Sazuna/UAT_keywords huggingface dataset:
Interferometric Closure Phase Uncertainties in the Low Signal-to-noise Ratio Regime. Closure phases are critical in astronomical interferometry. However, their uncertainties are difficult to compute numerically. We provide a method to efficiently compute interferometric closure phase distributions in terms of an approximate distribution that is valid in the low signal-to-noise ratio regime. This is done by first showing that the true phase distribution is well approximated by the von Mises distribution, then performing a convolution of three von Mises distributions. The resulting approximation superior to the normal distribution for all signal-to-noise ratios and, being fully analytic, allows for fast computations in statistical algorithms.

Keywords: Interferometers, Astrostatistics, Astronomical instrumentation
Influence of the Interplanetary Magnetic Field Cone Angle on the Geometry of Bow Shocks. The frozen-in interplanetary magnetic field (IMF) in the solar wind is one of the most important parameters affecting the Earth's space weather. In the early studies of the IMF's influence on space weather, significant effects of the north-south component of the IMF BZ were emphasized, while the radial component of the IMF BX was largely ignored. However, the IMF near the Earth is not always dominated by the north-south component of the IMF BZ, and the radial component of the IMF BX also plays an important role. However, while the effects of the IMF BX (cone angle) on the magnetopause have been studied in recent years, there has been much less effort to quantify the BX (cone angle) effects on the bow shock. In this paper, using the bow shock crossing data from multiple satellites, we investigate the IMF cone angle effect on the dayside and nightside of the bow shock. Our results show that under the radial IMF condition, the dayside of the bow shock is located closer to the Earth than the average. At the same time, on the nightside, the bow shock is farther away from the Earth than the average. The mechanism explaining the bow shock location under the radial IMF is not completely understood. We believe that the magnetosonic Mach number and unusual conditions of the magnetosheath, especially for low dynamic pressure, play an important role. In the future, more work is needed to describe the reactions of the Earth's magnetosphere to different IMF orientations, especially to the radial IMF.

Keywords: Planetary magnetospheres, Planetary bow shocks, Interplanetary magnetic fields
The Extended Kardashev Scale. A scale is described for classifying civilizations according to the amount of power they produce, using the whole numbers 0 through 4 to denote 106, 1016, 1026, 1036, and 1046 W corresponding to the approximate power available at physical scales biological, planetary, stellar, Galactic, and observable universe, extending a Roman numeral scheme introduced by Kardashev and updating it with suggestions from Sagan and Lemarchand including using Arabic numbers to permit decimal subdivisions. Terrestrial civilization circa 2015 would be classified as Type 0.72 on this extended and updated scale. Similar scales can be used to classify information stored, population, and mass of constructions.

Keywords: Search for extraterrestrial intelligence, Astrobiology
ALMA 0.88 mm Survey of Disks around Planetary-mass Companions. Characterizing the physical properties and compositions of circumplanetary disks can provide important insights into the formation of giant planets and satellites. We report Atacama Large Millimeter/submillimeter Array 0.88 mm (Band 7) continuum observations of six planetary-mass (10-20 MJup) companions: CT Cha b, 1RXS 1609 b, ROXs 12 b, ROXs 42B b, DH Tau b, and FU Tau b. No continuum sources are detected at the locations of the companions down to 3σ limits of 120-210 μJy. Given these nondetections, it is not clear whether disks around planetary-mass companions indeed follow the disk-flux-host-mass trend in the stellar regime. The faint radio brightness of these companion disks may result from a combination of fast radial drift and a lack of dust traps. Alternatively, as disks in binary systems are known to have significantly lower millimeter fluxes due to tidal interactions, these companion disks may instead follow the relationship of moderate-separation binary stars. This scenario can be tested with sensitive continuum imaging at rms levels of ≲10 μJy.

