Sazuna/UAT_keywords huggingface dataset:
Water Ice Cloud Variability and Multi-epoch Transmission Spectra of TRAPPIST-1e. The precise characterization of terrestrial atmospheres with the James Webb Space Telescope (JWST) is one of the utmost goals of exoplanet astronomy in the next decade. With JWST's impending launch, it is crucial that we are well prepared to understand the subtleties of terrestrial atmospheres—particularly ones that we may have not needed to consider before due to instrumentation limitations. In this work we show that patchy ice cloud variability is present in the upper atmospheres of M-dwarf terrestrial planets, particularly along the limbs. Here we test whether these variable clouds will introduce unexpected biases in the multi-epoch observations necessary to constrain atmospheric abundances. Using 3D ExoCAM general circulation models of TRAPPIST-1e, we simulate five different climates with varying pCO2 to explore the strength of this variability. These models are post-processed using NASA Goddard's Planetary Spectrum Generator and PandExo to generate simulated observations with JWST's NIRSpec PRISM mode at 365 different temporal outputs from each climate. Assuming the need for 10 transits of TRAPPIST-1e to detect molecular features at great confidence, we then use CHIMERA to retrieve on several randomly selected weighted averages of our simulated observations to explore the effect of multi-epoch observations with variable cloud cover along the limb on retrieved abundances. We find that the variable spectra do not affect retrieved abundances at detectable levels for our sample of TRAPPIST-1e models.

Keywords: Exoplanet atmospheric composition , Exoplanet atmospheric variability, Exoplanet atmospheres, Atmospheric variability
Direct Multipoint Observations Capturing the Reformation of a Supercritical Fast Magnetosonic Shock. Using multipoint Magnetospheric Multiscale (MMS) observations in an unusual string-of-pearls configuration, we examine in detail observations of the reformation of a fast magnetosonic shock observed on the upstream edge of a foreshock transient structure upstream of Earth's bow shock. The four MMS spacecraft were separated by several hundred kilometers, comparable to suprathermal ion gyroradius scales or several ion inertial lengths. At least half of the shock reformation cycle was observed, with a new shock ramp rising up out of the "foot" region of the original shock ramp. Using the multipoint observations, we convert the observed time-series data into distance along the shock normal in the shock's rest frame. That conversion allows for a unique study of the relative spatial scales of the shock's various features, including the shock's growth rate, and how they evolve during the reformation cycle. Analysis indicates that the growth rate increases during reformation, electron-scale physics play an important role in the shock reformation, and energy conversion processes also undergo the same cyclical periodicity as reformation. Strong, thin electron-kinetic-scale current sheets and large-amplitude electrostatic and electromagnetic waves are reported. Results highlight the critical cross-scale coupling between electron-kinetic- and ion-kinetic-scale processes and details of the nature of nonstationarity, shock-front reformation at collisionless, fast magnetosonic shocks.

Keywords: Shocks, Planetary bow shocks
Velocity Dispersion of the GD-1 Stellar Stream. Tidally dissolved globular clusters form thin stellar streams that preserve a historical record of their past evolution. We report a radial velocity dispersion of 2.1 ± 0.3 km s-1 in the GD-1 stellar stream using a sample of 43 spectroscopically confirmed members. The GD-1 velocity dispersion is constant over the surveyed ≈15° span of the stream. We also measured velocity dispersion in the spur adjacent to the main GD-1 stream, and found a similar value at the tip of the spur. Surprisingly, the region of the spur closer to the stream appears dynamically colder than the main stream. An unperturbed model of the GD-1 stream has a velocity dispersion of ≈0.5 km s-1, indicating that GD-1 has undergone dynamical heating. Stellar streams arising from globular clusters, which prior to their arrival in the Milky Way, orbited a dwarf galaxy with a cored density profile are expected to have experienced the amount of heating required to match the velocity dispersion observed in GD-1. This suggests that GD-1 has been accreted and that imprints of its original host galaxy, including the inner slope of its dark matter halo, remain observable in the stream today.

