adsabs/SciX_UAT_keywords huggingface dataset:
Proton Temperature Anisotropy Variations in Inner Heliosphere Estimated with the First Parker Solar Probe Observations

We present a technique for deriving the temperature anisotropy of solar wind protons observed by the Parker Solar Probe (PSP) mission in the near-Sun solar wind. The radial proton temperature measured by the Solar Wind Electrons, Alphas, and Protons (SWEAP) Solar Probe Cup is compared with the orientation of local magnetic field measured by the FIELDS fluxgate magnetometer, and the proton temperatures parallel and perpendicular to the magnetic field are extracted. This procedure is applied to different data products, and the results are compared and optimum timescales for data selection and trends in the uncertainty in the method are identified. We find that the moment-based proton temperature anisotropy is more physically consistent with the expected limits of the mirror and firehose instabilities, possibly because the nonlinear fits do not capture a significant non-Maxwellian shape to the proton velocity distribution function near the Sun. The proton beam has a small effect on total proton temperature anisotropy owing to its much smaller density relative to the core compared to what was seen by previous spacecraft farther from the Sun. Several radial trends in the temperature components and the variation of the anisotropy with parallel plasma beta are presented. Our results suggest that we may see stronger anisotropic heating as PSP moves closer to the Sun, and that a careful treatment of the shape of the proton distribution may be needed to correctly describe the temperature.

Keywords: solar wind; solar coronal heating; space plasmas
Competitive Dehydrogenation and Backbone Fragmentation of Superhydrogenated PAHs: A Laboratory Study

Superhydrogenated polycyclic aromatic hydrocarbons (PAHs) have been suggested to catalyze the formation of H2 in certain regions of space, but it remains unclear under which circumstances this mechanism is viable given the reduced carbon backbone stability of superhydrogenated PAHs. We report a laboratory study on the stability of the smallest pericondensed PAH, pyrene (C16H10+N, with N = 4, 6, and 16 additional H atoms), against photodestruction by single vacuum ultraviolet photons using the photoelectron-photoion coincidence technique. For N = 4, we observe a protective effect of hydrogenation against the loss of native hydrogens, in the form of an increase in the appearance energies of the ${{\rm{C}}}_{16}{{\rm{H}}}_{9}^{+}$ and C16H8+ daughter ions compared to those reported for pristine pyrene (C16H10). No such effect is seen for N = 6 or 16, where the weakening effect of replacing aromatic bonds with aliphatic ones outweighs the buffering effect of the additional hydrogen atoms. The onset of fragmentation occurs at similar internal energies for N = 4 and 6, but is significantly lower for N = 16. In all three cases, H-loss and CmHn-loss (m ≥ 1, carbon backbone fragmentation) channels open at approximately the same energy. The branching fractions of the primary channels favor H-loss for N = 4, CmHn-loss for N = 16, and are roughly equal for the intermediate N = 6. We conclude that superhydrogenated pyrene is probably too small to support catalytic H2-formation, while trends in the current and previously reported data suggest that larger PAHs may serve as catalysts up to a certain level of hydrogenation.

Keywords: polycyclic aromatic hydrocarbons; astrochemistry; laboratory astrophysics; photodissociation regions; reaction catalysts
The Contribution of Electrons to the Sputter-produced O2 Exosphere on Europa

Electrons contribute a strong radiation component to the surface bombardment of Europa. However, they are not typically considered to contribute to erosion of the surface H2O-ice or produce exospheres of radiolytic O2, as laboratory studies on sputtering induced by electrons are sparse. Here we have measured the sputtering yield of H2O-ice induced by 0.5 keV electrons between 14 and 125 K, estimating the composition of the stable products ejected during irradiation. Combining these measurements with updated electron flux measurements, we estimate for the first time that the global surface production rate of O2 from electron-induced sputtering is larger than the production rate previously estimated for all of the ionic components combined. Our results emphasize the importance of electrons in producing exospheres on icy satellites and suggest that these exospheres need not be tied to environments where the surface is being bombarded with heavy ions.