Keywords: Radio interferometry, Extrasolar gaseous giant planets, Protoplanetary disks, Circumstellar disks
A Single-chord Stellar Occultation by the Extreme Trans-Neptunian Object (541132) Leleākūhonua. A stellar occultation by the extreme large-perihelion trans-Neptunian object (541132) Leleākūhonua (also known by the provisional designation of 2015 TG387) was predicted by the Lucky Star project and observed with the Research and Education Collaborative Occultation Network on 2018 October 20 UT. A single detection and a nearby nondetection provide constraints for the size and albedo. When a circular profile is assumed, the radius is $r={110}_{-10}^{+14} km, corresponding to a geometric albedo ${p}_{V}={0.21}_{-0.05}^{+0.03}, for an adopted absolute magnitude of HV = 5.6, typical of other objects in dynamically similar orbits. The occultation also provides a high-precision astrometric constraint.

Keywords: Detached objects, Stellar occultation, Astrometry, Trans-Neptunian objects
Lithium in T Coronae Borealis. T Coronae Borealis is a recurrent, symbiotic nova system currently in quiescence between its periodic ≈80 yr cycle of eruptions. Observations during inter-outburst epochs provide an opportunity to study properties of the accretion disk and the M red giant. Here we present new irradiated (blackbody veiling) models, incorporating modern molecular opacities and line lists, of spectra derived from high-resolution (22,000 ≲ R ≲ 120,000) optical echelle observations obtained at two epochs, one prior to and one post the 2015 rebrightening event at similar spectroscopic system phase. We find a lithium abundance in the secondary at both epochs to be comparable. The non-irradiated (classical) model atmospheres yield a lithium abundance, A(Li) = 1.3 ± 0.1. The irradiated model (veiled) atmospheres, which are likely a better representation of the system in which the white dwarf and accretion disk illuminate the red giant, give A(Li) = 2.4 ± 0.1.

Keywords: High resolution spectroscopy, Chemical abundances, Astrochemistry, Novae, Recurrent novae
H- and Dissociation in Ultra-hot Jupiters: A Retrieval Case Study of WASP-18b. Atmospheres of a number of ultra-hot Jupiters (UHJs) with temperatures ≳2000 K have been observed recently. Many of these planets show largely featureless thermal spectra in the near-infrared observed with the HST WFC3 spectrograph (1.1-1.7 μm) even though this spectral range contains strong H2O opacity. Recent works have proposed the possibility of H- opacity masking the H2O feature and/or thermal dissociation of H2O causing its apparent depletion at the high temperatures of UHJs. In this work, we test these hypotheses using observations of the exoplanet WASP-18b as a case study. We report detailed atmospheric retrievals of the planet using the HyDRA retrieval code, extended to include the effects of H- opacity and thermal dissociation. We report constraints on the H2O, CO, and H- abundances as well as the pressure-temperature profile of the dayside atmosphere for retrievals with and without H-/dissociation for each data set. We find that the H2O and H- abundances are relatively unconstrained given the featureless WFC3 spectra. We do not conclusively detect H- in the planet, contrary to previous studies that used equilibrium models to infer its presence. The constraint on the CO abundance depends on the combination of WFC3 and Spitzer data, ranging from solar to super-solar CO values. We additionally see signs of a thermal inversion from two of the data sets. Our study demonstrates the potential of atmospheric retrievals of UHJs, including the effects of H- and thermal dissociation of molecules.

Keywords: Hot Jupiters, Exoplanets, Radiative transfer, Spectroscopy, Exoplanet atmospheres
Observations of Binary Stars with the Differential Speckle Survey Instrument. IX. Observations of Known and Suspected Binaries, and a Partial Survey of Be Stars. We report 370 measures of 170 components of binary and multiple-star systems, obtained from speckle imaging observations made with the Differential Speckle Survey Instrument at Lowell Observatory's Discovery Channel Telescope in 2015 through 2017. Of the systems studied, 147 are binary stars, 10 are seen as triple systems, and 1 quadruple system is measured. Seventy-six high-quality nondetections and 15 newly resolved components are presented in our observations. The uncertainty in relative astrometry appears to be similar to our previous work at Lowell, namely, linear measurement uncertainties of approximately 2 mas, and the relative photometry appears to be uncertain at the 0.1-0.15 mag level. Using these measures and those in the literature, we calculate six new visual orbits, including one for the Be star 66 Oph and two combined spectroscopic-visual orbits. The latter two orbits, which are for HD 22451 (YSC 127) and HD 185501 (YSC 135), yield individual masses of the components at the level of 2% or better, and independent distance measures that in one case agrees with the value found in the Gaia DR2 and in the other disagrees at the 2σ level. We find that HD 22451 consists of an F6V+F7V pair with orbital period of 2401.1 ± 3.2 days and masses of 1.342 ± 0.029 and $1.236\pm 0.026\,{M}_{\odot } . For HD 185501, both stars are G5 dwarfs that orbit one another with a period of 433.94 ± 0.15 days, and the masses are 0.898 ± 0.012 and $0.876\pm 0.012\,{M}_{\odot } . We discuss the details of both the new discoveries and the orbit objects.

