adsabs/SciX_UAT_keywords huggingface dataset:
The Limited Role of the Streaming Instability during Moon and Exomoon Formation

It is generally accepted that the Moon accreted from the disk formed by an impact between the proto-Earth and impactor, but its details are highly debated. Some models suggest that a Mars-sized impactor formed a silicate melt-rich (vapor-poor) disk around Earth, whereas other models suggest that a highly energetic impact produced a silicate vapor-rich disk. Such a vapor-rich disk, however, may not be suitable for the Moon formation, because moonlets, building blocks of the Moon, of 100 m–100 km in radius may experience strong gas drag and fall onto Earth on a short timescale, failing to grow further. This problem may be avoided if large moonlets (≫100 km) form very quickly by streaming instability, which is a process to concentrate particles enough to cause gravitational collapse and rapid formation of planetesimals or moonlets. Here, we investigate the effect of the streaming instability in the Moon-forming disk for the first time and find that this instability can quickly form ∼100 km-sized moonlets. However, these moonlets are not large enough to avoid strong drag, and they still fall onto Earth quickly. This suggests that the vapor-rich disks may not form the large Moon, and therefore the models that produce vapor-poor disks are supported. This result is applicable to general impact-induced moon-forming disks, supporting the previous suggestion that small planets (<1.6 R ⊕) are good candidates to host large moons because their impact-induced disks would likely be vapor-poor. We find a limited role of streaming instability in satellite formation in an impact-induced disk, whereas it plays a key role during planet formation.

Keywords: earth-moon system
Geometric Assumptions in Hydrodynamic Modeling of Coronal and Flaring Loops

In coronal loop modeling, it is commonly assumed that the loops are semicircular with a uniform cross-sectional area. However, observed loops are rarely semicircular, and extrapolations of the magnetic field show that the field strength decreases with height, implying that the cross-sectional area expands with height. We examine these two assumptions directly, to understand how they affect the hydrodynamic and radiative response of short, hot loops to strong, impulsive electron beam heating events. Both the magnitude and rate of area expansion impact the dynamics directly, and an expanding cross section significantly lengthens the time for a loop to cool and drain, increases upflow durations, and suppresses sound waves. The standard T ~ n 2 relation for radiative cooling does not hold with expanding loops, which cool with relatively little draining. An increase in the eccentricity of loops, on the other hand, only increases the draining timescale, and is a minor effect in general. Spectral line intensities are also strongly impacted by the variation in the cross-sectional area because they depend on both the volume of the emitting region as well as the density and ionization state. With a larger expansion, the density is reduced, so the lines at all heights are relatively reduced in intensity, and because of the increase of cooling times, the hottest lines remain bright for significantly longer. Area expansion is critical to accurate modeling of the hydrodynamics and radiation, and observations are needed to constrain the magnitude, rate, and location of the expansion-or lack thereof.

Keywords: solar spectral irradiance; solar physics; hydrodynamics; hydrodynamical simulations; solar flare spectra; solar flares; solar coronal loops
VVV Survey Microlensing: The Galactic Latitude Dependence

We search for microlensing events in fields along the Galactic minor axis, ranging from the Galactic center to -3°7 < b < 3°9 using the VISTA Variables in the Via Láctea (VVV) survey near-IR photometry. The new search is made across VVV tiles b291, b305, b319, b347, b361, and b375, covering a total area of about 11.5 deg2. We find a total of N = 238 new microlensing events in this new area, N = 74, which are classified as bulge red clump (RC) giant sources. Combining them with N = 122 events that we had previously reported in the Galactic center (VVV tile b333), allows us to study the latitude distribution of the microlensing events reaching the Galactic plane at b = 00 for the first time. We find a very strong dependence of the number of microlensing events with Galactic latitude, a number that increases rapidly toward the Galactic center by one order of magnitude from $| b| =2$ ° to b = 0° with a much steeper gradient than with Galactic longitude. The microlensing event population shows a flattened distribution (axial ratio b/a ≈ 1.5). The final sample shows a shorter mean timescale distribution than the Galactic plane sample for both the complete population and RC stars.

