adsabs/SciX_UAT_keywords huggingface dataset:
Observations of Disequilibrium CO Chemistry in the Coldest Brown Dwarfs

Cold brown dwarfs are excellent analogs of widely separated, gas giant exoplanets, and provide insight into the potential atmospheric chemistry and physics we may encounter in objects to be discovered by future direct imaging surveys. We present a low-resolution, R ∼ 300, M-band spectroscopic sequence of seven brown dwarfs with effective temperatures between 750 and 250 K along with Jupiter. These spectra reveal disequilibrium abundances of carbon monoxide (CO) produced by atmospheric quenching. We use the eddy diffusion coefficient (Kzz) to estimate the strength of vertical mixing in each object. The Kzz values of cooler gaseous objects are close to their theoretical maximum, and warmer objects show weaker mixing, likely due to less efficient convective mixing in primarily radiative layers. The CO-derived Kzz values imply that disequilibrium phosphine (PH3) should be easily observable in all of the brown dwarfs, but none as yet show any evidence for PH3 absorption. We find that ammonia is relatively insensitive to atmospheric quenching at these effective temperatures. We are able to improve the fit to WISE 0855's M-band spectrum by including both CO and water clouds in the atmospheric model.

Keywords: brown dwarfs; t subdwarfs; y dwarfs; exoplanets; free floating planets; extrasolar gaseous giant planets; exoplanet atmospheres; planetary atmospheres
Solar Cycle, Seasonal, and Dust-storm-driven Variations of the Mars Upper Atmospheric State and H Escape Rate Derived from the Lyα Emission Observed by NASA's MAVEN Mission

An accurate and systematic quantification of the state variables in the Mars upper atmosphere is important for the study of Mars volatile evolution. In this study, we perform a comprehensive analysis of the Lyα limb scans observed by MAVEN during Martian years 32-35 to quantify the Mars upper atmospheric temperature, the CO2 density, the H density, and the H thermal escape rate. A previously uncharacterized feature of the proton aurora at Mars is reported, which affects the overall shape of the limb scans without introducing peak intensity structures. Our inversion results excluding such scans demonstrate an unambiguous and systematic consistency of the Mars exobase temperature (∼150-280 K) derived from the dayside Lyα emission with those derived from the CO2+ airglow emission and those from atmospheric drag measurements, resolving a long-standing discrepancy between those different estimates. The temperature is shown to be highly predictable over different solar cycles and seasons. However, the H density and escape rate can be episodically enhanced by a factor of ∼2-3, likely driven by dust storms that coincided with the enhancements. During the three Martian years, the averaged thermal escape rates between Mars solar longitude 0°-180° and 210°-330° are 0.6 × 107 cm-2 s-1 and 9.0 × 107 cm-2 s-1, respectively, a factor of 15 seasonal difference, with a factor of ∼7.5 and ∼2 due to temperature and H density variations, respectively. These temperatures and thermal escape rates derived from the thermospheric Lyα emission are generally lower than those derived from the exospheric Lyα emission in the literature, indicating the presence of a hot H population in the Mars exosphere.

Keywords: mars; atmospheric composition; aeronomy
The Twins Embedding of Type Ia Supernovae. II. Improving Cosmological Distance Estimates

We show how spectra of Type Ia supernovae (SNe Ia) at maximum light can be used to improve cosmological distance estimates. In a companion article, we used manifold learning to build a three-dimensional parameterization of the intrinsic diversity of SNe Ia at maximum light that we call the "Twins Embedding." In this article, we discuss how the Twins Embedding can be used to improve the standardization of SNe Ia. With a single spectrophotometrically calibrated spectrum near maximum light, we can standardize our sample of SNe Ia with an rms of 0.101 ± 0.007 mag, which corresponds to 0.084 ± 0.009 mag if peculiar velocity contributions are removed and to 0.073 ± 0.008 mag if a larger reference sample were obtained. Our techniques can standardize the full range of SNe Ia, including those typically labeled as peculiar and often rejected from other analyses. We find that traditional light-curve width + color standardization such as SALT2 is not sufficient. The Twins Embedding identifies a subset of SNe Ia, including, but not limited to, 91T-like SNe Ia whose SALT2 distance estimates are biased by 0.229 ± 0.045 mag. Standardization using the Twins Embedding also significantly decreases host-galaxy correlations. We recover a host mass step of 0.040 ± 0.020 mag compared to 0.092 ± 0.026 mag for SALT2 standardization on the same sample of SNe Ia. These biases in traditional standardization methods could significantly impact future cosmology analyses if not properly taken into account.

