adsabs/SciX_UAT_keywords huggingface dataset:
The Discovery and Follow-up of Four Transiting Short-period Sub-Neptunes Orbiting M Dwarfs

Sub-Neptunes with radii of 2–3 R ⊕ are intermediate in size between rocky planets and Neptune-sized planets. The orbital properties and bulk compositions of transiting sub-Neptunes provide clues to the formation and evolution of close-in small planets. In this paper, we present the discovery and follow-up of four sub-Neptunes orbiting M dwarfs (TOI-782, TOI-1448, TOI-2120, and TOI-2406), three of which were newly validated by ground-based follow-up observations and statistical analyses. TOI-782 b, TOI-1448 b, TOI-2120 b, and TOI-2406 b have radii of , , 2.120 ± 0.067 R ⊕, and and orbital periods of P = 8.02, 8.11, 5.80, and 3.08 days, respectively. Doppler monitoring with the Subaru/InfraRed Doppler instrument led to 2σ upper limits on the masses of <19.1 M ⊕, <19.5 M ⊕, <6.8 M ⊕, and <15.6 M ⊕ for TOI-782 b, TOI-1448 b, TOI-2120 b, and TOI-2406 b, respectively. The mass–radius relationship of these four sub-Neptunes testifies to the existence of volatile material in their interiors. These four sub-Neptunes, which are located above the so-called "radius valley," are likely to retain a significant atmosphere and/or an icy mantle on the core, such as a water world. We find that at least three of the four sub-Neptunes (TOI-782 b, TOI-2120 b, and TOI-2406 b), orbiting M dwarfs older than 1 Gyr, are likely to have eccentricities of e ∼ 0.2–0.3. The fact that tidal circularization of their orbits is not achieved over 1 Gyr suggests inefficient tidal dissipation in their interiors.

Keywords: exoplanets; mini neptunes; radial velocity; transit photometry; tides; m dwarf stars
Computational Study of the Hydrogenation Sequence of the Phosphorous Atom on Interstellar Dust Grains

The detection of phosphorous-bearing molecules in interstellar environments constitutes a fundamental task for understanding the formation of prebiotic molecules, but it is also a challenge. In cold interstellar environments, where rich chemistry is expected to happen, only PN and PO have been detected. Phosphine (PH3) must also play an essential role in these regions, since P is expected to deplete onto dust grains significantly, and hydrogenation reactions are dominant in such environments. Surface chemistry on dust grains shows a particular idiosyncrasy where an equilibrium between competitive reactions, photoconversion processes, and desorption are in continuous interplay, modifying both the dust composition and the gas composition. In this study, we theoretically study in detail the interconversion of P to PH3 via subsequent additions of H on cold dust grain analogs. For all reactions, we provide the binding energy of the adsorbates, reaction energies, and, when present, activation barriers and tunneling-corrected rate constants. We also present an estimate of the desorption temperature of these species based on transition state theory. Using recently available experimental results on PH3 desorption via chemical reactions, we conclude that all of the intermediate products of the hydrogenation sequence to phosphine may be released to the gas phase.

Keywords: astrochemistry; pre-biotic astrochemistry; computational methods; molecular clouds; interstellar dust processes
Spectroscopic Survey of Faint Planetary-nebula Nuclei. IV. The A35-type Central Star of Pa 27

