adsabs/SciX_UAT_keywords huggingface dataset:
Reflected Spectroscopy of Small Exoplanets I: Determining the Atmospheric Composition of Sub-Neptunes Planets

Direct imaging of widely separated exoplanets from space will obtain their reflected light spectra and measure their atmospheric properties, and small and temperate planets will be the focus for the next generation of telescopes. In this work, we used our Bayesian retrieval algorithm ${{\rm\small{EXOREL}}}^{{\mathfrak{R}}}$ to determine the constraints on the atmospheric properties of sub-Neptune planets from observations taken with a HabEx-like telescope. Small and temperate planets may have a non-H2-dominated atmosphere, and therefore we introduced the compositional analysis technique in our framework to explore the bulk atmospheric chemistry composition without any prior knowledge about it. We have developed a novel set of prior functions for the compositional analysis free parameters. We compared the performances of the framework with the flat prior and the novel prior and we reported a better performance when using the novel priors set. We found that the retrieval algorithm cannot only identify the dominant gas of the atmosphere but also to constrain other less abundant gases with high statistical confidence without any prior information on the composition. The results presented here demonstrates that reflected light spectroscopy can characterize small exoplanets with diverse atmospheric composition. The Bayesian framework should be applied to design the instrument and the observation plan of exoplanet direct-imaging experiments in the future.

Keywords: exoplanet atmospheric composition; exoplanet atmospheres; bayesian statistics; bayes' theorem; posterior distribution; prior distribution; ocean planets
Robust Absolute Solar Flux Density Calibration for the Murchison Widefield Array

Sensitive radio instruments are optimized for observing faint astronomical sources, and usually need to attenuate the received signal when observing the Sun. There are only a handful of flux density calibrators that can comfortably be observed with the same attenuation setup as the Sun. Additionally, for wide field-of-view (FoV) instruments like the Murchison Widefield Array (MWA) calibrator observations are generally done when the Sun is below the horizon, to avoid the contamination from solar emissions. These considerations imply that the usual radio interferometric approach to flux density calibration is not applicable for solar imaging. A novel technique, relying on a good sky model and detailed characterization of the MWA hardware, was developed for solar flux density calibration for MWA. Though successful, this technique is not general enough to be extended to the data from the extended configuration of the MWA Phase II. Here, we present a robust flux density calibration method for solar observations with MWA independent of the array configuration. We use different approaches-the serendipitous presence of strong sources; detection of numerous background sources using high dynamic range images in the FoV along with the Sun; and observations of strong flux density calibrators with and without the additional attenuation used for solar observations-to obtain the flux scaling parameters required for the flux density calibration. Using the present method, we have achieved an absolute flux density uncertainty ~10% for solar observations even in the absence of dedicated calibrator observations.

Keywords: solar radio telescopes; radio telescopes; flux calibration; solar physics
Direct Statistical Constraints on the Natal Kick Velocity of a Black Hole in an X-Ray Quiet Binary

In recent years, a handful of "dark" binaries have been discovered with a nonluminous compact object. Astrometry and radial velocity measurements of the bright companion allow us to measure the post-supernova orbital elements of such a binary. In this paper, we develop a statistical formalism to use such measurements to infer the pre-supernova orbital elements, and the natal kick imparted by the supernova (SN). We apply this formalism to the recent discovery of an X-ray quiet binary with a black hole, VFTS 243, in the Large Magellanic Cloud. Assuming an isotropic, Maxwellian distribution on natal kicks and using broad agnostic mass priors, we find that kick velocity can be constrained to V k < 72 km s-1 at 90% confidence. We find that a Blaauw kick cannot be ruled out, and that at least about 0.6M ⊙ was lost during the supernova with 90% confidence. The pre-SN orbital separation is found to be robustly constrained to be around 0.3 au.

