Sazuna/UAT_keywords huggingface dataset:
EvryFlare. III. Temperature Evolution and Habitability Impacts of Dozens of Superflares Observed Simultaneously by Evryscope and TESS. Superflares may provide the dominant source of biologically relevant UV radiation to rocky habitable-zone M-dwarf planets (M-Earths), altering planetary atmospheres and conditions for surface life. The combined line and continuum flare emission has usually been approximated by a 9000 K blackbody. If superflares are hotter, then the UV emission may be 10 times higher than predicted from the optical. However, it is unknown for how long M-dwarf superflares reach temperatures above 9000 K. Only a handful of M-dwarf superflares have been recorded with multiwavelength high-cadence observations. We double the total number of events in the literature using simultaneous Evryscope and Transiting Exoplanet Survey Satellite observations to provide the first systematic exploration of the temperature evolution of M-dwarf superflares. We also increase the number of superflaring M dwarfs with published time-resolved blackbody evolution by ∼10×. We measure temperatures at 2 minutes cadence for 42 superflares from 27 K5-M5 dwarfs. We find superflare peak temperatures (defined as the mean of temperatures corresponding to flare FWHM) increase with flare energy and impulse. We find the amount of time flares emit at temperatures above 14,000 K depends on energy. We discover that 43% of the flares emit above 14,000 K, 23% emit above 20,000 K and 5% emit above 30,000 K. The largest and hottest flare briefly reached 42,000 K. Some do not reach 14,000 K. During superflares, we estimate M-Earths orbiting &lt;200 Myr stars typically receive a top-of-atmosphere UV-C flux of ∼120 W m-2 and up to 103 W m-2, 100-1000 times the time-averaged X-ray and UV flux from Proxima Cen.

Keywords: Ultraviolet astronomy, Astrobiology, Stellar flares, Optical flares, Exoplanet atmospheres
Exploring the Chemistry Induced by Energetic Processing of the H2-bearing, CO-rich Apolar Ice Layer. Interstellar ice mantles on the surfaces of dust grains are thought to have a bilayered structure, with a H2O-rich polar layer, covered by a CO-rich apolar layer that probably harbors H2 and other volatiles such as N2. In this work, we explore the chemistry induced by 2 keV electrons and Lyα photons in H2:CO:15N2 ice analogs of the CO-rich layer when exposed to similar fluences to those expected from the cosmic-ray-induced secondary electrons and UV photons during the typical lifetime of dense clouds. Six products were identified upon 2 keV electron irradiation: CO2, C2O (and other carbon chain oxides), CH4, H2CO, H2C2O, and H15NCO. The total product abundances corresponded to 5%-10% of the initial CO molecules exposed to electron irradiation. Lyα photon irradiation delivered one to two orders of magnitude lower yields with a similar product branching ratio, which may be due to the low UV-photon absorption cross section of the ice sample at this wavelength. Formation of additional N-bearing species, namely C215N2 and 15NH3, was only observed in the absence of H2 and CO molecules, respectively, suggesting that reactants derived from H2 and CO molecules preferentially react with each other instead of with 15N2 and its dissociation products. In summary, ice chemistry induced by energetic processing of the CO-rich apolar ice layer provides alternative formation pathways for several species detected in the interstellar medium, including some related to the complex organic molecule chemistry. Further quantification of these pathways will help astrochemical models constrain their relative contribution to the interstellar budget of, especially, the organic species H2CO and HNCO.