Keywords: Cold dark matter, Galaxy dynamics, Milky Way dynamics, Stellar dynamics
Self-supervised Representation Learning for Astronomical Images. Sky surveys are the largest data generators in astronomy, making automated tools for extracting meaningful scientific information an absolute necessity. We show that, without the need for labels, self-supervised learning recovers representations of sky survey images that are semantically useful for a variety of scientific tasks. These representations can be directly used as features, or fine-tuned, to outperform supervised methods trained only on labeled data. We apply a contrastive learning framework on multiband galaxy photometry from the Sloan Digital Sky Survey (SDSS), to learn image representations. We then use them for galaxy morphology classification and fine-tune them for photometric redshift estimation, using labels from the Galaxy Zoo 2 data set and SDSS spectroscopy. In both downstream tasks, using the same learned representations, we outperform the supervised state-of-the-art results, and we show that our approach can achieve the accuracy of supervised models while using 2-4 times fewer labels for training. The codes, trained models, and data can be found at https://portal.nersc.gov/project/dasrepo/self-supervised-learning-sdss.

Keywords: Observational astronomy, Sky surveys, Observational cosmology, Computational methods, Astronomical methods
Astrophysics Milestones for Pulsar Timing Array Gravitational-wave Detection. The NANOGrav Collaboration reported strong Bayesian evidence for a common-spectrum stochastic process in its 12.5 yr pulsar timing array data set, with median characteristic strain amplitude at periods of a year of ${A}_{\mathrm{yr}}={1.92}_{-0.55}^{+0.75}\times {10}^{-15}$ . However, evidence for the quadrupolar Hellings &amp; Downs interpulsar correlations, which are characteristic of gravitational-wave signals, was not yet significant. We emulate and extend the NANOGrav data set, injecting a wide range of stochastic gravitational-wave background (GWB) signals that encompass a variety of amplitudes and spectral shapes, and quantify three key milestones. (I) Given the amplitude measured in the 12.5 yr analysis and assuming this signal is a GWB, we expect to accumulate robust evidence of an interpulsar-correlated GWB signal with 15-17 yr of data, i.e., an additional 2-5 yr from the 12.5 yr data set. (II) At the initial detection, we expect a fractional uncertainty of 40% on the power-law strain spectrum slope, which is sufficient to distinguish a GWB of supermassive black hole binary origin from some models predicting more exotic origins. (III) Similarly, the measured GWB amplitude will have an uncertainty of 44% upon initial detection, allowing us to arbitrate between some population models of supermassive black hole binaries. In addition, power-law models are distinguishable from those having low-frequency spectral turnovers once 20 yr of data are reached. Even though our study is based on the NANOGrav data, we also derive relations that allow for a generalization to other pulsar timing array data sets. Most notably, by combining the data of individual arrays into the International Pulsar Timing Array, all of these milestones can be reached significantly earlier.

Keywords: Pulsar timing method, Millisecond pulsars, Gravitational wave astronomy, Gravitational waves, Astronomical simulations
Time-series and Phase-curve Photometry of the Episodically Active Asteroid (6478) Gault in a Quiescent State Using APO, GROWTH, P200, and ZTF. We observed the episodically active asteroid (6478) Gault in 2020 with multiple telescopes in Asia and North America and found that it is no longer active after its recent outbursts at the end of 2018 and the start of 2019. The inactivity during this apparition allowed us to measure the absolute magnitude of Gault of Hr = 14.63 ± 0.02, Gr = 0.21 ± 0.02 from our secular phase-curve observations. In addition, we were able to constrain Gault's rotation period using time-series photometric lightcurves taken over 17 hr on multiple days in 2020 August, September, and October. The photometric lightcurves have a repeating ≲0.05 mag feature suggesting that (6478) Gault has a rotation period of ∼2.5 hr and may have a semispherical or top-like shape, much like the near-Earth asteroids Ryugu and Bennu. The rotation period of ∼2.5 hr is near the expected critical rotation period for an asteroid with the physical properties of (6478) Gault, suggesting that its activity observed over multiple epochs is due to surface mass shedding from its fast rotation spin-up by the Yarkovsky-O'Keefe-Radzievskii-Paddack effect.

