teq. The detectability of NH3 is typically enhanced compared to equilibrium expectations, which is opposite to the brown dwarf case. We find that both CH4 and NH3 can become detectable at around the same Teq (at Teq values that vary with mass and metallicity), whereas these "onset" temperatures are widely spaced for brown dwarfs. We suggest observational strategies to search for atmospheric trends and stress that nonequilibrium chemistry and clouds can serve as probes of atmospheric physics. As examples of atmospheric complexity, we assess three Neptune-class planets, GJ 436b, GJ 3470b, and WASP-107, all around Teq = 700 K. Tidal heating due to eccentricity damping in all three planets heats the deep atmosphere by thousands of degrees and may explain the absence of CH4 in these cool atmospheres. Atmospheric abundances must be interpreted in the context of physical characteristics of the planet.

Keywords: Exoplanet atmospheres
Heliospheric Structure as Revealed by the 3-88 keV H ENA Spectra. Energetic neutral atoms (ENAs) are an important tool for investigating the structure of the heliosphere. Recently, it was observed that fluxes of ENAs (with energy ≤55 keV) coming from the upwind and downwind regions of the heliosphere are similar in strength. This led the authors of these observations to hypothesize that the heliosphere is bubble-like rather than comet-like, meaning that it has no extended tail. We investigate the directional distribution of the ENA flux for a wide energy range (3-88 keV) including observations from IBEX (Interstellar Boundary Explorer), INCA (Ion and Neutral Camera, on board Cassini), and HSTOF (High-energy Suprathermal Time Of Flight sensor, on board the Solar and Heliospheric Observatory). An essential element is the model of pickup ion (PUI) acceleration at the termination shock proposed by Zank. We use state-of-the-art models of the global heliosphere, interstellar neutral gas density, and PUI distributions. The results, based on the “comet-like” model of the heliosphere, are close in flux magnitude to ENA observations by IBEX, HSTOF, and partly those by INCA (except for the 5.2-13.5 keV energy channel). We find that the ENA flux from the tail dominates at high energy (in agreement with HSTOF, but not INCA). At low energy, our comet-like model produces ENA fluxes of similar strength from the upwind and downwind directions—which, therefore, removes this as a compelling argument for a bubble-like heliosphere.

Keywords: Heliopause, Heliosphere, Solar wind, Solar wind termination, Pickup ions, Solar physics, Interplanetary particle acceleration, Interplanetary physics
Temporal Variability in Hot Jupiter Atmospheres. Hot Jupiters receive intense incident stellar light on their daysides, which drives vigorous atmospheric circulation that attempts to erase their large dayside-to-nightside flux contrasts. Propagating waves and instabilities in hot Jupiter atmospheres can cause emergent properties of the atmosphere to be time-variable. In this work, we study such weather in hot Jupiter atmospheres using idealized cloud-free general circulation models with double-gray radiative transfer. We find that hot Jupiter atmospheres can be time-variable at the ∼0.1%-1% level in globally averaged temperature and at the ∼1%-10% level in globally averaged wind speeds. As a result, we find that observable quantities are also time-variable: the secondary eclipse depth can be variable at the ≲2% level, the phase-curve amplitude can change by ≲1%, the phase-curve offset can shift by ≲5°, and terminator-averaged wind speeds can vary by ≲2 km s-1. Additionally, we calculate how the eastern and western limb-averaged wind speeds vary with incident stellar flux and the strength of an imposed drag that parameterizes Lorentz forces in partially ionized atmospheres. We find that the eastern limb is blueshifted in models over a wide range of equilibrium temperature and drag strength, while the western limb is only redshifted if equilibrium temperatures are ≲1500 K and drag is weak. Lastly, we show that temporal variability may be observationally detectable in the infrared through secondary eclipse observations with the James Webb Space Telescope, phase-curve observations with future space telescopes (e.g., ARIEL), and/or Doppler wind speed measurements with high-resolution spectrographs.