Keywords: astrochemistry; laboratory astrophysics; surface ices; galilean satellites; jovian satellites; exosphere; cosmic rays; solid matter physics; spectroscopy
Environmental Influences on Star Formation in Low-mass Galaxies Observed by the SDSS-IV/MaNGA Survey

We explore the environmental influences on the star formation (SF) in low-mass galaxies with stellar mass 8 ≤ log(M⋆/M⊙) ≤ 10 at a redshift of 0.01 < z < 0.07. We identify the neighboring galaxies for our sample using the spectroscopically observed galaxies in the Sloan Digital Sky Survey (SDSS). Our 287 selected pair candidates have a neighboring galaxy with a stellar mass ratio of MNeighbor/MCandidate ≤ 4 at a projected separation within dproj ≤ 1500 kpc and a line-of-sight kinematic separation of ΔVLOS ≤ 300 km s-1. Our control galaxies are isolated from other galaxies within a projected radius of 1500 kpc. All selected galaxies in our sample are spectroscopically observed by the fourth generation of SDSS/Mapping Nearby Galaxies at Apache Point Observatory (SDSS-IV/MaNGA) integral field spectroscopy survey. We radially bin our selected galaxies into three regions with a radial distance of 0 ≤ R/Re ≤ 0.5 (inner), 0.5 ≤ R/Re ≤ 1.0 (middle), and 1.0 ≤ R/Re ≤ 1.5 (outer), in which Re is the effective radius at where the galaxy emit half of its light. We conclude that the SF activities in low-mass galaxies are affected by their environmental conditions when ΔVLOS ≤ 100 km s-1 at dproj ≤ 400 kpc. We use stellar-mass-weighted SF rate surface density ( ${\rm{\Sigma }}\mathrm{SFR}/{M}_{\star }$ ) to describe the SF strength in each radially binned region. For the pair candidates with 0.25 ≤ MNeighbor/MCandidate ≤ 4 at dproj ≤ 100 kpc and ${\rm{\Delta }}{V}_{\mathrm{LOS}}\leqslant 100\,\mathrm{km}\,{{\rm{s}}}^{-1}$ , we observe an SF enhancement of ${f}_{{\rm{\Delta }}\mathrm{SF}}=1.75\pm 0.96$ ( ${f}_{{\rm{\Delta }}\mathrm{SF}}$ = $[{({\rm{\Sigma }}\mathrm{SFR}/{M}_{\star })}_{\mathrm{Pair}}-{({\rm{\Sigma }}\mathrm{SFR}/{M}_{\star })}_{\mathrm{Control},\mathrm{mean}}]$ / ${({\rm{\Sigma }}\mathrm{SFR}/{M}_{\star })}_{\mathrm{Control},\mathrm{mean}}$ ) in their inner regions, which decreases with increasing galactic radii.

Keywords: galaxy evolution; galaxy interactions; dwarf galaxies; star formation
Inferences on Relations between Distant Supermassive Black Holes and Their Hosts Complemented by the Galaxy Fundamental Plane

The realization of fundamental relations between supermassive black holes and their host galaxies would have profound implications in astrophysics. To add further context to studies of their coevolution, an investigation is carried out to gain insight as to whether quasars and their hosts at earlier epochs follow the local relation between black hole mass (M BH) and stellar velocity dispersion (σ *). We use 584 Sloan Digital Sky Survey quasars at 0.2 < z < 0.8 with black hole measurements and properties of their hosts from the Hyper Suprime-Cam Subaru Strategic Program. An inference of σ * is achieved for each based on the total stellar mass (M *) and size of the host galaxy by using the galaxy mass fundamental plane for inactive galaxies at similar redshifts. In agreement with past studies, quasars occupy elevated positions from the local M BH-σ * relation which can be considered as a flattening of the relation. Based on a simulated sample, we demonstrate that an evolving intrinsic M BH-σ * relation can match the observations. However, we hypothesize that these changes are simply a consequence of a nonevolving intrinsic relationship between M BH and M *. Reassuringly, there is evidence of migration onto the local M BH-σ * for galaxies that are either massive, quiescent or compact. Thus, the bulges of quasar hosts at high redshift are growing and likely to align onto the mass scaling relation with their black holes at later times.