We present optical spectroscopy of the 12th-magnitude central star of the planetary nebula (PN) Patchick 27 (Pa 27), obtained during a survey of faint PN nuclei (PNNs) with the Low-Resolution Spectrograph of the Hobby–Eberly Telescope. The optical spectrum of Pa 27 is that of a K0 III red giant with rotationally broadened lines. However, the star is detected in the near-ultraviolet (near-UV) with GALEX, showing that a hot binary component is also present. The spectral-energy distribution from the near-UV to the mid-infrared can be fitted with a combination of the K0 III giant and a hot PNN with an effective temperature of about 50,000 K. Photometric observations of Pa 27, both ground-based and from TESS, show a low-amplitude sinusoidal variation with a period of 7.36 days, probably due to starspots on a rotating and magnetically active cool giant. Pa 27 is a new member of the rare class of "A35-type central stars," which are binary PNNs consisting of a spotted late-type star and a hot pre–white dwarf. They are likely the result of a situation where an asymptotic-giant-branch (AGB) star ejects its outer layers in a dense wind, part of which is captured by a distant companion, spinning up its rotation by accretion of material and angular momentum. We suggest several useful follow-up observations. *Based on observations obtained with the Hobby–Eberly Telescope (HET), which is a joint project of the University of Texas at Austin, the Pennsylvania State University, Ludwig-Maximillians-Universität München, and Georg-August Universität Göttingen. The HET is named in honor of its principal benefactors, William P. Hobby and Robert E. Eberly.

Keywords: planetary nebulae; planetary nebulae nuclei; starspots; stellar rotation; detached binary stars
Infrared Observations of 2I/Borisov near Perihelion

As the first interstellar comet, 2I/Borisov provides a unique opportunity to study the surface composition of a comet from another stellar system, particularly whether it has water ice. In order to investigate the nature of 2I/Borisov, we conducted infrared observations close to perihelion. The water ice, if present, is expected to be revealed by absorption features at 1.5 and 2 micron. We therefore used FLAMINGOS-2 mounted on the Gemini south telescope, to carry out deep imaging on 2019 November 30 UT and spectroscopy on 2019 December 7 UT. At first glance, our imaging did not reveal an apparent coma or a cometary tail. This is due to the bright sky background and our short exposure times. Nevertheless we were able to put an upper limit of the size of the nucleus, as well as provide high-precision astrometry that can be used to investigate nongravitational acceleration in the future. Our infrared spectra showed a negative slope, contrary to the results by Yang et al. It is not unheard of for a comet to show a negative slope, and to progressively exhibit a spectrum with decreasing slope. Possible causes of the decreasing slope are an increase in water ice and/or decrease in dust size. Given the fact that our observations were carried out close to perihelion, it is likely that both factors contribute to the decreasing, negative slope of the infrared spectrum.

Keywords: comets
Predicting the Yields of z > 6.5 Quasar Surveys in the Era of Roman and Rubin

About 70 luminous quasars discovered at z > 6.5 are strongly biased toward the bright end, thus not providing a comprehensive view of quasar abundance beyond the cosmic dawn. We present the predicted results of the Roman/Rubin high-redshift quasar survey, yielding 3 times more, 2-4 mag deeper quasar samples, probing high-redshift quasars across a broad range of luminosities, especially faint quasars at L bol ~ 1010 L ⊙ or M 1450 ~ -22, which are currently poorly explored. We include high-z quasars, galactic dwarfs, and low-z compact galaxies with similar colors as quasar candidates. We create mock catalogs based on population models to evaluate selection completeness and efficiency. We utilize the classical color dropout method in the z and Y bands to select primary quasar candidates, followed up with the Bayesian selection method to identify quasars. We show that overall selection completeness >80% and efficiency ~10% at 6.5 < z < 9, with 180 quasars at z > 6.5, 20 at z > 7.5, and 2 at z > 8.5. The quasar yields depend sensitively on the assumed quasar luminosity shape and redshift evolution. Brown dwarf rejection through proper motion up to 50% can be made for stars brighter than 25 mag, low-z galaxies dominate at fainter magnitude. Our results show that Roman/Rubin are able to discover a statistical sample of the earliest and faintest quasars in the Universe. The new valuable data sets are worth follow-up studies with JWST and Extremely Large Telescopes to determine the quasar luminosity function faint end slope and constraint the supermassive black holes growth in the early Universe.