Keywords: Exoplanets, Hydrodynamics, Exoplanet atmospheric variability, Computational methods, Exoplanet atmospheres
The Multi-slit Approach to Coronal Spectroscopy with the Multi-slit Solar Explorer (MUSE). The Multi-slit Solar Explorer (MUSE) is a proposed mission aimed at understanding the physical mechanisms driving the heating of the solar corona and the eruptions that are at the foundation of space weather. MUSE contains two instruments, a multi-slit extreme ultraviolet (EUV) spectrograph and a context imager. It will simultaneously obtain EUV spectra (along 37 slits) and context images with the highest resolution in space (0.″33-0.″4) and time (1-4 s) ever achieved for the transition region (TR) and corona. The MUSE science investigation will exploit major advances in numerical modeling, and observe at the spatial and temporal scales on which competing models make testable and distinguishable predictions, thereby leading to a breakthrough in our understanding of coronal heating and the drivers of space weather. By obtaining spectra in four bright EUV lines (Fe IX 171 Å, Fe XV 284 Å, Fe XIX 108Å, Fe XXI 108 Å) covering a wide range of TR and coronal temperatures along 37 slits simultaneously, MUSE will be able to “freeze” the evolution of the dynamic coronal plasma. We describe MUSE’s multi-slit approach and show that the optimization of the design minimizes the impact of spectral lines from neighboring slits, generally allowing line parameters to be accurately determined. We also describe a Spectral Disambiguation Code to resolve multi-slit ambiguity in locations where secondary lines are bright. We use simulations of the corona and eruptions to perform validation tests and show that the multi-slit disambiguation approach allows accurate determination of MUSE observables in locations where significant multi-slit contamination occurs.

Keywords: High resolution spectroscopy, Solar extreme ultraviolet emission, Astronomy data analysis, Spectroscopy, Solar instruments
X-shooter Spectroscopy and HST Imaging of 15 Massive Quiescent Galaxies at z ≳ 2. We present a detailed analysis of a large sample of spectroscopically confirmed massive quiescent galaxies (MQGs; log(M */M ☉) ∼ 11.5) at z ≳ 2. This sample comprises 15 galaxies selected in the COSMOS and UDS fields by their bright K-band magnitudes and followed up with Very Large Telescope (VLT) X-shooter spectroscopy and Hubble Space Telescope (HST)/WFC3 H F160W imaging. These observations allow us to unambiguously confirm their redshifts, ascertain their quiescent nature and stellar ages, and reliably assess their internal kinematics and effective radii. We find that these galaxies are compact, consistent with the high-mass end of the stellar mass-size relation for quiescent galaxies at z = 2. Moreover, the distribution of the measured stellar velocity dispersions of the sample is consistent with the most massive local early-type galaxies from the MASSIVE Survey, showing that evolution in these galaxies is dominated by changes in size. The HST images reveal, as surprisingly high, that 40% of the sample has tidal features suggestive of mergers and companions in close proximity, including three galaxies experiencing ongoing major mergers. The absence of velocity dispersion evolution from z = 2 to 0, coupled with a doubling of the stellar mass, with a factor of 4 size increase and the observed disturbed stellar morphologies, supports dry minor mergers as the primary drivers of the evolution of the MQGs over the last 10 billion yr.

Keywords: High resolution spectroscopy, Quenched galaxies, Stellar ages, Compact galaxies, Hubble Space Telescope, Galaxy dynamics, Stellar radii, Infrared astronomy, Galaxy kinematics, Infrared galaxies, Stellar masses, Near infrared astronomy
In Situ Observations of Separatrices in a Strong-guide-field Reconnection at the Magnetopause. The reconnection in nearly symmetric inflow boundary conditions with a strong guide field of three is detected at the magnetopause. The thin current sheet was well resolved by the Magnetospheric Multiscale mission, which revealed that there is a pair of low-density separatrices and a pair of higher-density separatrices. Electron flow is accelerated toward the X-line along the low-density side and ejected out along the higher-density side. All flows are super-Alfvénic, but the outflow velocity is much lower than the inflow velocity. It is further shown that the width of higher-density separatrices is about twice that of the low-density separatrices. Significant and opposite electric field activity is observed on both sides of the current sheet. Our observations show that the separatrix regions between the two sides of strong-guide-field reconnection are significantly different in structure and plasma properties, which in turn affect the acceleration and heating of electrons.