Keywords: quasars; agn host galaxies; active galactic nuclei
A SUBLIME 3D Model for Cometary Coma Emission: The Hypervolatile-rich Comet C/2016 R2 (PanSTARRS)

The coma of comet C/2016 R2 (PanSTARRS) is one of the most chemically peculiar ever observed, in particular due to its extremely high CO/H2O and ${{\rm{N}}}_{2}^{+}$ /H2O ratios, and unusual trace volatile abundances. However, the complex shape of its CO emission lines, as well as uncertainties in the coma structure and excitation, has lead to ambiguities in the total CO production rate. We performed high-resolution, spatially, spectrally, and temporally resolved CO observations using the James Clerk Maxwell Telescope and Submillimeter Array to elucidate the outgassing behavior of C/2016 R2. Results are analyzed using a new, time-dependent, three-dimensional radiative transfer code (SUBlimating gases in LIME; SUBLIME, based on the open-source version of the LIne Modeling Engine), incorporating for the first time, accurate state-to-state collisional rate coefficients for the CO-CO system. The total CO production rate was found to be in the range of (3.8 - 7.6) × 1028 s-1 between 2018 January 13 and February 1 (at r H = 2.8-2.9 au), with a mean value of (5.3 ± 0.6) × 1028 s-1. The emission is concentrated in a near-sunward jet, with a half-opening angle of ~62° and an outflow velocity of 0.51 ± 0.01 km s-1, compared to 0.25 ± 0.01 km s-1 in the ambient (and nightside) coma. Evidence was also found for an extended source of CO emission, possibly due to icy grain sublimation around 1.2 × 105 km from the nucleus. Based on the coma molecular abundances, we propose that the nucleus ices of C/2016 R2 can be divided into a rapidly sublimating apolar phase, rich in CO, CO2, N2, and CH3OH, and a predominantly frozen (or less abundant), polar phase containing more H2O, CH4, H2CO, and HCN.

Keywords: comets; long period comets; submillimeter astronomy; comet volatiles; high resolution spectroscopy; radio interferometry; radiative transfer simulations; de-excitation rates
TRAPPIST-1h as an Exo-Titan. I. The Role of Assumptions about Atmospheric Parameters in Understanding an Exoplanet Atmosphere

The TRAPPIST-1 system is home to at least seven terrestrial planets and is a target of interest for future James Webb Space Telescope (JWST) observations. Additionally, these planets will be of interest to future missions making observations in the ultraviolet (UV). Although several of these planets are located in the traditional habitable zone, where liquid water could exist on the surface, TRAPPIST-1h is interesting to explore as a potentially habitable ocean world analog. In this study, we evaluate the observability of a Titan-like atmosphere on TRAPPIST-1h. The ability of the JWST or a future UV mission to detect specific species in the atmosphere at TRAPPIST-1h will depend on how far each species extends from the surface. In order to understand the conditions required for detection, we evaluate the input parameters used in one-dimensional models to simulate the structure of Titan-like atmospheres. These parameters include surface temperature and pressure, temperature profile as a function of distance from the surface, composition of the minor species relative to N2, and the eddy diffusion coefficient. We find that JWST simulated spectra for cloud- and haze-free atmospheres are most sensitive to surface temperature, temperature gradients with altitude, and surface pressure. The importance of temperature gradients in JWST observations shows that a simple isothermal scale height is not ideal for determining temperature or atmospheric mean molecular mass in transit spectra from exoplanet atmospheres. We demonstrate that UV transmission spectra are sensitive to the upper atmosphere, where the exobase can be used to approximate the vertical extent of the atmosphere.

Keywords: planetary atmospheres; exoplanet atmospheres
Double Asteroid Redirection Test (DART): Structural and Dynamic Interactions between Asteroidal Elements of Binary Asteroid (65803) Didymos