Keywords: Main belt asteroids, Asteroids, Asteroid dynamics
Slowdown and Heating of Interstellar Neutral Helium by Elastic Collisions beyond the Heliopause. Direct sampling of interstellar neutral (ISN) atoms close to the Sun enables studies of the very local interstellar medium (VLISM) around the heliosphere. The primary population of ISN helium atoms has, until now, been assumed to reflect the pristine VLISM conditions at the heliopause. Consequently, the atoms observed at 1 au by the Interstellar Boundary Explorer (IBEX) were used to determine the VLISM temperature and velocity relative to the Sun, without accounting for elastic collisions with other species outside the heliopause. Here, we evaluate the effect of these collisions on the primary ISN helium population. We follow trajectories of helium atoms and track their collisions with slowed plasma and interstellar hydrogen atoms ahead of the heliopause. Atoms typically collide a few times in the outer heliosheath, and only ∼1.5% of the atoms are not scattered at all. We use calculated differential cross sections to randomly choose scattering angles in these collisions. We estimate that the resulting primary ISN helium atoms at the heliopause are slowed down by ∼0.45 km s-1 and heated by ∼1100 K compared to the pristine VLISM. The resulting velocity distribution is asymmetric and shows an extended tail in the antisunward direction. Accounting for this change in the parameters derived from IBEX observations gives the Sun's relative speed of 25.85 km s-1 and temperature of 6400 K in the pristine VLISM. Finally, this Letter serves as a source of the differential cross sections for elastic collisions with helium atoms.

Keywords: Heliopause, Heliosphere, Interstellar atomic gas, Interstellar abundances, Interstellar plasma, Collision physics, Interstellar medium, Heliosheath
Emerging Dimming as Coronal Heating Episodes. Emerging dimming occurs in isolated solar active regions (ARs) during the early stages of magnetic flux emergence. Observed by the Atmospheric Imaging Assembly, it features a rapid decrease in extreme-ultraviolet (EUV) emission in the 171 Å channel images, and a simultaneous increase in the 211 Å images. Here, we analyze the coronal thermodynamic and magnetic properties to probe its physical origin. We calculate the time-dependent differential emission measures for a sample of 18 events between 2010 and 2012. The emission measure (EM) decrease in the temperature range $5.7\leqslant {\mathrm{log}}_{10}T\leqslant 5.9$ is well correlated with the EM increase in $6.2\leqslant {\mathrm{log}}_{10}T\leqslant 6.4$ over eight orders of magnitude. This suggests that the coronal plasma is being heated from the quiet-Sun, sub-MK temperature to 1-2 MK, more typical for ARs. Potential field extrapolation indicates significant change in the local magnetic connectivity: the dimming region is now linked to the newly emerged flux via longer loops. We conclude that emerging dimming is likely caused by coronal heating episodes, powered by reconnection between the emerging and the ambient magnetic fields.

Keywords: Solar coronal heating, Solar magnetic flux emergence, Solar extreme ultraviolet emission
Revealing Gravitational Collapse in the Serpens G3-G6 Molecular Cloud Using Velocity Gradients. The relative role of turbulence, magnetic fields, and self-gravity in star formation is a subject of intensive debate. We present IRAM 30 m telescope observations of the 13CO (1-0) emission in the Serpens G3-G6 molecular cloud and apply to the data a set of statistical methods. These include the probability density functions of column density and the velocity gradients technique. We combine our data with the Planck 353 GHz polarized dust emission observations and Hershel H2 column density. We suggest that the Serpens G3-G6 south clump is undergoing a gravitational collapse. Our analysis reveals that the gravitational collapse happens at volume density n ≥ 103 cm-3. We estimate the plane-of-the-sky magnetic field strength to be approximately 120 μG using the traditional Davis-Chandrasekhar-Fermi method and 100 μG using a new technique proposed in Lazarian et al (2020). We find that the Serpens G3-G6 south clump's total magnetic field energy significantly surpasses kinetic energy and gravitational energy. We conclude that the gravitational collapse could be successfully triggered in a supersonic and sub-Alfvénic cloud.

