adsabs/SciX_UAT_keywords huggingface dataset:
Characterization of the Nucleus, Morphology, and Activity of Interstellar Comet 2I/Borisov by Optical and Near-infrared GROWTH, Apache Point, IRTF, ZTF, and Keck Observations

We present visible and near-infrared (NIR) photometric and spectroscopic observations of interstellar object (ISO) 2I/Borisov taken from 2019 September 10 to 2019 December 20 using the GROWTH, the Apache Point Observatory Astrophysical Research Consortium 3.5 m, and the NASA Infrared Telescope Facility 3.0 m combined with pre- and postdiscovery observations of 2I obtained by the Zwicky Transient Facility from 2019 March 17 to 2019 May 5. Comparison with imaging of distant solar system comets shows an object very similar to mildly active solar system comets with an outgassing rate of ∼1027 mol s-1. The photometry, taken in filters spanning the visible and NIR range, shows a gradual brightening trend of ∼0.03 mag day-1 since 2019 September 10 UTC for a reddish object becoming neutral in the NIR. The light curve from recent and prediscovery data reveals a brightness trend suggesting the recent onset of significant H2O sublimation with the comet being active with super volatiles such as CO at heliocentric distances >6 au consistent with its extended morphology. Using the advanced capability to significantly reduce the scattered light from the coma enabled by high-resolution NIR images from Keck adaptive optics taken on 2019 October 4, we estimate a diameter for 2I's nucleus of ≲1.4 km. We use the size estimates of 1I/'Oumuamua and 2I/Borisov to roughly estimate the slope of the ISO size distribution, resulting in a slope of ∼3.4 ± 1.2, similar to solar system comets and bodies produced from collisional equilibrium.

Keywords: comets
First Report of a Solar Energetic Particle Event Observed by China's Tianwen-1 Mission in Transit to Mars

Solar energetic particles (SEPs) associated with flares and/or coronal mass ejection (CME)-driven shocks can impose acute radiation hazards on space explorations. To measure energetic particles in near-Mars space, the Mars Energetic Particle Analyzer (MEPA) instrument on board China's Tianwen-1 (TW-1) mission was designed. Here, we report the first MEPA measurements of the widespread SEP event occurring on 2020 November 29 when TW-1 was in transit to Mars. This event occurred when TW-1 and Earth were magnetically well connected, known as the Hohmann-Parker effect, thus offering us a rare opportunity to understand the underlying particle acceleration and transport process. Measurements from TW-1 and near-Earth spacecraft show similar double-power-law spectra and a radial dependence of the SEP peak intensities. Moreover, the decay phases of the time-intensity profiles at different locations clearly show the reservoir effect. We conclude that the double-power-law spectrum is likely generated at the acceleration site and that a small but finite cross-field diffusion is crucial to understanding the formation of the SEP reservoir phenomenon. These results provide insight into particle acceleration and transport associated with CME-driven shocks, which may contribute to the improvement of relevant physical models.

Keywords: solar energetic particles
Searching the Entirety of Kepler Data. II. Occurrence Rate Estimates for FGK Stars

We present exoplanet occurrence rates estimated with approximate Bayesian computation for planets with radii between 0.5 and 16 R⊕ and orbital periods between 0.78 and 400 days orbiting FGK dwarf stars. We base our results on an independent planet catalog compiled from our search of all ∼200,000 stars observed over the Kepler mission, with precise planetary radii supplemented by Gaia DR2-incorporated stellar radii. We take into account detection and vetting efficiency, planet radius uncertainty, and reliability against transit-like noise signals in the data. By analyzing our FGK occurrence rates as well as those computed after separating F-, G-, and K-type stars, we explore dependencies on stellar effective temperature, planet radius, and orbital period. We reveal new characteristics of the photoevaporation-driven "radius gap" between ∼1.5 and 2 R⊕, indicating that the bimodal distribution previously revealed for P < 100 days exists only over a much narrower range of orbital periods, above which sub-Neptunes dominate and below which super-Earths dominate. Finally, we provide several estimates of the "eta-Earth" value—the frequency of potentially habitable, rocky planets orbiting Sun-like stars. For planets with sizes 0.75-1.5 R⊕ orbiting in a conservatively defined habitable zone (0.99-1.70 au) around G-type stars, we place an upper limit (84.1th percentile) of <0.18 planets per star.