Keywords: Interstellar molecules, Laboratory astrophysics, Experimental techniques, Dense interstellar clouds, Cosmic rays
The Mean Absorption-line Spectra of a Selection of Luminous z ∼ 6 Lyman Break Galaxies. We examine the absorption-line spectra of a sample of 31 luminous ( ${M}_{\mathrm{UV}}\simeq -23$ ) Lyman break galaxies at redshift z ≃ 6 using data taken with the FOCAS and OSIRIS spectrographs on the Subaru and GTC telescopes. For two of these sources we present longer exposure data taken at higher spectral resolutions from ESO's X-shooter spectrograph. Using these data, we demonstrate the practicality of stacking our lower-resolution data to measure the depth of various interstellar and stellar absorption lines to probe the covering fraction of low-ionization gas and the gas phase and stellar metallicities near the end of the era of cosmic reionization. From maximum absorption-line depths of Si IIλ1260 and C IIλ1334, we infer a mean covering fraction of ≥0.85 ± 0.16 for our sample. This is larger than that determined using similar methods for lower-luminosity galaxies at slightly lower redshifts, suggesting that the most luminous galaxies appear to have a lower escape fraction than fainter galaxies, and therefore may not play a prominent role in concluding reionization. Using various interstellar absorption lines we deduce gas-phase metallicities close to solar, indicative of substantial early enrichment. Using selected stellar absorption lines, we model our spectra with a range of metallicities using techniques successfully employed at lower redshift and deduce a stellar metallicity of ${0.4}_{-0.1}^{+0.3}$ solar, consistent with the stellar mass—stellar metallicity relation recently found at z ∼ 3-5. We discuss the implications of these metallicity estimates for the typical ages of our luminous galaxies and conclude our results imply initial star formation at redshifts z ∼ 10, consistent with independent analyses of earlier objects.

Keywords: Reionization, Galaxy formation, Galaxy evolution
A Survey of 3-5.4 μm Emission from Planetary Nebulae Using SOFIA/FLITECAM. Here we present the results of an airborne 3-5.4 μm spectroscopic study of three young, carbon-rich planetary nebulae (PNs) IC 5117, PNG 093.9-00.1, and BD +30 3639. These observations were made using the grism spectroscopy mode of the First Light Infrared TEst CAMera (FLITECAM) instrument during airborne science operations on board NASA's Stratospheric Observatory for Infrared Astronomy (SOFIA). The goal of this study is to characterize the 3.3 and 5.25 μm polycyclic aromatic hydrocarbon (PAH) dust emission in PNs and study the evolution of PAH features within evolved stars before their incorporation into new stellar systems in star-forming regions. Targets were selected from Infrared Astronomical Satellite, Kuiper Airborne Observatory and Infrared Space Observatory source lists, and were previously observed with FLITECAM on the 3 m Shane telescope at Lick Observatory to allow direct comparison between the ground and airborne observations. We measure PAH emission equivalent width and central wavelength, classify the shape of the PAH emission, and determine the PAH/aliphatic ratio for each target. The 3.3 μm PAH emission feature is observed in all three objects. PNG 093.9-00.1 exhibits NGC 7027-like aliphatic emission in the 3.4-3.6 μm region while IC 5117 and BD +30 3639 exhibit less aliphatic structure. All three PNs additionally exhibit PAH emission at 5.25 μm.

Keywords: Post-asymptotic giant branch stars, Polycyclic aromatic hydrocarbons, Infrared astronomy, Planetary nebulae, Spectroscopy, Infrared observatories
The Milky Way's Shell Structure Reveals the Time of a Radial Collision. We identify shell structures in the Milky Way for the first time. We find two shells in the Virgo Overdensity region and two shells in the Hercules Aquila Cloud region using Sloan Digital Sky Survey, Gaia, and LAMOST data. These shell stars are a subset of the substructure previously identified as the Virgo Radial Merger (VRM). Timing arguments for these shells indicate that their progenitor dwarf galaxy passed through the Galactic center 2.7 ± 0.2 Gyr ago. Based on the time of collision, it is also possible that the VRM is related to the phenomenon that created phase-space spirals in the vertical motion of the disk and/or the Splash and could have caused a burst of star formation in the inner disk. We analyze phase mixing in a collection of radial merger N-body simulations and find that shell structure similar to that observed in Milky Way data disappears by 5 Gyr after collision with the Galactic center. The method used to calculate the merger time of the VRM was able to reliably recover the correct merger times for these simulations. Previous work supports the idea that the VRM and the Gaia Sausage/Gaia-Enceladus Merger are the same. However, the Gaia Sausage is widely believed to be 8-11 Gyr old. The disparate ages could be reconciled if the larger age is associated with an infall time when the progenitor crossed the virial radius; we do not constrain the time at which the progenitor became bound to the Milky Way. Alternatively, the Gaia Sausage could be younger than previously thought.