Keywords: galactic bulge; milky way galaxy physics; galaxy structure; gravitational microlensing; gravitational lensing; galactic center
New Investigations of Dark-floored Pits In the Volatile Ice of Sputnik Planitia on Pluto

Sputnik Planitia, Pluto's gigantic, volatile ice glacier, hosts numerous scientific mysteries, including the presence of thousands of elongated pit structures. We examine various attributes of these pit structures in New Horizons data sets, revealing their length, aspect ratio, and orientation properties; we also study their reflectivities, colors, and compositions, and compare these attributes to some other relevant regions on Pluto. We then comment on origin mechanisms of the pits and also the fate of the missing volatiles represented by the pits on Sputnik Planitia. From a sample of 317 pits, we find typical length/width ratios of 2-4, with their major axis preferentially oriented approximately north-south. We also find that the floors of large pits in our sample have similar single-scattering albedos and colors to dark material on crater rims and floors (i.e., possible subsurface windows) in Burney basin. We also find that the base of the three pits in our sample, large enough to study with LEISA IR spectroscopy, display both CH4 and N2 absorption features, as do the dark regions in crater windows in Burney basin. Evidence for a sublimation erosion origin for the pits is supported over both the explosion/ejecta venting and structural collapse alternatives. Finally, we find that the mass lost by the pits on Sputnik Planitia most likely lies condensed elsewhere, on Pluto's surface, relocated there by volatile transport as opposed to removal by escape to space or photochemical conversion.

Keywords: pluto; atmospheric effects; surface processes; surface ices
Inferring More from Less: Prospector as a Photometric Redshift Engine in the Era of JWST

The advent of the James Webb Space Telescope (JWST) signals a new era in exploring galaxies in the high-z universe. Current and upcoming JWST imaging will potentially detect galaxies at z ~ 20, creating a new urgency in the quest to infer accurate photometric redshifts (photo-z) for individual galaxies from their spectral energy distributions, as well as masses, ages, and star formation rates. Here we illustrate the utility of informed priors encoding previous observations of galaxies across cosmic time in achieving these goals. We construct three joint priors encoding empirical constraints of redshifts, masses, and star formation histories in the galaxy population within the Prospector Bayesian inference framework. In contrast with uniform priors, our model breaks an age-mass-redshift degeneracy, and thus reduces the mean bias error in masses from 0.3 to 0.1 dex, and in ages from 0.6 to 0.2 dex in tests done on mock JWST observations. Notably, our model recovers redshifts at least as accurately as the state-of-the-art photo-z code EAzY in deep JWST fields, but with two advantages: tailoring a model based on a particular survey is rendered mostly unnecessary given well-motivated priors; obtaining joint posteriors describing stellar, active galactic nuclei, gas, and dust contributions becomes possible. We can now confidently use the joint distribution to propagate full non-Gaussian redshift uncertainties into inferred properties of the galaxy population. This model, "Prospector-β," is intended for fitting galaxy photometry where the redshift is unknown, and will be instrumental in ensuring the maximum science return from forthcoming photometric surveys with JWST. The code is made publicly available online as a part of Prospector 9 9 The version used in this work corresponds to the state of the Git repository at commit https://github.com/bd-j/prospector/commit/820ad72363a1f9c22cf03610bfe6e361213385cd..

Keywords: bayesian statistics; computational astronomy; galaxy evolution; galaxy formation; redshift surveys; spectrophotometry; spectral energy distribution
HD 222925: A New Opportunity to Explore the Astrophysical and Nuclear Conditions of r-process Sites