Keywords: Spectroscopic binary stars, Astronomical techniques, Be stars, Interferometric binary stars, Visual binary stars
Optical to Near-infrared Transmission Spectrum of the Warm Sub-Saturn HAT-P-12b. We present the transmission spectrum of HAT-P-12b through a joint analysis of data obtained from the Hubble Space Telescope Space Telescope Imaging Spectrograph and Wide Field Camera 3 and Spitzer, covering the wavelength range 0.3-5.0 μm. We detect a muted water vapor absorption feature at 1.4 μm attenuated by clouds, as well as a Rayleigh scattering slope in the optical indicative of small particles. We interpret the transmission spectrum using both the state-of-the-art atmospheric retrieval code SCARLET and the aerosol microphysics model CARMA. These models indicate that the atmosphere of HAT-P-12b is consistent with a broad range of metallicities between several tens to a few hundred times solar, a roughly solar C/O ratio, and moderately efficient vertical mixing. Cloud models that include condensate clouds do not readily generate the submicron particles necessary to reproduce the observed Rayleigh scattering slope, while models that incorporate photochemical hazes composed of soot or tholins are able to match the full transmission spectrum. From a complementary analysis of secondary eclipses by Spitzer, we obtain measured depths of 0.042% ± 0.013% and 0.045% ± 0.018% at 3.6 and 4.5 μm, respectively, which are consistent with a blackbody temperature of 890+60-70 K and indicate efficient day-night heat recirculation. HAT-P-12b joins the growing number of well-characterized warm planets that underscore the importance of clouds and hazes in our understanding of exoplanet atmospheres.

Keywords: Exoplanet astronomy, Exoplanet atmospheres
Astrophysical Insights into Radial Velocity Jitter from an Analysis of 600 Planet-search Stars. Radial velocity (RV) detection of planets is hampered by astrophysical processes on the surfaces of stars that induce a stochastic signal, or "jitter," which can drown out or even mimic planetary signals. Here, we empirically and carefully measure the RV jitter of more than 600 stars from the California Planet Search sample on a star by star basis. As part of this process, we explore the activity-RV correlation of stellar cycles and include appendices listing every ostensibly companion-induced signal we removed and every activity cycle we noted. We then use precise stellar properties from Brewer et al. to separate the sample into bins of stellar mass and examine trends with activity and with evolutionary state. We find that RV jitter tracks stellar evolution and that in general, stars evolve through different stages of RV jitter: the jitter in younger stars is driven by magnetic activity, while the jitter in older stars is convectively driven and dominated by granulation and oscillations. We identify the "jitter minimum" -- where activity-driven and convectively driven jitter have similar amplitudes -- for stars between 0.7 and 1.7 M⊙ and find that more-massive stars reach this jitter minimum later in their lifetime, in the subgiant or even giant phases. Finally, we comment on how these results can inform future RV efforts, from prioritization of follow-up targets from transit surveys like TESS to target selection of future RV surveys.

Keywords: Exoplanet detection methods, Stellar phenomena, Exoplanet astronomy, Stellar astronomy, Radial velocity
Properties of F Stars with Stable Radial Velocity Timeseries: A Useful Metric for Selecting Low-jitter F Stars. In a companion paper, we have conducted an in-depth analysis of radial velocity jitter of over 600 stars, examining the astrophysical origins including stellar granulation, oscillation, and magnetic activity. In this paper, we highlight a subsample of those stars, specifically the main sequence and "retired" F stars -- which we refer to as "MSRF" stars -- that show low levels of RV jitter (&lt;10 m s-1). We describe the observational signatures of these stars that allow them to be identified in radial velocity planet programs, for instance, those performing follow-up of transiting planets discovered by TESS. We introduce a "jitter metric" that combines the two competing effects of RV jitter with age: activity and convection. Using thresholds in the jitter metric, we can select both "complete" and "pure" samples of low jitter F stars. We also provide recipes for identifying these stars using only Gaia colors and magnitudes. Finally, we describe a region in the Gaia color-magnitude diagram where low jitter F stars are most highly concentrated. By fitting a ninth-order polynomial to the Gaia main sequence, we use the height above the main sequence as a proxy for evolution, allowing for a crude selection of low jitter MSRF stars when activity measurements are otherwise unavailable.