Keywords: black holes; bayesian statistics; astrophysical black holes; binary stars
Magnetic Helicity Signature and Its Role in Regulating Magnetic Energy Spectra and Proton Temperatures in the Solar Wind

In a previous paper, we found that perpendicular and parallel proton temperatures are clearly associated with the proton-scale turbulence in the solar wind, and magnetic helicity signature appears to be an important indicator in the association. Based on 15 yr of in situ measurements, the present paper further investigates the magnetic helicity of solar wind turbulence and its role in regulating magnetic energy spectra and proton temperatures. Results show that the presence of the helicity signature is very common in solar wind turbulence at scales $0.3\lesssim k{\rho }_{p}\lesssim 1$ , with k being the wavenumber and ρp the proton gyroradius. The sign of the helicity is mostly positive, indicating the dominance of right-handed polarization of the turbulence. The helicity magnitude usually increases with k and ${\beta }_{\parallel p}$ (the proton parallel beta) when $k{\rho }_{p}$ and ${\beta }_{\parallel p}$ are less than unity. As helicity magnitude increases, the power index of the energy spectrum becomes more negative, and the proton temperatures ${T}_{\perp p}$ and ${T}_{\parallel p}$ rise significantly, where ${T}_{\perp p}$ and ${T}_{\parallel p}$ are the perpendicular and parallel temperatures with respect to the background magnetic field. In particular, the rise of ${T}_{\perp p}$ is faster than ${T}_{\parallel p}$ when ${\beta }_{\parallel p}\lt 1$ is satisfied. The faster rise of ${T}_{\perp p}$ with the helicity magnitude may be interpreted as the result of the preferentially perpendicular heating of solar wind protons by kinetic Alfvén wave turbulence.

Keywords: solar wind; interplanetary turbulence; solar coronal heating; space plasmas; plasma physics
Variations in the Width, Density, and Direction of the Palomar 5 Tidal Tails

Stars that escape globular clusters form tidal tails that are predominantly shaped by the global distribution of mass in the Galaxy, but also preserve a historical record of small-scale perturbations. Using deep grz photometry from DECaLS, we present highly probable members of the tidal tails associated with the evaporating globular cluster Palomar 5. These data yield the cleanest view of a stellar stream beyond ≈20 kpc and reveal: (1) a wide, low surface-brightness extension of the leading tail; (2) significant density variations along the stream; and (3) sharp changes in the direction of both the leading and the trailing tail. In the fiducial Milky Way model, a rotating bar perturbs the Palomar 5 tails and can produce streams with similar width and density profiles to those observed. However, the deviations of the stream track in this simple model do not match those observed in the Palomar 5 trailing tail, indicating the need for an additional source of perturbation. These discoveries open up the possibility of measuring the population of perturbers in the Milky Way, including dark-matter subhalos, with an ensemble of stellar streams and deep photometry alone.

Keywords: globular star clusters; milky way dynamics; milky way stellar halo; milky way dark matter halo; tidal tails
New Spectroscopic Redshift Places PEARLSDG in a Group at ∼124 Mpc

PEARLSDG was previously reported as an isolated dwarf galaxy with a TRGB distance of 30 Mpc. New data show this to not be the case. We report a new spectroscopic redshift of 0.02809, which argues for an association with a group of galaxies at ∼124 Mpc.

Keywords: low surface brightness galaxies; james webb space telescope; dwarf galaxies; galaxy stellar content; stellar populations; galaxy evolution
Solar Energetic Particles Produced during Two Fast Coronal Mass Ejections

Two recent extremely fast coronal mass ejections (CMEs) are of particular interest. The first one originated from the southern hemisphere on 2021 October 28 and caused strong solar energetic particle (SEP) events over a wide longitude range from Earth, STEREO-A, to Mars. However, the other one, originating from the center of the Earth-viewed solar disk 5 days later, left weak SEP signatures in the heliosphere. Based on the white-light images of the CMEs from the Solar and Heliospheric Observatory (SOHO) and the Ahead Solar Terrestrial Relations Observatory (STEREO-A), in combination with the observations of the corresponding solar flares, radio bursts, and in situ magnetic fields and particles, we try to analyze the series of solar eruptions during October 28-November 2 as well as their correspondences with the in situ features. It is found that the difference in SEP features between the two CMEs is mainly due to (1) the seed particles probably supplied by associated flares and (2) the magnetic connection influenced by the preceding solar wind speed.