Keywords: type ia supernovae; standard candles; observational cosmology
Total Solar Irradiance Variability on the Evolutionary Timescale and its Impact on the Earth's Mean Surface Temperature

The Sun is the primary source of energy for the Earth. The small changes in total solar irradiance (TSI) can affect our climate on the longer timescale. In the evolutionary timescale, the TSI varies by a large amount and hence its influence on the Earth's mean surface temperature (Ts) also increases significantly. We develop a mass loss dependent analytical model of TSI in the evolutionary timescale and evaluated its influence on the Ts. We determined the numerical solution of TSI for the next 8.23 Gyr to be used as an input to evaluate the Ts which formulated based on a zero-dimensional energy balance model. We used the present-day albedo and bulk atmospheric emissivity of the Earth and Mars as initial and final boundary conditions, respectively. We found that the TSI increases by 10% in 1.42 Gyr, by 40% in about 3.4 Gyr, and by 120% in about 5.229 Gyr from now, while the Ts shows an insignificant change in 1.644 Gyr and increases to 298.86 K in about 3.4 Gyr. The Ts attains the peak value of 2319.2 K as the Sun evolves to the red giant and emits the enormous TSI of 7.93 × 106 W m-2 in 7.676 Gys. At this temperature Earth likely evolves to be a liquid planet. In our finding, the absorbed and emitted flux equally increases and approaches the surface flux in the main sequence, and they are nearly equal beyond the main sequence, while the flux absorbed by the cloud shows the opposite trend.

Keywords: solar evolution; planetary climates; planetary science; planetary atmospheres
Probing the Atmospheric Precipitable Water Vapor with SOFIA, Part. IV. Water Vapor Estimates from FORCAST Grism Spectra

SOFIA was an airborne observatory for far-infrared astronomy stationed at the Armstrong Flight Research Center in Palmdale, CA, USA. Although SOFIA flew at altitudes of ~41,000 ft, any far-infrared observations from within the Earth's atmosphere are nevertheless hampered by water vapor absorbing the astronomical signal. The primary atmospheric parameter governing absorption at far-infrared wavelengths is the total upward precipitable water vapor (PWV). In this paper we present a method of deriving PWV values directly from low resolution (R ~ 100-200) mid-infrared (5-40 μm) spectroscopic observations and apply it to low resolution grism spectra obtained with the FORCAST instrument on-board SOFIA. We then compare these values with those determined from the fifth European Re-analysis (ERA5) of the global atmospheric parameters provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) for the time and altitude corresponding to the SOFIA observations. In general, we find a very good correlation between the ERA5-ECMWF values and the values derived from the FORCAST grism spectra, especially for high signal-to-noise ratio data. These results indicate that ERA5-ECMWF PWV values can be used to generate the telluric corrections for FORCAST imaging data as well as grism spectra for which the PWV values cannot be determined directly. We also derive the resolving power of the various grism and slit width combinations for FORCAST. Our results will be useful for reprocessing the FORCAST data in the SOFIA archive.

Keywords: astronomy data reduction; astronomy data analysis; astronomical instrumentation; astronomical techniques; atmospheric extinction; astronomical methods
Solitons and Turbulence in Solar Wind at 1 au: Multi-satellite Data and FDTD Simulations

During 2015 January 1-31 multi-satellite data at 1 au showed the propagation of single soliton pulses, the formation of soliton trains, and their ultimate development into the turbulence in solar wind magnetic field, density, speed, temperature, and dynamic pressure. This work is motivated by a basic research question: what are the differences in the conditions for excitation of soliton pulse, soliton train, and turbulence in the solar wind? To answer this question, a convective and dispersive system is considered and simulated via the finite difference time domain (FDTD) method. It is found that when a system is initially driven by a weak shock wave only a single soliton pulse will propagate. When the convection coefficient is smaller than or equal to the dispersion coefficient and system is driven by a strong shock then soliton trains are formed. The development of turbulence occurs when the convective coefficient dominates the dispersion coefficient and the system is driven by a stronger shock. Combining the findings of FDTD simulations with the Hall magnetohydrodynamic model, it is concluded that an enhanced interplanetary magnetic field in the magnetic sheath and the declining ion density after corotation interaction region interface provide favorable conditions for the solitons formation. Contrarily, the declining magnetic field in ejecta provides pertinent conditions for the evolution of Alfvénic turbulence. Our findings are critical for understanding the wave development into turbulence in solar wind.