With the most trans-iron elements detected of any star outside the solar system, HD 222925 represents the most complete chemical inventory among metal-poor stars enhanced with elements made by the rapid neutron capture ("r") process. As such, HD 222925 may be a new "template" for the observational r-process, where before the (much higher-metallicity) solar r-process residuals were used. In this work, we test under which conditions a single site accounts for the entire elemental r-process abundance pattern of HD 222925. We found that several of our tests-with the single exception of the black hole-neutron star merger case-challenge the single-site assumption by producing an ejecta distribution that is highly constrained, in disagreement with simulation predictions. However, we found that ejecta distributions that are more in line with simulations can be obtained under the condition that the nuclear data near the second r-process peak are changed. Therefore, for HD 222925 to be a canonical r-process template likely as a product of a single astrophysical source, the nuclear data need to be reevaluated. The new elemental abundance pattern of HD 222925-including the abundances obtained from space-based, ultraviolet (UV) data-call for a deeper understanding of both astrophysical r-process sites and nuclear data. Similar UV observations of additional r-process-enhanced stars will be required to determine whether the elemental abundance pattern of HD 222925 is indeed a canonical template (or an outlier) for the r-process at low metallicity.

Keywords: nucleosynthesis; nuclear astrophysics; r-process; population ii stars; nuclear physics
Spherical Harmonic Representation of Energetic Neutral Atom Flux Components Observed by IBEX

The Interstellar Boundary Explorer (IBEX) images the heliosphere by observing energetic neutral atoms (ENAs). The IBEX-Hi instrument on board IBEX provides full-sky maps of ENA fluxes produced in the heliosphere and very local interstellar medium through charge exchange of suprathermal ions with interstellar neutral atoms. The first IBEX-Hi results showed that, in addition to the anticipated globally distributed flux (GDF), a narrow and bright emission from a circular region in the sky, dubbed the IBEX ribbon, is visible in all energy steps. While the GDF is mainly produced in the inner heliosheath, ample evidence indicates that the ribbon forms outside the heliopause in the regions where the interstellar magnetic field is perpendicular to the lines of sight. The IBEX maps produced by the mission team distribute the observations into 6° × 6° rectangle pixels in ecliptic coordinates. The overlap of the GDF and ribbon components complicates qualitative analyses of each source. Here, we find the spherical harmonic representation of the IBEX maps, separating the GDF and ribbon components. This representation describes the ENA flux components in the sky without relying on any pixelization scheme. Using this separation, we discuss the temporal evolution of each component over the solar cycle. We find that the GDF is characterized by larger spatial scale structures than those of the ribbon. However, we identify two isolated, small-scale signals in the GDF region that require further study.

Keywords: heliosphere; heliosheath; interstellar medium wind; heliopause; solar wind; solar cycle; space plasmas
A First Look at Cepheids in a Type Ia Supernova Host with JWST

We report the first look at extragalactic Cepheid variables with the James Webb Space Telescope (JWST), obtained from an archival observation of NGC 1365, host of SNIa 2012fr, a calibration path used to measure the Hubble constant. As expected, the high-resolution observations with NIRCam through F200W show better source separation from line-of-sight companions than Hubble Space Telescope (HST) images at similar near-infrared wavelengths, the spectral region that has been used to mitigate the impact of host dust on distance measurements. Using the standard star P330E as a zero-point and point-spread function reference, we photometered 31 previously known Cepheids in the JWST field, spanning $1.15\lt \mathrm{log}P\lt 1.75$ including 24 Cepheids in the longer-period interval of $1.35\lt \mathrm{log}P\lt 1.75$ . We compared the resultant period-luminosity (P-L) relations to that of 49 Cepheids in the full period range including 38 in the longer-period range observed with WFC3/IR on HST and transformed to the JWST photometric system (F200W, Vega). The P-L relations measured are in good agreement, with intercepts (at $\mathrm{log}P=1$ ) of 25.74 ± 0.04 and 25.72 ± 0.05 for HST and JWST, respectively. Our baseline result comes from the longer-period, higher signal-to-noise ratio Cepheids where we find 25.75 ± 0.05 and 25.75 ± 0.06 mag for HST and JWST, respectively. We find good consistency between this first JWST measurement and HST, and no evidence that HST Cepheid photometry is "biased bright" at the ~0.2 mag level needed to mitigate the Hubble tension, though comparisons from more SN hosts are warranted and anticipated. We expect future optimized JWST observations to surpass these in quality.