Keywords: solar coronal mass ejections; solar energetic particles; solar flares
Fast Generation of Mock Galaxy Catalogs with COLA

We investigate the feasibility of using the comoving Lagrangian acceleration (COLA) technique to efficiently generate galaxy mock catalogs that can accurately reproduce the statistical properties of observed galaxies. Our proposed scheme combines the subhalo abundance-matching (SHAM) procedure with COLA simulations, using only three free parameters: the scatter magnitude (σ scat) in SHAM, the initial redshift (z init) of the COLA simulation, and the time stride (da) used by COLA. In this proof-of-concept study, we focus on a subset of BOSS CMASS NGC galaxies within the redshift range z ∈ [0.45, 0.55]. We perform GADGET simulation and low-resolution COLA simulations with various combinations of (z init, da), each using 10243 particles in an 800 h ‑1 Mpc box. By minimizing the difference between COLA mock and CMASS NGC galaxies for the monopole of the two-point correlation function (2PCF), we obtain the optimal σ scat. We have found that by setting z init = 29 and da = 1/30, we achieve a good agreement between COLA mock and CMASS NGC galaxies within the range of 4–20 h ‑1 Mpc, with a computational cost lower by 2 orders of magnitude than that of the GADGET N-body code. Moreover, a detailed verification is performed by comparing various statistical properties, such as anisotropic 2PCF, three-point clustering, and power spectrum multipoles, which shows a similar performance of the GADGET mock and COLA mock catalogs with the CMASS NGC galaxies. Furthermore, we assess the robustness of the COLA mock catalogs for different cosmological models, demonstrating consistent results in the resulting 2PCFs. Our findings suggest that COLA simulations are a promising tool for efficiently generating mock catalogs for emulators and machine-learning analyses to explore the large-scale structure of the Universe.

Keywords: large-scale structure of the universe; galaxy dark matter halos; cosmology; n-body simulations
Mars Upper Atmospheric Temperature and Atomic Oxygen Density Derived from the O I 130.4 nm Emission Observed by NASA's MAVEN Mission

The abundance of atomic oxygen is a major unknown for the Mars upper atmosphere, and systematic measurements of this key species is a primary objective of NASA's Mars Atmosphere and Volatile Evolution (MAVEN) mission. Moreover, the Martian dayside temperature structure and its variability has been a subject of considerable debate in the past. In this study, an inversion analysis of the periapsis limb scans of the O I 130.4 nm emission observed by MAVEN is performed to quantify the neutral temperature and atomic oxygen abundance in the Mars upper atmosphere. Our analysis yields unprecedented resolution of the spatial variation of Mars atomic oxygen, showing that its exobase density decreases with the solar zenith angle (SZA) from ∼0° to 60° by about an order of magnitude, from ∼108 to ∼107 cm-3 near perihelion (2015 April) and from ∼107 to ∼106 cm-3 near aphelion (2017 November). For a given SZA the exobase densities near perihelion are about an order of magnitude higher than those near aphelion. The [O]/[CO2] mixing ratio at 130 km altitude can vary from ∼0.1% to 4.6%, which also decreases with increasing SZA. Moreover, it is shown that the Mars exobase temperature does not vary significantly with SZA from ∼0° to ∼60°, which is estimated to be ∼239.2 ± 27.6 K near perihelion and ∼162.4 ± 19.9 K near aphelion, with a difference of 76.8 K between these two seasonal extremes.

Keywords: mars; atmospheric composition; aeronomy
Temporal and Spectral Evolution of Gamma-Ray Burst Broad Pulses: Identification of High-latitude Emission in the Prompt Emission

We perform a detailed analysis of broad pulses in bright gamma-ray bursts (GRBs) to understand the evolution of GRB broad pulses. Using the temporal and spectral properties, we test the high-latitude emission (HLE) scenario in the decaying phase of broad pulses. The HLE originates from the curvature effect of a relativistic spherical jet, where higher-latitude photons are delayed and softer than the observer's line-of-sight emission. The signature of HLE has not yet been identified undisputedly during the prompt emission of GRBs. The HLE theory predicts a specific relation, ${F}_{\nu ,{E}_{p}}$ ∝ ${E}_{p}^{2}$ , between the peak energy E p in ν F ν spectra and the spectral flux F ν measured at E p , ${F}_{\nu ,{E}_{p}}$ . We search for evidence of this relation in 2157 GRBs detected by the Gamma-ray Burst Monitor on board the Fermi Gamma-ray Space Telescope from 2008 to 2017. After imposing unbiased selection criteria in order to minimize contamination in a signal by background and overlaps of pulses, we build a sample of 32 broad pulses in 32 GRBs. We perform a time-resolved spectral analysis on each of these 32 broad pulses and find that the evolution of 18 pulses (56%) is clearly consistent with the HLE relation. For the 18 broad pulses, the exponent δ in the relation of ${F}_{\nu ,{E}_{p}}$ ∝ E p δ is distributed as a Gaussian function with a median and width of 1.99 and 0.34, respectively. This result provides a constraint on the emission radius of GRBs with the HLE signature.