Keywords: Interstellar magnetic fields, Star forming regions, Interstellar dynamics, Interstellar medium
Assessing the Formation of Solid Hydrogen Objects in Starless Molecular Cloud Cores. The properties of the first-discovered interstellar object (ISO), 1I/2017 ('Oumuamua), differ from both solar system asteroids and comets, casting doubt on a protoplanetary disk origin. In this study, we investigate the possibility that it formed with a substantial H2 ice component in the starless core of a giant molecular cloud. While interstellar solid hydrogen has yet to be detected, this constituent would explain a number of the ISO's properties. We consider the relevant processes required to build decameter-sized, solid hydrogen bodies and assess the plausibility of growth in various size regimes. Via an energy balance argument, we find the most severe barrier to formation is the extremely low temperature required for the favorability of molecular hydrogen ice. However, if deposition occurs, we find that the turbulence within starless cores is conducive for growth into kilometer-sized bodies on sufficiently short timescales. Then, we analyze mass loss in the interstellar medium and determine the necessary size for a hydrogen object to survive a journey to the solar system as a function of ISO age. Finally, we discuss the implications if the H2 explanation is correct, and we assess the future prospects of ISO science. If hydrogen ice ISOs do exist, our hypothesized formation pathway would require a small population of porous, 100 μm dust in a starless core region that has cooled to 2.8 K via adiabatic expansion of the surrounding gas and excellent shielding from electromagnetic radiation and cosmic rays.

Keywords: Dense interstellar clouds, Dark interstellar clouds, Interstellar clouds, Interstellar medium, Interstellar objects
Outflows from Super Star Clusters in the Central Starburst of NGC 253. Young massive clusters play an important role in the evolution of their host galaxies, and feedback from the high-mass stars in these clusters can have profound effects on the surrounding interstellar medium. The nuclear starburst in the nearby galaxy NGC 253 at a distance of 3.5 Mpc is a key laboratory in which to study star formation in an extreme environment. Previous high-resolution (1.9 pc) dust continuum observations from the Atacama Large Millimeter/submillimeter Array (ALMA) discovered 14 compact, massive super star clusters (SSCs) still in formation. We present here ALMA data at 350 GHz with 28 mas (0.5 pc) resolution. We detect blueshifted absorption and redshifted emission (P-Cygni profiles) toward three of these SSCs in multiple lines, including CS 7-6 and H13CN 4-3, which represent direct evidence for previously unobserved outflows. The mass contained in these outflows is a significant fraction of the cluster gas masses, which suggests we are witnessing a short but important phase. Further evidence of this is the finding of a molecular shell around the only SSC visible at near-IR wavelengths. We model the P-Cygni line profiles to constrain the outflow geometry, finding that the outflows must be nearly spherical. Through a comparison of the outflow properties with predictions from simulations, we find that none of the available mechanisms completely explains the observations, although dust-reprocessed radiation pressure and O star stellar winds are the most likely candidates. The observed outflows will have a very substantial effect on the clusters' evolution and star formation efficiency.

Keywords: Interstellar molecules, Starburst galaxies, Stellar feedback, Young massive clusters, Star formation, Interstellar medium, Galaxies, Star clusters
Deciphering Star Cluster Evolution by Shape Morphology. We analyze the morphological evolution of open clusters and provide shape parameters for 265 open clusters. The results show that the overall shape of sample clusters becomes more elliptical as they grow older, while their core remains circular or slightly trending to circular. There is a negative correlation of the ellipticities with the number of members of the sample clusters. A significant negative correlation between the overall ellipticities and masses is also detected for the sample clusters with log(age/year) ≥8, suggesting that the overall shapes of the clusters are possibly influenced by the number of members and masses, in addition to the external forces and the surrounding environment. For most young sample clusters, the radial stratification degree of the short-axis direction is greater than that of the long, implying that the radial stratification degree in the two directions within the young sample cluster may be unevenly affected by an internal evolutionary process. Older sample clusters exhibit lower stratification in the tangential direction, which possibly means those clusters may continue to survive for a long time at a low level of stratification. Our analysis shows that the overall shape of the sample clusters may be more susceptible to the influence of Galactic tides toward the Galactic center than the shear forces embedded in Galactic differential rotation. By analyzing the distribution of the ages and number of members of star clusters, we suggest that NGC 6791 may originate from superclusters.