NASA's Double Asteroid Redirection Test (DART) mission is the first full-scale planetary defense mission. The target is the binary asteroid (65803) Didymos, in which the smaller component Dimorphos (~164 m equivalent diameter) orbits the larger component Didymos (~780 m equivalent diameter). The DART spacecraft will impact Dimorphos, changing the system's mutual orbit by an amount that correlates with DART's kinetic deflection capability. The spacecraft collision with Dimorphos creates an impact crater, which reshapes the body. Also, some particles ejected from the DART impact site on Dimorphos eventually reach Didymos. Because Didymos's rapid spin period (2.26 hr) may be close to its stability limit for structural failure, the ejecta reaching Didymos may induce surface disturbance on Didymos. While large uncertainties exist, nonnegligible reshaping scenarios on Didymos and Dimorphos are possible if certain conditions are met. Our analysis shows that given a surface slope uncertainty on Dimorphos of 45°, with no other information about its local topography, and if the DART-like impactor is treated as spherical, the ejecta cone crosses Didymos with speeds ≳14 m s-1 in 13% of simulations. Additional work is necessary to determine the amount of mass delivered to Didymos from the DART impact and whether the amount of kinetic energy delivered is sufficient to overcome cohesive forces in those cases. If nonnegligible (but small) reshaping occurs for either of these asteroids, the resulting orbit perturbation and reshaping are measurable by Earth-based observations.

Keywords: asteroids; near-earth objects
A Search for FeH in Hot-Jupiter Atmospheres with High-dispersion Spectroscopy

Most of the molecules detected thus far in exoplanet atmospheres, such as water and CO, are present for a large range of pressures and temperatures. In contrast, metal hydrides exist in much more specific regimes of parameter space, and so can be used as probes of atmospheric conditions. Iron hydride (FeH) is a dominant source of opacity in low-mass stars and brown dwarfs, and evidence for its existence in exoplanets has recently been observed at low resolution. We performed a systematic search of archival CARMENES near-infrared data for signatures of FeH during transits of 12 exoplanets. These planets span a large range of equilibrium temperatures (600 $\lesssim \,{T}_{\mathrm{eq}}\,\lesssim $ 4000 K) and surface gravities (2.5 $\lesssim \,\mathrm{log}g\,\lesssim $ 3.5). We did not find a statistically significant FeH signal in any of the atmospheres, but obtained potential low-confidence signals (signal-to-noise ratio ∼ 3) in two planets, WASP-33b and MASCARA-2b. Previous modeling of exoplanet atmospheres indicate that the highest volume mixing ratios (VMRs) of 10-7 to 10-9 are expected for temperatures between 1800 and 3000 K and log $g\gtrsim 3$ . The two planets for which we find low-confidence signals are in the regime where strong FeH absorption is expected. We performed injection and recovery tests for each planet and determined that FeH would be detected in every planet for VMRs $\geqslant {10}^{-6}$ , and could be detected in some planets for VMRs as low as ${10}^{-9.5}$ . Additional observations are necessary to conclusively detect FeH and assess its role in the temperature structures of hot-Jupiter atmospheres.

Keywords: exoplanet atmospheres; exoplanet atmospheric composition; exoplanets; high resolution spectroscopy; hot jupiters
Investigation of Orbital Decay and Global Modeling of the Planet WASP-43 b

WASP-43 b is one of the most important candidates for detecting an orbital decay. We investigate pieces of evidence for this expectation as variations in its transit timings, based on the ground and space observations. The data set includes the transit observations at the TÜBİTAK National Observatory of Turkey and Transiting Exoplanet Survey Satellite (TESS). We present a global model of the system, based on the most precise photometry from space, ground, and archival radial velocity data. Using the homogenized data set and modeled light curves, we measure the mid-transit times for WASP-43 b. Our analysis agrees with a linear ephemeris for which we refine the light elements for future observations of the system. However, there is a negative difference between the transit timings derived from TESS data in two sectors (9 and 35) and a hint of an orbital period decrease in the entire data set. Both findings are statistically insignificant due to the short baseline of observations, which prevents us from drawing firm conclusions about the orbital decay of this ultra-short-period planet. However, assuming the effect of this decrease of the period in the planet's orbit, we derive a lower limit for the reduced tidal quality factor as ${Q}_{* }^{{\prime} }\gt (4.01\pm 1.15)\times {10}^{5}$ from the best-fitting quadratic function. Finally, we calculate a probable rotational period for this system as 7.52 days from the out-of-transit flux variation in the TESS light curves due to spot modulation.