Keywords: gamma-ray bursts; relativistic jets
Titan Stratospheric Haze Bands Observed in Cassini VIMS as Tracers of Meridional Circulation

We analyzed Cassini data to derive the nature and evolution of circumglobal annuli observed in the stratosphere of Titan, Saturn's largest moon. The annuli were observed between 2004 and 2017 in data acquired by the Visual and Infrared Mapping Spectrometer on board the Cassini spacecraft. We observed a north polar annulus, an equatorial annulus, and several secondary annuli. Pre-Cassini telescopic observations by the Hubble Space Telescope and Keck reported an atmospheric feature consistent with the presence of a south polar annulus between 1999 and 2001, although this feature was not observed by Cassini. Relative to the atmosphere near the annuli, they appear dark at 300-500 nm and bright in methane absorption channels such as the ones at 900 and 1150 nm. The stratosphere seems to rotate around the north pole. Alternatively, it seems to rotate about a point offset from solid-body rotation axis by a few degrees; this point in turn rotates around the solid-body rotation axis.

Keywords: stratosphere; titan; atmospheric circulation; spectrophotometry; seasonal phenomena
Time-domain Study of the Young Massive Cluster Westerlund 2 with the Hubble Space Telescope. I

Time-domain studies of pre-main-sequence (PMS) stars have long been used to investigate star properties during their early evolutionary phases and to trace the evolution of circumstellar environments. Historically these studies have been confined to the nearest, low-density, star-forming regions. We used the Wide Field Camera 3 on board the Hubble Space Telescope to extend, for the first time, the study of PMS variability to one of the few young massive clusters in the Milky Way, Westerlund 2. Our analysis reveals that at least one-third of the intermediate- and low-mass PMS stars in Westerlund 2 are variable. Based on the characteristics of their light curves, we classified ∼11% of the variable stars as weak-line T Tauri candidates, ∼52% as classical T Tauri candidates, ∼5% as dippers, and ∼26% as bursters. In addition, we found that 2% of the stars below 6 M⊙ (∼6% of the variables) are eclipsing binaries, with orbital periods shorter than 80 days. The spatial distribution of the different populations of variable PMS stars suggests that stellar feedback and UV radiation from massive stars play an important role in the evolution of circumstellar and planetary disks.

Keywords: pre-main sequence stars; star formation; star forming regions; t tauri stars; weak-line t tauri stars; eclipsing binary stars; variable stars; young star clusters
CNO Cycle Burning in Ultra-low Metallicity Solar Mass Stars

We use the 1D stellar evolution code MESA to run select models at one solar mass at near zero metallicity to examine the effect of a lack of catalysts for CNO burning on the evolution of these models. We find that for metallicities below 10-10 ${Z}_{\odot }$ a loop occurs on the HR diagram as the star evolves off the main sequence, corresponding to the onset of significant CNO burning in the core of the star. This feature is visible in the Kippenhahn diagram as a period where the core becomes convective while the burning takes place. During this loop, the degeneracy of the core is lifted as CNO burning produces around 3.7% of the total nuclear energy.

Keywords: metallicity; stellar evolutionary models; carbon-nitrogen cycle
Volatile-rich Asteroids in the Inner Solar System

Bennu (101195), target of the Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer (OSIRIS-REx) mission, is a type-B asteroid with abundant spectral evidence for hydrated silicates, low thermal inertia "boulders" and frequent bursts of particle emission. We suggest that Bennu's parent body formed in the outer solar system before it was perturbed into the asteroid belt and then evolved into a near-Earth object. We show that this is consistent with models of planetesimal evolution. Bennu has many characteristics expected for a dormant comet, and could potentially contain a minimum of 1 wt.% adsorbed water if its gross mineralogy is consistent with the Orgueil meteorite. This is in addition to any ice or water contained within the hydrous minerals themselves. Based on this hypothesis, we predict the properties of the samples that will be returned to Earth by the OSIRIS-REx mission, including abundant phyllosilicate minerals, amorphous hydrated silicates and low-density, very high-porosity aggregates, already observed by the OSIRIS-REx instrument suite. We predict enrichments in D/H and 15N/14N, high C/Mg ratios (>∼7 wt%), and a greater range of organic compositions than found in meteorites, including an organic component poor in aromatics, and a more labile organic fraction. Ammonium salts, ranging from NH4Cl to ammonium-organic acid salts could carry much of the nitrogen in comets, yet only NH4CH3COO and heavier salts are sufficiently stable to be found in these returned samples. Water adsorbed onto highly porous grains should also be detected provided that the sample return capsule remains below 300 K during Earth return, and this water should be isotopically heavy.