Keywords: Space plasmas, Geomagnetic fields, Plasma jets, Plasma physics, Plasma astrophysics, Interplanetary particle acceleration, Magnetic fields
Evidence for a Highly Opaque Large-scale Galaxy Void at the End of Reionization. We present evidence that a region of high effective Lyα optical depth at z ∼ 5.7 is associated with an underdense region at the tail end of cosmic reionization. We carried out a survey of Lyman-break Galaxies (LBGs) using Subaru Hyper Suprime-Cam in the field of the z = 5.98 quasar J0148+0600, whose spectrum presents an unusually long (∼160 cMpc) and opaque (τ ≳ 7) Lyα trough at 5.5 ≤ z ≤ 5.9. LBG candidates were selected to lie within the redshift range of the trough, and the projected number densities were measured within 90 cMpc of the quasar sightline. The region within 8‧ (or ≈19 cMpc) of the quasar position is the most underdense of the whole field. The significance of the presence of the void is estimated to be 99%. This is consistent with the significant deficit of Lyα emitters (LAEs) at z = 5.72 reported by Becker et al. and suggests that the paucity of LAEs is not purely due to the removal of the Lyα emission by the high opacity but reflects a real coherent underdensity of galaxies across the entire redshift range of the trough. These observations are consistent with scenarios in which large optical depth fluctuations arise due to fluctuations in the galaxy-dominant UV background or due to residual neutral islands that are expected from reionization that is completed at redshifts as low as z ≲ 5.5.

Keywords: Reionization, Lyman-break galaxies, Lyman alpha forest, Intergalactic medium
Irregular Dust Features around Intermediate-mass Young Stars with GPI: Signs of Youth or Misaligned Disks?. We are undertaking a large survey of over 30 disks using the Gemini Planet Imager (GPI) to see whether the observed dust structures match spectral energy distribution predictions and have any correlation with stellar properties. GPI can observe near-infrared light scattered from dust in circumstellar environments using high-resolution Polarimetric Differential Imaging with coronagraphy and adaptive optics. The data have been taken in the J and H bands over two years, with inner working angles of 0.″08 and 0.″11, respectively. Ahead of the release of the complete survey results, here we present five objects with extended and irregular dust structures within 2″ of the central star. These objects are FU Ori, MWC 789, HD 45677, Hen 3-365, and HD 139614. The observed structures are consistent with each object being a pre-main-sequence star with protoplanetary dust. The five objects’ circumstellar environments could result from extreme youth and complex initial conditions, from asymmetric scattering patterns due to shadows cast by misaligned disks, or in some cases from interactions with companions. We see complex U  ϕ  structures in most objects that could indicate multiple scattering or result from the illumination of companions. Specific key findings include the first high-contrast observation of MWC 789 revealing a newly discovered companion candidate and arc, and two faint companion candidates around Hen 3-365. These two objects should be observed further to confirm whether the companion candidates are comoving. Further observations and modeling are required to determine the causes of the structures.

Keywords: Coronagraphic imaging, Protoplanetary disks, Circumstellar dust, Polarimetry, Near infrared astronomy
NuSTAR Discovery of a Compton-thick, Dust-obscured Galaxy: WISE J0825+3002. We report the discovery of a Compton-thick (CT), dust-obscured galaxy at z = 0.89, WISE J082501.48+300257.2 (WISE 0825+3002), observed by the Nuclear Spectroscopic Telescope Array. X-ray analysis with the XCLUMPY model revealed that hard X-ray luminosity in the rest-frame 2-10 keV band of WISE 0825+3002 is L X (2-10 keV) = {4.2}-1.6+2.8× {10}44 erg s-1 while its hydrogen column density is N H = {1.0}-0.4+0.8× {10}24 cm-2, indicating that WISE 0825+3002 is a mildly CT active galactic nucleus (AGN). We performed spectral energy distribution (SED) fitting with CIGALE to derive its stellar mass, star formation rate, and infrared luminosity. The estimated Eddington ratio based on stellar mass and integration of the best-fit SED of the AGN component is λ Edd = 0.70, which suggests that WISE 0825+3002 harbors an actively growing black hole behind a large amount of gas and dust. We found that the relationship between the luminosity ratio of X-ray and 6 μm, and Eddington ratio, follows an empirical relation for AGNs reported by Toba et al.

Keywords: Observational astronomy, Supermassive black holes, Active galactic nuclei, X-ray active galactic nuclei, Infrared galaxies