Keywords: exoplanets; habitable planets; exoplanet catalogs; transit photometry; bayesian statistics; astrostatistics
Evidence for TiO in the Atmosphere of the Hot Jupiter HAT-P-65 b

We present the low-resolution transmission spectra of the puffy hot Jupiter HAT-P-65b (0.53 MJup, 1.89 RJup, Teq = 1930 K), based on two transits observed using the OSIRIS spectrograph on the 10.4 m Gran Telescopio CANARIAS. The transmission spectra of the two nights are consistent, covering the wavelength range 517-938 nm and consisting of mostly 5 nm spectral bins. We perform equilibrium-chemistry spectral retrieval analyses on the jointly fitted transmission spectrum and obtain an equilibrium temperature of ${1645}_{-244}^{+255}$ K and a cloud coverage of ${36}_{-17}^{+23}$ %, revealing a relatively clear planetary atmosphere. Based on free-chemistry retrieval, we report strong evidence for titanium oxide (TiO). Additional individual analyses in each night reveal weak-to-moderate evidence for TiO in both nights, but moderate evidence for Na or VO only in one of the nights. Future high-resolution Doppler spectroscopy as well as emission observations will help confirm the presence of TiO and constrain its role in shaping the vertical thermal structure of HAT-P-65b's atmosphere.

Keywords: exoplanet atmospheres; exoplanet atmospheric composition; transmission spectroscopy; hot jupiters; exoplanets
Magnetohydrodynamic Simulations of Spicular Jet Propagation Applied to Lower Solar Atmosphere Model. II. Case Studies with Tilted Jets

We report on numerical simulations of a propagating momentum pulse, representing an inclined jet structure in a stratified lower solar atmosphere model. Here, the numerical jets were generated via injection of a momentum pulse misaligned with the radial magnetic field, which resulted in a collimated structure that mimicked the observed inclined jet features in the chromosphere. The influence of inclination angle was examined for a variety of initial driver conditions (amplitude, period) and magnetic field magnitudes to identify their potential role in determining the morphological and dynamical characteristics of chromospheric jets. The numerical jets in our computational domain were consistent with the observed magnitudes of apex height and cross-sectional width for average inclination of chromospheric features. Furthermore, with an increasing misalignment between the momentum pulse and ambient magnetic field, the simulated structures showed a drop in the maximum apex height and length, while an increase in cross-sectional width magnitudes. Our numerical experiments also revealed the development of a pulse-like transverse motions in jets along with high density edges/nodes in the direction of jet displacement. It is postulated that dynamic kink instability might be responsible for the observed kinematic behavior of the inclined jet structures in the solar chromosphere.

Keywords: solar physics; the sun; solar spicules; solar chromosphere; magnetohydrodynamical simulations
Sun-as-a-star Analyses of Various Solar Active Events Using Hα Spectral Images Taken by SMART/SDDI

Sun-as-a-star analyses in which observational data is spatially integrated are useful for interpreting stellar data. For future applications to stellar observations, we performed Sun-as-a-star analyses of Hα spectra for various active events on the Sun, not only for flares and filament eruptions/surges on the solar disk, but also for eruptions of off-limb prominences using Hα spectral images taken by the Solar Magnetic Activity Research Telescope/Solar Dynamics Doppler Imager at Hida Observatory, Kyoto University. All the analyzed events show emission relative to the pre-event state and the changes in their Hα equivalent widths are all on the orders of 10-4 Å. Sun-as-a-star Hα spectra exhibit different features depending on the causes of the emission: (i) flares show emission at the Hα line center, together with red asymmetry and line broadening, as reported in a previous study, (ii) filament eruptions with and without flares show emission near the Hα line center, accompanied by blueshifted/redshifted absorption; notably, the disappearance of dark filaments leads to the apparent enhancement of the Hα line center emission, and (iii) eruptions of off-limb prominences show blueshifted/redshifted emission. These spectral features enable us to identify the active phenomena on Sun-like stars. We have also found that even the filament eruptions showing redshifted absorptions in Sun-as-a-star Hα spectra lead to coronal mass ejections (CMEs). This result suggests that even if the falling components of stellar filament eruptions are detected as redshifted absorptions in Hα spectra, such stellar filament eruptions may also develop into CMEs.