Keywords: near-earth objects; meteorites; main-belt comets
Leave No Low-mass Star Behind: Results from Extended Surveys of Hα Emission from Stars in Praesepe and the Hyades

We present the results of our spectroscopic surveys of members of two nearby, rich open clusters, Praesepe and the Hyades, which fold in updated membership catalogs for both based on Gaia data. Our data include 1200 of our own R ≈ 2000 spectra (900 for Praesepe, 300 for the Hyades), 300 archival spectra (270 for Praesepe, 30 for the Hyades), and more than 1000 spectra obtained by the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (750 for Praesepe and 440 for the Hyades). For each good-quality spectrum, we measure the Hα equivalent width and run a Monte Carlo iterator to estimate the uncertainty. Our surveys include at least one spectrum for 870 stars in Praesepe and for 460 stars in the Hyades. The vast majority of these are stars later than F7 (<1.2 M⊙). Our coverage extends down to a spectral type of M6 (≈0.2 M⊙) in both clusters, allowing us to compare in detail the equivalent-width distributions for these two coeval populations (≈800 Myr). Our surveys represent the most extensive investigations of Hα emission in single-aged low-mass stellar populations to date, and form the basis of our exploration of the age-rotation-activity in these two benchmark clusters. * This work is based on observations obtained at the MDM Observatory, operated by Dartmouth College, Columbia University, Ohio State University, Ohio University, and the University of Michigan.

Keywords: open star clusters; low mass stars; stellar activity; surveys
The Nature of the Eccentric Double-lined Eclipsing Binary System KIC 2306740 with Kepler Space Photometry

We present a detailed study of KIC 2306740, an eccentric double-lined eclipsing binary system. Kepler satellite data were combined with spectroscopic data obtained with the 4.2 m William Herschel Telescope (WHT). This allowed us to determine precise orbital and physical parameters of this relatively long period (P = 10.3°) and slightly eccentric (e = 0.3) binary system. The physical parameters have been determined to be M1 = 1.194 ± 0.008 M⊙, M2 = 1.078 ± 0.007 M⊙, R1 = 1.682 ± 0.004 R⊙, R2 = 1.226 ± 0.005 R⊙, L1 = 2.8 ± 0.4 L⊙, L2 = 1.8 ± 0.2 L⊙, and orbital separation a = 26.20 ± 0.04 R⊙ through simultaneous solutions of the Kepler light curves and WHT radial velocity data. Binarity effects were extracted from the light curve in order to study intrinsic variations in the residuals. Five significant and more than 100 combination frequencies were detected. We modeled the binary system assuming nonconservative evolution models with the Cambridge STARS (TWIN) code, and we show the evolutionary tracks of the components in the $\mathrm{log}L\mbox{--}\mathrm{log}T$ plane, the $\mathrm{log}R\mbox{--}\mathrm{log}M$ plane, and the $\mathrm{log}P\mbox{--}\mathrm{age}$ plane for both spin and orbital periods together with eccentricity e and $\mathrm{log}{R}_{1}$ . The model of the nonconservative processes in the code led the system to evolve to the observed system parameters in roughly 5.1 Gyr.

Keywords: detached binary stars; binary stars; eclipsing binary stars
Machine Learning the Sixth Dimension: Stellar Radial Velocities from 5D Phase-space Correlations

The Gaia satellite will observe the positions and velocities of over a billion Milky Way stars. In the early data releases, the majority of observed stars do not have complete 6D phase-space information. In this Letter, we demonstrate the ability to infer the missing line-of-sight velocities until more spectroscopic observations become available. We utilize a novel neural network architecture that, after being trained on a subset of data with complete phase-space information, takes in a star's 5D astrometry (angular coordinates, proper motions, and parallax) and outputs a predicted line-of-sight velocity with an associated uncertainty. Working with a mock Gaia catalog, we show that the network can successfully recover the distributions and correlations of each velocity component for stars that fall within ~5 kpc of the Sun. We also demonstrate that the network can accurately reconstruct the velocity distribution of a kinematic substructure in the stellar halo that is spatially uniform, even when it comprises a small fraction of the total star count.

Keywords: radial velocity; neural networks; dark matter; milky way dynamics