Keywords: Exoplanet detection methods, Radial velocity
A Comparison of Properties of Quasars with and without Rapid Broad Absorption Line Variability. We investigate the correlation between rest-frame UV flux variability of broad absorption line (BAL) quasars and their variability in BAL equivalent widths (EWs) in a various timescale from &lt;10 days to a few years in the quasar rest frame. We use the data sets of BAL EWs taken by the Sloan Digital Sky Survey Reverberation Mapping project and photometric data taken by the intermediate Palomar Transient Factory in the g and R bands and the Panoramic Survey Telescope and Rapid Response System in grizy bands. Our results are summarized as follows: (1) the distributions of flux variability versus BAL variability show weak, moderate, or a strong positive correlation; (2) there is no significant difference in flux variability amplitudes between BAL quasars with significant short timescale EW variability (called class S1) and without (class S2); (3) in all timescales considered in this paper, the class S1 quasars show systematically larger BAL variability amplitudes than those of the class S2 quasars; and (4) there are possible correlations between BAL variability and physical parameters of the quasars such as black hole masses (moderate positive), Eddington ratios, and accretion disk temperature (strong negative) in the class S2 quasars. These results indicate that the BAL variability requires changing in the ionizing continuum and an ancillary mechanism such as variability in X-ray shielding gas located at the innermost region of an accretion disk.

Keywords: Radio active galactic nuclei, Time domain astronomy, Active galactic nuclei, High-luminosity active galactic nuclei
Performance Verification of the EXtreme PREcision Spectrograph. The EXtreme PREcision Spectrograph (EXPRES) is a new Doppler spectrograph designed to reach a radial-velocity measurement precision sufficient to detect Earth-like exoplanets orbiting nearby, bright stars. We report on extensive laboratory testing and on-sky observations to quantitatively assess the instrumental radial-velocity measurement precision of EXPRES, with a focused discussion of individual terms in the instrument error budget. We find that EXPRES can reach a single-measurement instrument calibration precision better than 10 cm s-1, not including photon noise from stellar observations. We also report on the performance of the various environmental, mechanical, and optical subsystems of EXPRES, assessing any contributions to radial-velocity error. For atmospheric and telescope related effects, this includes the fast tip-tilt guiding system, atmospheric dispersion compensation, and the chromatic exposure meter. For instrument calibration, this includes the laser fRequency comb (LFC), flat-field light source, CCD detector, and effects in the optical fibers. Modal noise is mitigated to a negligible level via a chaotic fiber agitator, which is especially important for wavelength calibration with the LFC. Regarding detector effects, we empirically assess the impact on the radial-velocity precision due to pixel-position nonuniformities and charge transfer inefficiency (CTI). EXPRES has begun its science survey to discover exoplanets orbiting G-dwarf and K-dwarf stars, in addition to transit spectroscopy and measurements of the Rossiter-McLaughlin effect.