Keywords: solar flares; stellar flares; solar filament eruptions; solar prominences; solar coronal mass ejections; stellar coronal mass ejections; solar chromosphere
TOI-3757 b: A Low-density Gas Giant Orbiting a Solar-metallicity M Dwarf

We present the discovery of a new Jovian-sized planet, TOI-3757 b, the lowest-density transiting planet known to orbit an M dwarf (M0V). This planet was discovered around a solar-metallicity M dwarf, using Transiting Exoplanet Survey Satellite photometry and confirmed with precise radial velocities from the Habitable-zone Planet Finder (HPF) and NEID. With a planetary radius of 12.0 ${}_{-0.5}^{+0.4}$ R ⊕ and mass of 85.3 ${}_{-8.7}^{+8.8}$ M ⊕, not only does this object add to the small sample of gas giants (~10) around M dwarfs, but also its low density ( $\rho ={0.27}_{-0.04}^{+0.05}$ g cm-3) provides an opportunity to test theories of planet formation. We present two hypotheses to explain its low density; first, we posit that the low metallicity of its stellar host (~0.3 dex lower than the median metallicity of M dwarfs hosting gas giants) could have played a role in the delayed formation of a solid core massive enough to initiate runaway accretion. Second, using the eccentricity estimate of 0.14 ± 0.06, we determine it is also plausible for tidal heating to at least partially be responsible for inflating the radius of TOI-3757b b. The low density and large scale height of TOI-3757 b makes it an excellent target for transmission spectroscopy studies of atmospheric escape and composition (transmission spectroscopy measurement of ~ 190). We use HPF to perform transmission spectroscopy of TOI-3757 b using the helium 10830 Å line. Doing this, we place an upper limit of 6.9% (with 90% confidence) on the maximum depth of the absorption from the metastable transition of He at ~10830 Å, which can help constraint the atmospheric mass-loss rate in this energy-limited regime.

Keywords: exoplanet astronomy; hot jupiters; exoplanets; radial velocity; exoplanet detection methods; transits
Simultaneous Optical Transmission Spectroscopy of a Terrestrial, Habitable-zone Exoplanet with Two Ground-based Multiobject Spectrographs

Investigating the atmospheres of rocky exoplanets is key to performing comparative planetology between these worlds and the terrestrial planets that reside in the inner solar system. Terrestrial exoplanet atmospheres exhibit weak signals, and attempting to detect them pushes at the boundaries of what is possible for current instrumentation. We focus on the habitable-zone terrestrial exoplanet LHS 1140b. Given its 25-day orbital period and 2 hr transit duration, capturing transits of LHS 1140b is challenging. We observed two transits of this object, approximately 1 yr apart, which yielded four data sets thanks to our simultaneous use of the IMACS and LDSS3C multiobject spectrographs mounted on the twin Magellan telescopes at Las Campanas Observatory. We present a jointly fit white light curve, as well as jointly fit 20 nm wavelength-binned light curves from which we construct a transmission spectrum. Binning the joint white light-curve residuals to 3-minute time bins gives an rms of 145 ppm; binning down to 10-minute time bins gives an rms of 77 ppm. Our median uncertainty in ${R}_{p}^{2}/{R}_{s}^{2}$ in the 20 nm wavelength bins is 260 ppm, and we achieve an average precision of 1.3× the photon noise when fitting the wavelength-binned light curves with a Gaussian process regression. Our precision on ${R}_{p}^{2}/{R}_{s}^{2}$ is a factor of four larger than the feature amplitudes of a clear, hydrogen-dominated atmosphere, meaning that we are not able to test realistic models of LHS 1140b's atmosphere. The techniques and caveats presented here are applicable to the growing sample of terrestrial worlds in the Transiting Exoplanet Survey Satellite era, as well as to the upcoming generation of ground-based giant segmented mirror telescopes.