Keywords: Galaxy stellar halos, Galaxy dynamics, Milky Way Galaxy
Maps of the Number of H I Clouds along the Line of Sight at High Galactic Latitude. Characterizing the structure of the Galactic interstellar medium (ISM) in three dimensions is of high importance for accurate modeling of dust emission as a foreground to the cosmic microwave background (CMB). At high Galactic latitude, where the total dust content is low, accurate maps of the 3D structure of the ISM are lacking. We develop a method to quantify the complexity of the distribution of dust along the line of sight with the use of H I line emission. The method relies on a Gaussian decomposition of the H I spectra to disentangle the emission from overlapping components in velocity. We use this information to create maps of the number of clouds along the line of sight. We apply the method to (a) the high Galactic latitude sky and (b) the region targeted by the BICEP/Keck experiment. In the north Galactic cap we find on average three clouds per 0.2 square degree pixel, while in the south the number falls to 2.5. The statistics of the number of clouds are affected by intermediate-velocity clouds (IVCs), primarily in the north. IVCs produce detectable features in the dust emission measured by Planck. We investigate the complexity of H I spectra in the BICEP/Keck region and find evidence for the existence of multiple components along the line of sight. The data (doi: 10.7910/DVN/8DA5LH) and software are made publicly available and can be used to inform CMB foreground modeling and 3D dust mapping.

Keywords: Neutral hydrogen clouds, Interstellar medium, Interstellar atomic gas
Monte Carlo Calculations of Helium Escape on Mars via Energy Transfer from Hot Oxygen Atoms. Understanding He escape is crucial for deciphering the evolution of the He budget on Mars. A number of viable mechanisms have been proposed to drive He escape, with energy transfer from hot O generally thought to be the dominant one. This study is devoted to a state-of-the-art evaluation of the above process assuming hot O is exclusively produced from the dissociative recombination of O2+ in the Martian ionosphere. A Monte Carlo model is constructed, with model inputs optimized by the recent Mars Atmosphere and Volatile Evolution measurements. The model calculations reveal a dayside He escape flux of (1-2) × 106 cm-2 s-1 referred to the surface, for a possible range of H2 mixing ratio at an altitude of 80 km from 0 to 40 ppm. The computed He escape flux increases with increasing nascent O energy and decreasing atmospheric H2 and H abundances. The portion of the atmosphere below the exobase is found to make an exceptionally large contribution of 95% to He escape.

Keywords: Upper atmosphere, Exosphere, Mars, Planetary atmospheres, Aeronomy
Supernovae in Orion: The Missing Link in the Star-forming History of the Region. The Orion Complex is a notable star-forming region fragmented into several different populations with substantial differences in their phase space. I propose a model that attempts to explain the how the Complex has evolved into this current configuration. In the model presented here, the large-scale expansion can be attributable to a supernova that exploded 6 Myr ago. The remnants of this explosion can be seen as Barnard's loop, as the center of the expansion is consistent with the geometrical center of the H II bubble. This is similar to the H II bubble and the ballistic expansion that is associated with λ Ori, a region that was also the site of an ancient supernova. Assuming that the Orion Complex originally formed as one long filament spanning from the bottom of Orion A to ψ2 Ori (or potentially as far as λ Ori), Barnard's loop supernova could have split the cloud, which led to the formation of Orion C &amp; D. Furthermore, the shockwave that propagated into the filament could have swept along the gas through several parsecs, which led to the formation of the singularly most massive cluster in the solar neighborhood, the Orion Nebula Cluster. I also discuss other related nearby events, such as the formation of the Monogem ring and various runaways that have been ejected from the Orion Complex.