Keywords: Open star clusters, Star clusters
A Coplanar Circumbinary Protoplanetary Disk in the TWA 3 Triple M Dwarf System. We present sensitive ALMA observations of TWA 3, a nearby, young (∼10 Myr) hierarchical system composed of three pre-main-sequence M3-M4.5 stars. For the first time, we detected 12CO and 13CO J = 2-1 emissions from the circumbinary protoplanetary disk around TWA 3A. We jointly fit the protoplanetary disk velocity field, stellar astrometric positions, and stellar radial velocities to infer the architecture of the system. The Aa and Ab stars (0.29 ± 0.01 M⊙ and 0.24 ± 0.01 M⊙, respectively) comprising the tight (P = 35 days) eccentric (e = 0.63 ± 0.01) spectroscopic binary are coplanar with their circumbinary disk (misalignment &lt;6° with 68% confidence), similar to other short-period binary systems. From models of the spectral energy distribution, we found the inner radius of the circumbinary disk (rinner = 0.50-0.75 au) to be consistent with theoretical predictions of dynamical truncation rcav/ainner ≈ 3. The outer orbit of the tertiary star B (0.40 ± 0.28 M⊙, a ∼ 65 ± 18 au, e = 0.3 ± 0.2) is not as well constrained as the inner orbit; however, orbits coplanar with the A system are still preferred (misalignment &lt; 20°). To better understand the influence of the B orbit on the TWA 3A circumbinary disk, we performed SPH simulations of the system and found that the outer edge of the gas disk (router = 8.5 ± 0.2 au) is most consistent with truncation from a coplanar, circular, or moderately eccentric orbit, supporting the preference from the joint orbital fit.

Keywords: Binary stars, Stellar dynamics, Pre-main sequence stars, Protoplanetary disks, Trinary stars
Neutral versus Ion Line Widths in Barnard 5: Evidence for Penetration by Magnetohydrodynamic Waves. Dense cores are the final place where turbulence is dissipated. It has been proposed from theoretical arguments that the nonthermal velocity dispersion should be narrower both for molecular ions (compared to neutrals) and for transitions with higher critical densities. To test these hypotheses, we compare the velocity dispersion of ${{\rm{N}}}_{2}{{\rm{H}}}^{+}$ (1-0) ( ${n}_{\mathrm{crit}}$ = 6 × 104 ${\mathrm{cm}}^{-3}$ ) and ${\mathrm{NH}}_{3}$ ( ${n}_{\mathrm{crit}}$ = 2 × 103 ${\mathrm{cm}}^{-3}$ ), in the dense core Barnard 5. We analyze well-resolved and high signal-to-noise observations of ${\mathrm{NH}}_{3}$ (1,1) and (2,2) obtained with combining Robert C. Byrd Green Bank Telescope (GBT) and Very Large Array (VLA) data, and ${{\rm{N}}}_{2}{{\rm{H}}}^{+}$ (1-0) obtained with GBT Argus, which present a similar morphology. Surprisingly, the nonthermal velocity dispersion of the ion is systematically higher than that of the neutral by 20%. The derived sonic Mach number, ${{ \mathcal M }}_{s}={\sigma }_{\mathrm{NT}}/{c}_{s}$ , has peak values ${{ \mathcal M }}_{s,{{\rm{N}}}_{2}{{\rm{H}}}^{+}}=0.59$ and ${{ \mathcal M }}_{s,{\mathrm{NH}}_{3}}=0.48$ for ${{\rm{N}}}_{2}{{\rm{H}}}^{+}$ and ${\mathrm{NH}}_{3}$ , respectively. This observed difference may indicate that the magnetic field even deep within the dense core is still oscillating, as it is in the turbulent region outside the core. The ions should be more strongly dynamically coupled to this oscillating field than the neutrals, thus accounting for their broader line width. If corroborated by further observations, this finding would shed additional light on the transition to quiescence in dense cores.

Keywords: Star formation, Interferometry, Astrochemistry