Keywords: quasars; supermassive black holes; wide-field telescopes
Cloud-convection Feedback in Brown Dwarf Atmospheres

Numerous observational evidence has suggested the presence of active meteorology in the atmospheres of brown dwarfs. A near-infrared brightness variability has been observed. Clouds have a major role in shaping the thermal structure and spectral properties of these atmospheres. The mechanism of such variability is still unclear, and neither 1D nor global circulation models can fully study this topic due to resolution. In this study, a convective-resolving model is coupled to gray-band radiative transfer in order to study the coupling between the convective atmosphere and the variability of clouds over a large temperature range with a domain of several hundred kilometers. Six types of clouds are considered, with microphysics including settling. The clouds are radiatively active through the Rosseland mean coefficient. Radiative cloud feedback can drive spontaneous atmospheric variability in both temperature and cloud structure, as modeled for the first time in three dimensions. Silicate clouds have the most effect on the thermal structure with the generation of a secondary convective layer in some cases, depending on the assumed particle size. Iron and aluminum clouds also have a substantial impact on the atmosphere. Thermal spectra were computed, and we find the strongest effect of the clouds is the smoothing of spectral features at optical wavelengths. Compared to observed L and T dwarfs on the color-magnitude diagram, the simulated atmospheres are redder for most of the cases. Simulations with the presence of cloud holes are closer to observations.

Keywords: brown dwarfs
Three-dimensional Particle-in-cell Simulations of the Solar Wind Interaction with Asteroid 2016 HO3

The recently discovered asteroid 2016 HO3 is the most stable quasi-satellite of our Earth. Several missions to 2016 HO3 have been proposed, including the Tianwen-2 mission of China. Here we study the solar wind interaction with 2016 HO3 with three-dimensional particle-in-cell simulations. It is found that the sunlit surface can be positively charged to more than +10 V, and the shadowed surface is negatively charged to lower than -30 V. The typical electric field on the sunlit surface is about 2 V m-1 but can increase up to 20 V m-1 near the terminator. There is a plasma wake behind 2016 HO3 with a reduced plasma density. Normally, the ion density can be reduced to about 0.3 of the solar wind density at 100 m downstream from 2016 HO3, and the plasma wake is confined by a Mach cone with a cone angle of about 6.°5. In addition, we find that both the solar wind parameters and the secondary electron emission can affect the surface charging, which, in return, changes the wake structure.

Keywords: solar wind; asteroids
Debris Disks Can Contaminate Mid-infrared Exoplanet Spectra: Evidence for a Circumstellar Debris Disk around Exoplanet Host WASP-39

The signal from a transiting planet can be diluted by astrophysical contamination. In the case of circumstellar debris disks, this contamination could start in the mid-infrared and vary as a function of wavelength, which would then change the observed transmission spectrum for any planet in the system. The MIRI/Low Resolution Spectrometer WASP-39b transmission spectrum shows an unexplained dip starting at ∼10 μm that could be caused by astrophysical contamination. The spectral energy distribution displays excess flux at similar levels to that which are needed to create the dip in the transmission spectrum. In this Letter, we show that this dip is consistent with the presence of a bright circumstellar debris disk, at a distance of >2 au. We discuss how a circumstellar debris disk like that could affect the atmosphere of WASP-39b. We also show that even faint debris disks can be a source of contamination in MIRI exoplanet spectra.

Keywords: debris disks; exoplanet atmospheres; infrared spectroscopy; spectral energy distribution; circumstellar dust; exoplanet evolution; exoplanet atmospheric composition
Magnetohydrodynamic Simulations of the Supernova Remnant G1.9+0.3

The youngest Galactic supernova remnant G1.9+0.3 shows a discrete feature between its radio and X-ray morphologies. The observed radio morphology features a single maximum in the north, while the X-ray observation shows two opposite "ears" on the east and west sides. Using 3D magnetohydrodynamical simulations, we investigate the formation of the discrete feature of the remnant. We have tested different parameters for better simulation and reproduced similar discrete features under an environment with a density gradient and an environment with clump, which provides a possible explanation of the observation.