Keywords: solar wind; ejecta; corotating streams; shocks; solar coronal mass ejections; fast solar wind; fast fourier transform; slow solar wind; interplanetary turbulence; solar storm; interplanetary physics; alfven waves
The Discovery of the Zeeman Effect in 38 GHz Class II Methanol Masers

Magnetic fields likely play an important role in star formation, but the number of directly measured magnetic field strengths remains scarce. We observed the 38.3 and 38.5 GHz Class II methanol (CH3OH) maser lines toward the high-mass star-forming region NGC 6334 F for the Zeeman effect. The observed spectral profiles have two prominent velocity features that can be further decomposed through Gaussian component fitting. In several of these fitted Gaussian components we find significant Zeeman detections, with zB los in the range from 8 to 46 Hz. If the Zeeman splitting factor z for the 38 GHz transitions is of the order of ~1 Hz mG-1, similar to that for several other CH3OH maser lines, then magnetic fields in the regions traced by these masers would be in the range of 8-46 mG. Such magnetic field values in high-mass star-forming regions agree with those detected in the better-known 6.7 GHz Class II CH3OH maser line. Since Class II CH3OH masers are radiatively pumped close to the protostar and likely occur in the accretion disk or the interface between the disk and outflow regions, such fields likely have significant impact on the dynamics of these disks.

Keywords: interstellar magnetic fields; star forming regions; star formation; astrophysical masers; interstellar molecules; astrosphere interstellar medium interactions; high resolution spectroscopy; spectropolarimetry
KMT-2016-BLG-1836Lb: A Super-Jovian Planet from a High-cadence Microlensing Field

We report the discovery of a super-Jovian planet in the microlensing event KMT-2016-BLG-1836, which was found by the Korea Microlensing Telescope Network (KMTNet) high-cadence observations ( ${\rm{\Gamma }}\sim 4\,{\mathrm{hr}}^{-1}$ ). The planet-host mass ratio q ∼ 0.004. A Bayesian analysis indicates that the planetary system is composed of a super-Jovian ${M}_{\mathrm{planet}}={2.2}_{-1.1}^{+1.9}{M}_{{\rm{J}}}$ planet orbiting an M or K dwarf, ${M}_{\mathrm{host}}={0.49}_{-0.25}^{+0.38}{M}_{\odot }$ , at a distance of ${D}_{{\rm{L}}}={7.1}_{-2.4}^{+0.8}$ kpc. The projected planet-host separation is ${3.5}_{-0.9}^{+1.1}$ au, implying that the planet is located beyond the snow line of the host star. Future high-resolution images can potentially strongly constrain the lens brightness and thus the mass and distance of the planetary system. Without considering detailed detection efficiency, selection, or publication biases, we find a potential mass-ratio desert at -3.7 ≲ log q ≲ -3.0 for the 31 published KMTNet planets.

Keywords: gravitational microlensing exoplanet detection
Detection of Dust in High-velocity Cloud Complex C-Enriched Gas Accreting onto the Milky Way

We present the detection of dust depletion in Complex C, a massive, infalling, low-metallicity high-velocity cloud in the northern Galactic hemisphere that traces the ongoing accretion of gas onto the Milky Way. We analyze a very high signal-to-noise Hubble Space Telescope Cosmic Origins Spectrograph spectrum of active galactic nucleus (AGN) Mrk 817 formed by coadding 165 individual exposures taken under the AGN STORM 2 program, allowing us to determine dust-depletion patterns in Complex C at unprecedented precision. By fitting Voigt components to the O I, S II, N I, Si II, Fe II, and Al II absorption and applying ionization corrections from customized CLOUDY photoionization models, we find subsolar elemental abundance ratios of [Fe/S] = -0.42 ± 0.08, [Si/S] = -0.29 ± 0.05, and [Al/S] = -0.53 ± 0.08. These ratios indicate the depletion of Fe, Si, and Al into dust grains, since S is mostly undepleted. The detection of dust provides an important constraint on the origin of Complex C, as dust grains indicate the gas has been processed through galaxies, rather than being purely extragalactic. We also derive a low metallicity of Complex C of [S/H] = -0.51 ± 0.16 (≈31% solar), confirming earlier results from this sight line. We discuss origin models that could explain the presence of dust in Complex C, including Galactic fountain models, tidal stripping from the Magellanic Clouds or other satellite galaxies, and precipitation of coronal gas onto dust-bearing "seed" clouds. * Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. These observations are associated with program 16196.