Keywords: hubble constant; james webb space telescope; cepheid distance; cepheid variable stars
Inpainting Galactic Foreground Intensity and Polarization Maps Using Convolutional Neural Networks

The Deep Convolutional Neural Networks (DCNNs) have been a popular tool for image generation and restoration. In this work, we applied DCNNs to the problem of inpainting non-Gaussian astrophysical signal, in the context of Galactic diffuse emissions at the millimetric and submillimetric regimes, specifically Synchrotron and Thermal Dust emissions. Both signals are affected by contamination at small angular scales due to extragalactic radio sources (the former) and dusty star-forming galaxies (the latter). We compare the performance of the standard diffusive inpainting with that of two novel methodologies relying on DCNNs, namely Generative Adversarial Networks and Deep-Prior. We show that the methods based on the DCNNs are able to reproduce the statistical properties of the ground-truth signal more consistently with a higher confidence level. The Python Inpainter for Cosmological and AStrophysical SOurces (PICASSO) is a package encoding a suite of inpainting methods described in this work and has been made publicly available at http://giuspugl.github.io/picasso/.

Keywords: cosmic microwave background radiation; extragalactic radio sources; convolutional neural networks; interstellar synchrotron emission; dust continuum emission
Uncovering Magnetic Turbulence in Young Supernova Remnants with Polarized X-Ray Imaging

Observations of young supernova remnants (SNRs) in X-rays and γ-rays have provided conclusive evidence for particle acceleration to at least TeV energies. Analysis of high-spatial-resolution X-ray maps of young SNRs has indicated that the particle acceleration process is accompanied by strong nonadiabatic amplification of magnetic fields. If Fermi acceleration is the mechanism producing the energetic cosmic rays (CRs), the amplified magnetic field must be turbulent, and CR-driven instabilities are among the most probable mechanisms for converting the shock ram pressure into magnetic turbulence. The development and evolution of strong magnetic turbulence in collisionless plasmas forming SNR shells are complicated phenomena which include the amplification of magnetic modes, anisotropic mode transformations at shocks, as well as the nonlinear physics of turbulent cascades. Polarized X-ray synchrotron radiation from ultrarelativistic electrons accelerated in the SNR shock is produced in a thin layer immediately behind the shock and is not subject to the Faraday depolarization effect. These factors open up possibilities to study some properties of magnetic turbulence, and here we present polarized X-ray synchrotron maps of SNR shells assuming different models of magnetic turbulence cascades. It is shown that different models of anisotropic turbulence can be distinguished by measuring the predominant polarization angle direction. We discuss the detection of these features in Tycho's SNR with the coming generation of X-ray polarimeters such as the Imaging X-ray Polarimetry Explorer.

Keywords: shocks; particle astrophysics; cosmic rays; high energy astrophysics; supernova remnants; plasma astrophysics; space plasmas; interstellar synchrotron emission; starlight polarization
The Properties and Origin of Kuiper Belt Object Arrokoth's Large Mounds

We report on a study of the mounds that dominate the appearance of Kuiper Belt Object (486958) Arrokoth's larger lobe, named Wenu. We compare the geological context of these mounds and measure and intercompare their shapes, sizes/orientations, reflectance, and colors. We find the mounds are broadly self-similar in many respects and interpret them as the original building blocks of Arrokoth. It remains unclear why these building blocks are so similar in size-and this represents a new constraint and challenge for solar system formation models. We then discuss the implications of this interpretation.

Keywords: kuiper belt; classical kuiper belt objects; trans-neptunian objects; planetesimals; accretion
Flares, Rotation, Activity Cycles, and a Magnetic Star-Planet Interaction Hypothesis for the Far-ultraviolet Emission of GJ 436