Keywords: High resolution spectroscopy, Astronomical instrumentation
Updated Parameters and a New Transmission Spectrum of HD 97658b. Recent years have seen increasing interest in the characterization of sub-Neptune-sized planets because of their prevalence in the Galaxy, contrasted with their absence in our solar system. HD 97658 is one of the brightest stars hosting a planet of this kind, and we present the transmission spectrum of this planet by combining four Hubble Space Telescope transits, 12 Spitzer/IRAC transits, and eight MOST transits of this system. Our transmission spectrum has a higher signal-to-noise ratio than those from previous works, and the result suggests that the slight increase in transit depth from wavelength 1.1-1.7 μm reported in previous works on the transmission spectrum of this planet is likely systematic. Nonetheless, our atmospheric modeling results are inconclusive, as no model provides an excellent match to our data. Nonetheless, we find that atmospheres with high C/O ratios (C/O ≳ 0.8) and metallicities of ≳100× solar metallicity are favored. We combine the mid-transit times from all of the new Spitzer and MOST observations and obtain an updated orbital period of P = 9.489295 ± 0.000005, with a best-fit transit time center at T0 = 2456361.80690 ± 0.00038 (BJD). No transit timing variations are found in this system. We also present new measurements of the stellar rotation period (34 ± 2 days) and stellar activity cycle (9.6 yr) of the host star HD 97658. Finally, we calculate and rank the Transmission Spectroscopy Metric of all confirmed planets cooler than 1000 K and with sizes between 1 R⊕ and 4 R⊕. We find that at least a third of small planets cooler than 1000 K can be well characterized using James Webb Space Telescope, and of those, HD 97658b is ranked fifth, meaning that it remains a high-priority target for atmospheric characterization.

Keywords: Hubble Space Telescope, Transit photometry, Radial velocity, Exoplanet atmospheres
Observations of the Hydrogen Cyanide in Comet 46P/Wirtanen at a 3.4 mm Wavelength. We searched for rotational lines of H12C14N in comet 46P/Wirtanen, using the Purple Mountain Observatory 13.7 m radio telescope. The J = 1-0 lines of HCN (3.4 mm wavelength) were unambiguously detected in 46P during the 2018 December 14-15 period, with a beam resolution of 62"2 and a velocity resolution of ∼0.21 km s-1 per channel. The molecular production rates were computed. The mean HCN(1-0) production rate of 46P was (6.45 ± 1.31) × 1024 molec s-1 in the above two days. We found possible indications of time variation in the outgassing activity. The average HCN abundance relative to water Q[HCN]/ ${Q}_{[{{\rm{H}}}_{2}{\rm{O}}]} of 46P was (0.09 ± 0.01)%. The HCN line shapes gave primary information on the kinematics of the cometary atmosphere. The HCN linewidths provided a direct determination of the coma expansion velocity, which was about 0.5 ± 0.05 km s-1 at post-perihelion (1.056 au).

Keywords: Comets, Short period comets, Small Solar System bodies, Comae
The TESS-Keck Survey. I. A Warm Sub-Saturn-mass Planet and a Caution about Stray Light in TESS Cameras. We report the detection of a Saturn-size exoplanet orbiting HD 332231 (TOI 1456) in light curves from the Transiting Exoplanet Survey Satellite (TESS). HD 332231 -- an F8 dwarf star with a V-band magnitude of 8.56 -- was observed by TESS in Sectors 14 and 15. We detect a single-transit event in the Sector 15 presearch data conditioning (PDC) light curve. We obtain spectroscopic follow-up observations of HD 332231 with the Automated Planet Finder, Keck I, and SONG telescopes. The orbital period we infer from radial velocity (RV) observations leads to the discovery of another transit in Sector 14 that was masked by PDC due to scattered light contamination. A joint analysis of the transit and RV data confirms the planetary nature of HD 332231 b, a Saturn-size ( ${0.867}_{-0.025}^{+0.027}\ {R}_{{\rm{J}}} ), sub-Saturn-mass ( $0.244\pm 0.021\ {M}_{{\rm{J}}} ) exoplanet on a 18.71 day circular orbit. The low surface gravity of HD 332231 b and the relatively low stellar flux it receives make it a compelling target for transmission spectroscopy. Also, the stellar obliquity is likely measurable via the Rossiter-McLaughlin effect, an exciting prospect given the 0.14 au orbital separation of HD 332231 b. The spectroscopic observations do not provide substantial evidence for any additional planets in the HD 332231 system, but continued RV monitoring is needed to further characterize this system. We also predict that the frequency and duration of masked data in the PDC light curves for TESS Sectors 14-16 could hide transits of some exoplanets with orbital periods between 10.5 and 17.5 days.

Keywords: Exoplanet detection methods, Exoplanets, Exoplanet astronomy, Direct imaging, Spectroscopy, F dwarf stars, Radial velocity, Transit photometry