Keywords: exoplanet atmospheres; transits; spectroscopy; planetary atmospheres
The Effect of Warm Dark Matter on Early Star Formation Histories of Massive Galaxies: Predictions from the CROC Simulations

Several massive (M* > 108 M⊙), high-redshift (z = 8-10) galaxies have recently been discovered to contain stars with ages of several hundred million years, pushing the onset of star formation in these galaxies back to z ∼ 15. The very existence of stars formed so early may serve as a test for cosmological models with suppressed small-scale power (and, hence, late formation of cosmic structure). We explore the ages of the oldest stars in numerical simulations from the Cosmic Reionization On Computers project with cold dark matter (CDM) and two warm dark matter (WDM) cosmologies with 3 and 6 keV particles. There are statistically significant differences of ∼5 Myr between average stellar ages of massive galaxies in CDM and 3 keV WDM, while CDM and 6 keV WDM are statistically indistinguishable. Even this 5 Myr difference, however, is much less than current observational uncertainties on the stellar population properties of high-redshift galaxies. The age distributions of all galaxies in all cosmologies fail to produce a substantial Balmer break, although uncertainties in dust attenuation are a potentially significant factor. Finally, we assess the convergence of our simulation predictions and find that the systematic uncertainties on individual galaxy properties are comparable to the differences between cosmologies, suggesting these differences may not be numerically robust.

Keywords: cosmology; dark matter; galaxies
Predicting the Exoplanet Yield of the TESS Prime and Extended Missions through Years 1-7

The Transiting Exoplanet Survey Satellite (TESS) has discovered ~5000 planets and planet candidates after 3.5 yr. With a planned second Extended Mission (EM2) spanning Years 5-7 on the horizon, now is the time to revise predictions of the TESS exoplanet yield. We present simulations of the number of detectable planets around 9.4 million AFGKM stars in the TESS Candidate Target List v8.01 through 7 yr of observations. Our simulations take advantage of improved models for the photometric performance, temporal window functions, and transit detection probability. We estimate that 4719 ± 334 planets should be detectable with the Prime Mission alone (Years 1-2), and another 3707 ± 209 should be detectable across the current Extended Mission (Years 3-4). Based on a proposed pointing scenario for EM2, we predict that TESS should find another 4093 ± 180 planets, bringing the total TESS yield to 12,519 ± 678. We provide our predicted yields as functions of host star spectral type, planet radius, orbital period, follow-up feasibility, and location relative to the habitable zone. As TESS continues, new planets will be progressively smaller, with longer orbital periods, and will orbit fainter stars. Half of the planets found in EM2 will be smaller than 4 R ⊕, and over 1200 will have orbital periods longer than 20 days, effectively doubling the TESS yields of both kinds of planets. The number of small (<2 R ⊕) habitable-zone planets will also double, bringing the total TESS yield to 18 ± 5. We also compare our predictions to the actual Prime Mission yield, finding good agreement.

Keywords: transit photometry; exoplanets
Tidal Disruption of Planetesimals from an Eccentric Debris Disk Following a White Dwarf Natal Kick

The surfaces of many white dwarfs are polluted by metals, implying a recent accretion event. The tidal disruption of planetesimals is a viable source of white dwarf pollution and offers a unique window into the composition of exoplanet systems. The question of how planetary material enters the tidal disruption radius of the white dwarf is currently unresolved. Using a series of N-body simulations, we explore the response of the surrounding planetesimal debris disk as the white dwarf receives a natal kick caused by anisotropic mass loss on the asymptotic giant branch. We find that the kick can form an apse-aligned, eccentric debris disk in the range 30–240 au, which corresponds to the orbits of Neptune, the Kuiper Belt, and the scattered disk in our solar system. In addition, many planetesimals beyond 240 au flip to counterrotating orbits. Assuming an isotropic distribution of kicks, we predict that approximately 80% of white dwarf debris disks should exhibit significant apsidal alignment and a fraction of counterrotating orbits. The eccentric disk is able to efficiently and continuously torque planetesimals onto radial, star-grazing orbits. We show that the kick causes both an initial burst in tidal disruption events as well as an extended period of 100 Myr where tidal disruption rates are consistent with observed mass accretion rates on polluted white dwarfs.