Keywords: Stellar feedback, Stellar populations, Young star clusters, Supernova remnants, H II regions, Star formation, Runaway stars
The MOSDEF Survey: The First Direct Measurements of the Nebular Dust Attenuation Curve at High Redshift. We use a sample of 532 star-forming galaxies at redshifts z ≃ 1.4-2.6 with deep rest-frame optical spectra from the MOSFIRE Deep Evolution Field (MOSDEF) survey to place the first constraints on the nebular attenuation curve at high redshift. Based on the first five low-order Balmer emission lines detected in the composite spectra of these galaxies (Hα through ${\rm{H}}\epsilon $ ), we derive a nebular attenuation curve that is similar in shape to that of the Galactic extinction curve, suggesting that the dust covering fraction and absorption/scattering properties along the lines of sight to massive stars at high redshift are similar to those of the average Milky Way sight line. The curve derived here implies nebular reddening values that are, on average, systematically larger than those derived for the stellar continuum. In the context of stellar population synthesis models that include the effects of stellar multiplicity, the difference in reddening of the nebular lines and stellar continuum may imply molecular cloud crossing timescales that are a factor of $\gtrsim 3\times $ longer than those inferred for local molecular clouds, star formation rates that are constant or increasing with time such that newly formed and dustier OB associations always dominate the ionizing flux, and/or that the dust responsible for reddening the nebular emission may be associated with nonmolecular (i.e., ionized and neutral) phases of the interstellar medium. Our analysis points to a variety of investigations of the nebular attenuation curve that will be enabled with the next generation of ground- and space-based facilities. * Based on data obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA and was made possible by the generous financial support of the W.M. Keck Foundation.

Keywords: Interstellar dust, Interstellar dust extinction, Reddening law, Interstellar reddening, Galaxy evolution, Interstellar extinction, High-redshift galaxies
Radial Distributions of Dwarf Satellite Systems in the Local Volume. The radial spatial distribution of low-mass satellites around a Milky Way (MW)-like host is an important benchmark for simulations of small-scale structure. The distribution is sensitive to the disruption of subhalos by the central disk and can indicate whether the disruption observed in simulations of MW analogs is artificial (i.e., numerical) or physical in origin. We consider a sample of 12 well-surveyed satellite systems of MW-like hosts in the Local Volume (D &lt; 12 Mpc) that are complete to MV &lt; -9 and within 150 projected kpc. We investigate the radial distribution of satellites and compare with ΛCDM cosmological simulations, including big-box cosmological simulations and high-resolution zoom-in simulations of MW-sized halos. We find that the observed satellites are significantly more centrally concentrated than the simulated systems. Several of the observed hosts, including the MW, are ∼2σ outliers relative to the simulated hosts in being too concentrated, while none of the observed hosts are less centrally concentrated than the simulations. This result is robust to different ways of measuring the radial concentration. We find that this discrepancy is more significant for bright, MV &lt; -12 satellites, suggestive that this is not the result of observational incompleteness. We argue that the discrepancy is possibly due to artificial disruption in the simulations, but, if so, this has important ramifications for what relation between stellar mass and halo mass is allowed in the low-mass regime by the observed abundance of satellites.

Keywords: Local Group, Dwarf galaxies, Dark matter, Milky Way Galaxy
Formation and Evolution of Ultraluminous X-Ray Pulsar Binaries to Pulsar-Neutron Star and Pulsar-White Dwarf Systems. Recent observational and theoretical results have suggested that some of ultraluminous X-ray (ULX) sources may contain neutron star (NS) accretors. However, the formation channel and properties of donor stars of NS ULXs remain uncertain. By adopting the nonconservative and rotation-dependent mass transfer model in the primordial binary evolution, we investigate the way to form pulsar ULXs like observed pulsar ULXs in a systematic way. Our simulation results indicate that pulsar ULXs with Be stars and intermediate or/and high-mass donors match observed apparent luminosities, orbital periods, and observationally indicated donor masses of known pulsar ULXs. ULXs with Be and intermediate donors are main contributors. The route of accretion-induced collapse of WDs has a 4.5% contribution to the NS ULXs, 4.0% of NSs in ULXs are formed through electron-capture supernovae (SNe), and 91.5% of NSs in ULXs are born with core-collapse SNe. We also studied the evolution of pulsar ULXs to double compact star systems. We do not find NS-black hole systems (merging in a Hubble time) that evolved from pulsar ULXs. Pulsar-white dwarf (WD) cases that evolve through pulsar ULXs have significant contributions to the whole NS-WD gravitational wave sources. Contributions of pulsar-WD and pulsar-NS cases that experienced pulsar ULXs are ∼40% and 11% among all LISA NS-WD and NS-NS sources, respectively. Monte Carlo simulation noise with different models give a nonnegligible uncertainty.