Keywords: interstellar dust; ultraviolet astronomy; high-velocity clouds; chemical abundances; circumgalactic medium
Uncovering the Ghostly Remains of an Extremely Diffuse Satellite in the Remote Halo of NGC 253

We present the discovery of NGC253-SNFC-dw1, a new satellite galaxy in the remote stellar halo of the Sculptor Group spiral, NGC 253. The system was revealed using deep, resolved star photometry obtained as part of the Subaru Near-Field Cosmology Survey that uses the Hyper Suprime-Cam on the Subaru Telescope. Although rather luminous (M V = ‑11.7 ± 0.2) and massive (M * ∼ 1.25 × 107 M ⊙), the system is one of the most diffuse satellites yet known, with a half-light radius of R h = 3.37 ± 0.36 kpc and an average surface brightness of ∼30.1 mag arcmin‑2 within the R h . The color–magnitude diagram shows a dominant, old (∼10 Gyr), and metal-poor ([M/H] = ‑1.5 ± 0.1 dex) stellar population, as well as several candidate thermally pulsing asymptotic giant branch stars. The distribution of red giant branch stars is asymmetrical and displays two elongated tidal extensions pointing toward NGC 253, suggestive of a highly disrupted system being observed at apocenter. NGC253-SNFC-dw1 has a size comparable to that of the puzzling Local Group dwarfs Andromeda XIX and Antlia 2 but is 2 magnitudes brighter. While unambiguous evidence of tidal disruption in these systems has not yet been demonstrated, the morphology of NGC253-SNFC-dw1 clearly shows that this is a natural path to produce such diffuse and extended galaxies. The surprising discovery of this system in a previously well-searched region of the sky emphasizes the importance of surface-brightness limiting depth in satellite searches. *This research is based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

Keywords: stellar populations; dwarf galaxies; tidal disruption; galaxy structure; stellar photometry; star counts
Predictions of Astrometric Jitter for Sun-like Stars. III. Fast Rotators

A breakthrough in exoplanet detections is foreseen with the unprecedented astrometric measurement capabilities offered by instrumentation aboard the Gaia space observatory. Besides, astrometric discoveries of exoplanets are expected from the planned space mission, Small-JASMINE. In this setting, the present series of papers focuses on estimating the effect of the magnetic activity of G2V-type host stars on the astrometric signal. This effect interferes with the astrometric detections of Earth-mass planets. While the first two papers considered stars rotating at the solar rotation rate, this paper focuses on stars having solar effective temperature and metallicity but rotating faster than the Sun, and consequently more active. By simulating the distribution of active regions on such stars using the Flux Emergence And Transport model, we show that the contribution of magnetic activity to the astrometric measurements becomes increasingly significant with increasing rotation rates. We further show that the jitter for the most variable periodic Kepler stars is high enough to be detected by Gaia. Furthermore, due to a decrease in the facula-to-spot area ratio for more active stars, the magnetic jitter is found to be spot dominated for rapid rotators. Our simulations of the astrometric jitter have the potential to aid the interpretation of data from Gaia and upcoming space astrometry missions.

Keywords: stellar rotation; stellar activity; astrometric exoplanet detection
The Impact of Anisotropic Sky Sampling on the Hubble Constant in Numerical Relativity

We study the impact of nearby inhomogeneities on an observer's inference of the Hubble constant. Large-scale structures induce a dependence of cosmological parameters on observer position as well as an anisotropic variance of those parameters across an observer's sky. While the former has been explored quite thoroughly, the latter has not. Incomplete sampling of an anisotropic sky could introduce a bias in our cosmological inference if we assume an isotropic expansion law. In this work, we use numerical relativity simulations of large-scale structure combined with ray tracing to produce synthetic catalogs mimicking the low-redshift Pantheon supernova (SN) data set. Our data contain all general-relativistic contributions to fluctuations in the distances and redshifts along geodesics in the simulation. We use these synthetic observations to constrain H 0 for a set of randomly positioned observers. We study both the dependence on observer position as well as the impact of rotating the sample of SNe on the observer's sky. We find a 1%–2% variance in H 0 between observers when they use an isotropic sample of objects. However, we find the inferred value of H 0 can change by up to 3%–6% when observers simply rotate their Pantheon data set on the sky. While the variances we find are below the level of the "Hubble tension," our results may suggest a reduction in the significance of the tension if anisotropy of expansion can be correctly accounted for.