Keywords: supernova remnants; magnetohydrodynamical simulations
Structure of the W3A Low-density Foreground Region

We present analysis of [O I] 63 μm and CO J = 5 - 4 and 8 - 7 multiposition data in the W3A region and use it to develop a model for the extended low-density foreground gas that produces absorption features in the [O I] and J = 5 - 4 CO lines. We employ the extinction to the exciting stars of the background H II region to constrain the total column density of the foreground gas. We have used the Meudon photodissociation region code to model the physical conditions and chemistry in the region employing a two-component model with a high-density layer near the H II region responsible for the fine-structure line emission and an extended low-density foreground layer. The best-fitting total proton density, constrained largely by the CO lines, is n(H) = 250 cm-3 in the foreground gas and 5 × 105 cm-3 in the material near the H II region. The absorption is distributed over the region mapped in W3A and is not restricted to the foreground of either the embedded exciting stars of the H II region or the protostar W3 IRS5. The low-density material associated with regions of massive-star formation, based on an earlier study by Goldsmith et al., is quite common, and we now see that it is extended over a significant portion of W3A. It thus should be included in modeling of fine-structure line emission, including interpreting low-velocity-resolution observations made with incoherent spectrometer systems, in order to use these lines as accurate tracers of massive-star formation.

Keywords: star formation; photodissociation regions; giant molecular clouds; submillimeter astronomy
Toward Robust Corrections for Stellar Contamination in JWST Exoplanet Transmission Spectra

Transmission spectroscopy is still the preferred characterization technique for exoplanet atmospheres, although it presents unique challenges that translate into characterization bottlenecks when robust mitigation strategies are missing. Stellar contamination is one such challenge that can overpower the planetary signal by up to an order of magnitude, and thus not accounting for it can lead to significant biases in the derived atmospheric properties. Yet this accounting may not be straightforward, as important discrepancies exist between state-of-the-art stellar models and measured spectra and between models themselves. Here we explore the extent to which stellar models can be used to reliably correct for stellar contamination and yield a planet's uncontaminated transmission spectrum. We find that discrepancies between stellar models can significantly contribute to the noise budget of JWST transmission spectra of planets around stars with heterogeneous photospheres, the true number of unique photospheric spectral components and their properties can only be accurately retrieved when the stellar models have sufficient fidelity, and under such optimistic circumstances the contribution of stellar contamination to the noise budget of a transmission spectrum is considerably below that of the photon noise for the standard transit observation setup. Therefore, we advocate for further development of model spectra of stars and their active regions in a data-driven manner, empirical approaches for deriving spectra of photospheric components using the observatories with which the atmospheric explorations are carried out, and analysis techniques accounting for multimodal posterior distributions for photospheric parameters of interest, which will be increasingly revealed by precise JWST measurements.

Keywords: transmission spectroscopy; stellar atmospheres; planet hosting stars; exoplanet atmospheres; fundamental parameters of stars; starspots
A 3D Parametric Martian Bow Shock Model with the Effects of Mach Number, Dynamic Pressure, and the Interplanetary Magnetic Field

Using global MHD simulations, we construct a 3D parametric Martian bow shock model that employs a generalized conic section function defined by seven parameters. Effects of the solar wind dynamic pressure (Pd), the magnetosonic Mach number (MMS), and the intensity and the orientation of the interplanetary magnetic field (IMF) on the seven parameters are examined based on 250 simulation cases. These 250 cases have a Pd range of 0.36-9.0 nPa (the solar wind number density varying from 3.5 to 12 cm-3 and the solar wind speed varying from 250 to 670 km s-1), an MMS range of 2.8-7.9, and an IMF strength range from zero to 10 nT. The results from our parametric model show several things. (1) The size of the Martian bow shock is dominated by Pd. When Pd increases, the bow shock moves closer to Mars, and the flaring of the bow shock decreases. (2) The MMS has a similar effect on the bow shock as Pd but with different coefficients. (3) The effects of IMF components on the bow shock position are associated with the draping and pileup of the IMF around the Martian ionosphere; hence, we find that both the subsolar standoff distance and the flaring angle of the bow shock increase with the field strength of the IMF components that are perpendicular to the solar wind flow direction (BY and BZ in the MSO coordinate system). The parallel IMF component (BX) has little effect on the subsolar standoff distance but affects the flaring angle. (4) The cross section of the bow shock is elongated in the direction perpendicular to the IMF on the Y-Z plane, and the elongation degree is enhanced with increasing intensities of BY and BZ. The north-south (dawn-dusk) asymmetry is controlled by the cone angle when the IMF is on the X-Z (X-Y) plane. These results show a good agreement with the previous empirical and theoretical models. The current parametric model is obtained under solar maximum conditions with the strongest Martian crustal magnetic field located at the subsolar point. In fact, the bow shock shape can also be affected by both the solar extreme ultraviolet radiation and the orientation of crustal magnetic anomalies to the Sun, which should be considered in future models.