Keywords: exoplanet systems; hot jupiters; exoplanets
The Discovery of Nulling and Mode-switching Pulsars with CHIME/Pulsar

The Pulsar backend of the Canadian Hydrogen Intensity Mapping Experiment has monitored hundreds of known pulsars in the northern sky since fall 2018, providing a rich data set for the study of temporal variations in pulsar emission. Using a matched filtering technique, we report, for the first time, nulling behavior in five pulsars as well as mode switching in nine pulsars. Only one of the pulsars is observed to show both nulling and moding signals. These new nulling and mode-switching pulsars appear to come from a population with relatively long spin periods, in agreement with previous findings in the literature.

Keywords: pulsars; radio astronomy; astronomical methods; observational astronomy; neutron stars
The X-Ray Cavity Around Hotspot E in Cygnus A: Tunneled by a Deflected Jet

The powerful Fanaroff-Riley class II (FR II) radio galaxy Cygnus A exhibits primary and secondary hotspots in each lobe. A 2 Ms Chandra X-ray image of Cygnus A has revealed an approximately circular hole, with a radius of 3.9 kpc, centered on the primary hotspot in the eastern radio lobe, hotspot E. We infer the distribution of X-ray emission on our line of sight from an X-ray surface brightness profile of the radio lobe adjacent to the hole and use it to argue that the hole is excavated from the radio lobe. The surface brightness profile of the hole implies a depth at least 1.7 ± 0.3 times greater than its projected width, requiring a minimum depth of 13.3 ± 2.3 kpc. A similar hole observed in the 5 GHz Very Large Array radio map reinforces the argument for a cavity lying within the lobe. We argue that the jet encounters the shock compressed intracluster medium at hotspot E, passing through one or more shocks as it is deflected back into the radio lobe. The orientation of Cygnus A allows the outflow from hotspot E to travel almost directly away from us, creating an elongated cavity, as observed. These results favor models for multiple hotspots in which an FR II jet is deflected at a primary hotspot, then travels onward to deposit the bulk of its power at a secondary hotspot, rather than the dentist drill model.

Keywords: active galaxies; cool cores; galaxy jets; x-ray sources
Annotated Coadds: Concise Metrics for Characterizing Survey Cadence and for Discovering Variable and Transient Sources

In order to study transient phenomena in the Universe, existing and forthcoming imaging surveys are covering wide areas of sky repeatedly over time, with a range of cadences, point spread functions, and depths. We describe here a framework that allows an efficient search for different types of time-varying astrophysical phenomena in current and future, large data repositories. We first present a methodology to generate and store key survey parameters that enable researchers to determine if a survey, or a combination of surveys, allows specific time-variable astrophysical phenomena to be discovered. To facilitate further exploration of sources in regions of interest, we then generate a few sample metrics that capture the essential brightness characteristics of a sky pixel at a specific wavelength. Together, we refer to these as "annotated coadds." The techniques presented here for WISE/NEOWISE-R data are sensitive to 10% brightness variations at around 12th Vega magnitude at 4.5 μm wavelength. Application of the technique to Zwicky Transient Factory data also enabled the detection of 0.5 mag variability at 20 AB mag in the r-band. We demonstrate the capabilities of these metrics for different classes of sources: high proper-motion stars, periodic variable stars, and supernovae, and find that each metric has its advantages depending on the nature of variability. We also present a data structure which will ease the search for temporally varying phenomena in future surveys.

Keywords: time domain astronomy; astronomy data reduction; astronomical techniques; sky surveys
When were the First Exocontinents?

Earth's biosphere was able to increase as continents emerged. I assess when continents could first appear on hypothetical rocky planets of nearby stars. Radiogenic heating of the planetary mantle is evaluated through stellar abundances of iron and silicon (core and mantle proxies) and thorium and potassium (mantle heating proxies). The heat per unit mantle mass is compared to a threshold on Earth after which large-scale continents appeared. Longer delays are inferred for some exoplanets, particularly those with high thorium, but earliest continents could have arisen 2 Gyr before those on Earth, among thin disk stars. In the thick disk, continents could appear 4-5 Gyr pre-Earth. Hence, subsolar-metalicity systems could be an important focus in searching for planets where life could be more advanced than on Earth. At least ~2 worlds with such old continents are expected to be accessible to future space telescopes, such as Habitable Worlds Observatory.

Keywords: stellar abundances; exoplanet plate tectonics; astrobiology