Keywords: cosmology; hubble constant; general relativity; geodesics; spacetime metric
Possible Evidence of p-modes in Cassini Measurements of Saturn's Gravity Field

We analyze the range-rate residual data from Cassini's gravity experiment that cannot be explained with a static, zonally symmetric gravity field. We reproduce the data using a simple forward model of gravity perturbations from normal modes. To do this, we stack data from multiple flybys to improve sensitivity. We find a partially degenerate set of normal-mode energy spectra that successfully reproduce the unknown gravity signal from Cassini's flybys. Although there is no unique solution, we find that the models most likely to fit the data are dominated by gravitational contributions from p-modes between 500 and 700 μHz. Because f-modes at lower frequencies have stronger gravity signals for a given amplitude, this result would suggest strong frequency dependence in normal-mode excitation on Saturn. We predict peak amplitudes for p-modes on the order of several kilometers, at least an order of magnitude larger than the peak amplitudes inferred by Earth-based observations of Jupiter. The large p-mode amplitudes we predict on Saturn, if they are indeed present and steady state, would imply weak damping with a lower bound of Q > 107 for these modes, consistent with theoretical predictions.

Keywords: planetary interior; helioseismology; gravitational fields
The Distribution of Pc5 Ultralow-frequency Waves at Geostationary Orbit

Using GOES magnetometer data spanning over 30 yr, we study the distribution of Pc5 ultralow-frequency waves at geosynchronous orbit. The CLEAN algorithm was applied to detect narrowband Pc5 waves. This method was first used in astronomical radio interferometry, but has since been applied to many other areas. The algorithm allows for identification of multiple individual peaks within the same power spectral density. We found close to 30,000 events in each magnetic field component in field-aligned coordinates. With some exceptions, results were in agreement with previous studies. Wave occurrence along magnetic local time (MLT) was higher in the 18–23 MLT sector. However, the largest accumulated wave amplitudes were observed on the dayside, peaking close to local noon. As expected, wave amplitudes were larger during more active solar wind conditions. For the radial and parallel components, amplitudes were maximum at the interplanetary magnetic field clock angle of ‑30° to ‑45°. The resultant database of Pc5 ultralow-frequency wave events can be used to constrain radiation belt models, while the CLEAN method provides a unique technique to automatically detect narrowband plasma waves in the magnetosphere and beyond.

Keywords: planetary magnetospheres; alfven waves; space weather; van allen radiation belts
Tidal Truncation of Circumplanetary Disks Fails above a Critical Disk Aspect Ratio

We use numerical simulations of circumplanetary disks to determine the boundary between disks that are radially truncated by the tidal potential and those where gas escapes the Hill sphere. We consider a model problem, in which a coplanar circumplanetary disk is resupplied with gas at an injection radius smaller than the Hill radius. We evolve the disk using the PHANTOM smoothed particle hydrodynamics code until a steady state is reached. We find that the most significant dependence of the truncation boundary is on the disk aspect ratio H/R. Circumplanetary disks are efficiently truncated for H/R ≲ 0.2. For H/R ≃ 0.3, up to about half of the injected mass, depending on the injection radius, flows outward through the decretion disk and escapes. As expected from analytic arguments, the conditions (H/R and Shakura-Sunyaev α) required for tidal truncation are independent of planet mass. A simulation with larger α = 0.1 shows stronger outflow than one with α = 0.01, but the dependence on transport efficiency is less important than variations of H/R. Our results suggest two distinct classes of circumplanetary disks: tidally truncated thin disks with dust-poor outer regions, and thicker actively decreting disks with enhanced dust-to-gas ratios. Applying our results to the PDS 70 c system, we predict a largely truncated circumplanetary disk, but it is possible that enough mass escapes to support an outward flow of dust that could explain the observed disk size.

Keywords: accretion; binary stars; hydrodynamics; natural satellite formation; planet formation