Keywords: planetary bow shocks; interplanetary magnetic fields; mars; solar wind
The Radius of PSR J0740+6620 from NICER and XMM-Newton Data

PSR J0740+6620 has a gravitational mass of 2.08 ± 0.07 M⊙, which is the highest reliably determined mass of any neutron star. As a result, a measurement of its radius will provide unique insight into the properties of neutron star core matter at high densities. Here we report a radius measurement based on fits of rotating hot spot patterns to Neutron Star Interior Composition Explorer (NICER) and X-ray Multi-Mirror (XMM-Newton) X-ray observations. We find that the equatorial circumferential radius of PSR J0740+6620 is ${13.7}_{-1.5}^{+2.6}$ km (68%). We apply our measurement, combined with the previous NICER mass and radius measurement of PSR J0030+0451, the masses of two other ~2 M⊙ pulsars, and the tidal deformability constraints from two gravitational wave events, to three different frameworks for equation-of-state modeling, and find consistent results at ~1.5-5 times nuclear saturation density. For a given framework, when all measurements are included, the radius of a 1.4 M⊙ neutron star is known to ±4% (68% credibility) and the radius of a 2.08 M⊙ neutron star is known to ±5%. The full radius range that spans the ±1σ credible intervals of all the radius estimates in the three frameworks is 12.45 ± 0.65 km for a 1.4 M⊙ neutron star and 12.35 ± 0.75 km for a 2.08 M⊙ neutron star.

Keywords: x-ray sources; millisecond pulsars; neutron stars; neutron star cores
Whether Small Flux Ropes and Magnetic Clouds Have the Same Origin: A Statistical Study of Small Flux Ropes in Different Types of Solar Wind

According to the duration and size, magnetic flux ropes can be divided into large-scale flux ropes, namely, magnetic clouds, and small-scale flux ropes (SFRs). Whether SFRs have the same origin as magnetic clouds has been a hot topic for a long time. Based on the SFR database developed by Hu et al. and Chen et al., this paper analyzes the properties of SFRs in different types of solar wind, which are SFRs in interplanetary coronal mass ejections (ICMEs), SFRs in stream interaction regions, and SFRs in background solar wind. On the assumption that SFRs in ICMEs have the same origin as magnetic clouds, we compare the three types of SFRs from several aspects, attempting to shed some light on the dispute, i.e., whether SFRs are homologous to magnetic clouds. The results show that up to 91% of the SFRs are outside ICMEs. Unlike SFRs in ICMEs, SFRs outside ICMEs seldom have large magnetic field strength and apparent expansion signatures. In addition, 36% of the SFRs in ICMEs have enhanced iron charge states. This probability is much higher than the other two types of SFRs. By an automatic method, this paper also find that counterstreaming electrons are more common in SFRs in ICMEs. Considering strong magnetic field, expansion signatures, large iron charge state, and counterstreaming electrons are important indicators of magnetic clouds, we believe that most of the SFRs near Earth have different origins from magnetic clouds.

Keywords: interplanetary magnetic fields; solar wind; solar coronal mass ejections