Keywords: planetary dynamics; white dwarf stars; tidal disruption; n-body simulations
Probing the Icy Shell Structure of Ocean Worlds with Gravity-Topography Admittance

The structure of the icy shells of ocean worlds is important for understanding the stability of their underlying oceans as it controls the rate at which heat can be transported outward and radiated to space. Future spacecraft exploration of the ocean worlds (e.g., by NASA's Europa Clipper mission) will allow for higher-resolution measurements of gravity and shape than currently available. In this paper, we study the sensitivity of gravity-topography admittance to the structure of icy shells in preparation for future data analysis. An analytical viscous relaxation model is used to predict admittance spectra given different shell structures determined by the temperature-dependent viscosity of a tidally heated, conductive shell. We apply these methods to the ocean worlds of Europa and Enceladus. We find that admittance is sensitive to the mechanisms of topography support at different wavelengths and estimate the required gravity performance to resolve transitions between these mechanisms. We find that measuring admittance would be complementary to ice-penetrating radar in constraining shell thickness as it would cover the cases for which a direct ice-ocean interface detection is less favorable with radar, i.e., for warmer and thicker shells. Finally, we find that admittance may be used to constrain the tidal dissipation within the icy shell, which would be complementary to a more demanding measurement of the tidal phase lag.

Keywords: ocean planets; europa; saturnian satellites; tides
Reactive Rate Constants for the C+ + H2(v = 0, 1) Reaction: An Accurate State-to-state Quantum Dynamical Study

The accurately calculated thermal rate constants of the C+ + H2(v = 0, 1) reaction are important for estimating the CH+ emission spectra in different astronomical environments. In this study, reactive quantum dynamics of the C+ + H2(v = 0, 1) reaction have been investigated with the time-dependent wave packet method on the high-quality potential energy surface recently developed by Guo et al. The simulated total cross sections are compared in detail with previous experimental measurements and dynamical results. The calculated total rate constants are found to be in good agreement with previous quasi-classical results by Herráez-Aguilar et al., except for the v = 0 reaction at low temperatures. The ro-vibrational state-resolved rate constants show that the CH+ product, obtained from both the v = 0 and v = 1 reactions, is significantly populated in the vibrational ground but rotational excited states. In particular, for the v = 0 reaction, the CH+ product is preferably formed at j' = 4, 5 rotational levels, while the CH+ product for the v = 1 reaction prefers rotational excitation j' = 6-8. This finding varies with previous J-shifting calculations by Zanchet et al., owing to the different potential energy surface and methodology employed in the calculations.

Keywords: astrochemistry; abundance ratios; interstellar medium; theoretical models; molecular physics
H I Gas Playing Hide-and-seek around a Powerful FRI-type Quasar at z 2.1

We present optical spectroscopic and milliarcsecond-scale radio continuum observations of the quasar M1540-1453 (z em = 2.104 ± 0.002) that show associated H I 21 cm absorption at z abs = 2.1139. At subkiloparsec scales, the powerful radio source with 1.4 GHz luminosity of 5.9 × 1027 W Hz-1 shows Fanaroff-Riley class I morphology caused by the interaction with dense gas within 70 pc of the active galactic nucleus (AGN). Interestingly, while there are indications for the presence of absorption from low-ionization species like Fe II, Si II, and Si III in the optical spectrum, the expected strong damped Lyα absorption is not detected at the redshift of the H I 21 cm absorber. In comparison to typical high-z quasars, the Lyα emission line is much narrower. The "ghostly" nature of the H I Lyα absorber partially covering the broad-line region of extent 0.05 pc and the detection of widespread H I 21 cm absorption covering the diffuse radio source (extent >425 pc) imply the presence of a large clumpy H I halo, which may have been blown by the jet-interstellar medium (ISM) interaction. Further observations are needed to confirm the ghostly nature of the Lyα absorber and obtain a better understanding of the role played by the jet-ISM interaction in shaping the radio morphology of this powerful AGN. The study showcases how joint radio and optical analysis can shed light on the gaseous environment and origin of radio morphology in AGNs at high redshifts, when these are still the assembly sites of giant galaxies.

Keywords: active galactic nuclei; radio loud quasars; radio jets; quasar absorption line spectroscopy