Variability in the far-ultraviolet (FUV) emission produced by stellar activity affects photochemistry and heating in orbiting planetary atmospheres. We present a comprehensive analysis of the FUV variability of GJ 436, a field-age M2.5V star (P rot ≈ 44 days) that is orbited by a warm Neptune-sized planet (M ≈ 25 M ⊕, R ≈ 4.1 M ⊕, P orb ≈ 2.6 days). Observations at three epochs from 2012 to 2018 span nearly a full activity cycle, sample two rotations of the star and two orbital periods of the planet, and reveal a multitude of brief flares. From 2012 to 2018, the star's 7.75 ± 0.10 yr activity cycle produced the largest observed variations, 38% ± 3% in the summed flux of the major FUV emission lines. In 2018, the variability due to rotation was 8% ± 2%. An additional 11% ± 1% scatter at a cadence of 10 minutes, which is treated as white noise in the fits, likely has both instrumental and astrophysical origins. Flares increased time-averaged emission by 15% over the 0.88 days of cumulative exposure, peaking as high as 25× quiescence. We interpret these flare values as lower limits given that flares too weak or too infrequent to have been observed likely exist. GJ 436's flare frequency distribution at FUV wavelengths is unusual compared to other field-age M dwarfs, exhibiting a statistically significant dearth of high-energy (>4 × 1028 erg) events, which we hypothesize to be the result of a magnetic star-planet interaction (SPI) triggering premature flares. If an SPI is present, GJ 436 b's magnetic field strength must be ≲100 G to explain the statistically insignificant increase in the orbit-phased FUV emission.

Keywords: stellar activity; exoplanets; magnetic fields; late-type dwarf stars; ultraviolet astronomy; m dwarf stars; star-planet interactions; stellar rotation; stellar flares
Thermal Pressures in the Interstellar Medium away from Stellar Environments

Interstellar thermal pressures can be measured using C I absorption lines that probe the pressure-sensitive populations of the fine-structure levels of its ground state. In a survey of C I absorption toward Galactic hot stars, Jenkins & Tripp found evidence of small amounts (~0.05&percnt;) of gas at high pressures ( $p/k\gg {10}^{4}\,{\mathrm{cm}}^{-3}\,{\rm{K}}$ ) mixed with a more general presence of lower pressure material exhibiting a log-normal distribution that spanned the range ${10}^{3}\lesssim p/k\lesssim {10}^{4}\,{\mathrm{cm}}^{-3}\,{\rm{K}}$ . In this paper, we study Milky Way C I lines in the spectra of extragalactic sources instead of Galactic stars and thus measure the pressures without being influenced by regions where stellar mass loss and H II region expansions could create localized pressure elevations. We find that the distribution of low pressures in the current sample favors slightly higher pressures than the earlier survey, and the fraction of gaseous material at extremely high pressures is about the same as that found earlier. Thus we conclude that the earlier survey was not appreciably influenced by the stellar environments, and the small amounts of high pressure gas indeed exist within the general interstellar medium. * Based on observations with the NASA/ESA Hubble Space Telescope obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the Associations of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555.

Keywords: interstellar line absorption; diffuse interstellar clouds; cold neutral medium; ultraviolet astronomy; interstellar atomic gas
The Extraordinary Outburst in the Massive Protostellar System NGC 6334 I-MM1: Spatiokinematics of Water Masers during a Contemporaneous Flare Event

Following an eruptive accretion event in NGC 6334I-MM1, flares in the various maser species, including water masers, were triggered. We report the observed relative proper motion of the highly variable water masers associated with the massive star-forming region, NGC 6334I. High velocity H2O maser proper motions were detected in five maser clusters, CM2-W2 (bow-shock structure), MM1-W1, MM1-W3, UCHII-W1, and UCHII-W3. The overall average of the derived relative proper motion is 85 km s-1. This mean proper motion is in agreement with the previous results from VLA multiepoch observations. Our position as well as the velocity variance and covariance matrix analyses of the maser proper motions show its major axis to have a position angle of -79°4, cutting through the dust cavity around MM1B and being aligned in the northwest-southeast direction. We interpret this as the axis of the jet driving the CM2 shock and the maser motion. The complicated proper motions in MM1-W1 can be explained by the combined influence of the MM1 northeast-southwest bipolar outflow, the CS(6-5) north-south collimated bipolar outflow, and the radio jet. The relative proper motions of the H2O masers in UCHII-W1 are likely not driven by the jets of the MM1B protostar but by MM3-UCHII. Overall, the post-accretion burst relative proper motions of the H2O masers trace shocks of jet motion.

Keywords: stellar jets; astrophysical masers; long baseline interferometry; shocks