Keywords: X-ray binary stars, Binary stars, Close binary stars, White dwarf stars, Gravitational wave sources, Pulsars, Compact objects
Hydrogen Recombination Line Luminosities and Variability from Forming Planets. We calculated hydrogen recombination line luminosities (H-α, Paschen-β and Brackett-γ) from 3D thermohydrodynamical simulations of forming planets from 1 to 10 Jupiter mass (MJup). We explored various opacities to estimate the line emissions with extinction, in each case assuming boundary-layer accretion. When realistic opacities are considered, only lines from planets ≥10 MJup can be detected with current instrumentation, highlighting that most planets do not have detectable emission. This might explain the very low detection rate of H-α from forming planets from observations. While the line emission comes from both the forming planet and its circumplanetary disk, we found that only the disk component could be detected due to extinction. We examined the line variability as well, and found that it is higher for higher-mass planets. Furthermore, we determine for the first time the parametric relationship between the mass of the planet and the luminosity of the hydrogen recombination lines, as well as the equation between the accretion luminosity and hydrogen recombination line luminosities.

Keywords: Accretion, Photoionization, Protoplanetary disks, Exoplanet detection methods, Extrasolar gaseous giant planets
Infrared Excesses around Bright White Dwarfs from Gaia and unWISE. I.. Studies of excess infrared radiation around white dwarfs provide important constraints on the evolution of planetary systems and low-mass companions beyond the main-sequence stage. In this paper series, we focus on identifying and characterizing bright white dwarfs with an infrared excess. Here, we present 188 infrared excess candidates from Gaia and unWISE, 147 of which are new discoveries. Further characterization of this sample can significantly increase the current list of white dwarf debris disks and white dwarfs with low-mass companions.

Keywords: White dwarf stars, Brown dwarfs, Circumstellar disks
A Quasi-linear Diffusion Model for Resonant Wave-Particle Instability in Homogeneous Plasma. In this paper, we develop a model to describe the generalized wave-particle instability in a quasi-neutral plasma. We analyze the quasi-linear diffusion equation for particles by expressing an arbitrary unstable and resonant wave mode as a Gaussian wave packet, allowing for an arbitrary direction of propagation with respect to the background magnetic field. We show that the localized energy density of the Gaussian wave packet determines the velocity-space range in which the dominant wave-particle instability and counteracting damping contributions are effective. Moreover, we derive a relation describing the diffusive trajectories of resonant particles in velocity space under the action of such an interplay between the wave-particle instability and damping. For the numerical computation of our theoretical model, we develop a mathematical approach based on the Crank-Nicolson scheme to solve the full quasi-linear diffusion equation. Our numerical analysis solves the time evolution of the velocity distribution function under the action of a dominant wave-particle instability and counteracting damping and shows a good agreement with our theoretical description. As an application, we use our model to study the oblique fast-magnetosonic/whistler instability, which is proposed as a scattering mechanism for strahl electrons in the solar wind. In addition, we numerically solve the full Fokker-Planck equation to compute the time evolution of the electron-strahl distribution function under the action of Coulomb collisions with core electrons and protons after the collisionless action of the oblique fast-magnetosonic/whistler instability.

Keywords: Space plasmas, Solar wind, Plasma astrophysics
Teaching Neural Networks to Generate Fast Sunyaev-Zel'dovich Maps. The thermal Sunyaev-Zel'dovich (tSZ) and the kinematic Sunyaev-Zel'dovich (kSZ) effects trace the distribution of electron pressure and momentum in the hot universe. These observables depend on rich multiscale physics, thus, simulated maps should ideally be based on calculations that capture baryonic feedback effects such as cooling, star formation, and other complex processes. In this paper, we train deep convolutional neural networks with a U-Net architecture to map from the three-dimensional distribution of dark matter to electron density, momentum, and pressure at ∼100 kpc resolution. These networks are trained on a combination of the TNG300 volume and a set of cluster zoom-in simulations from the IllustrisTNG project. The neural nets are able to reproduce the power spectrum, one-point probability distribution function, bispectrum, and cross-correlation coefficients of the simulations more accurately than the state-of-the-art semianalytical models. Our approach offers a route to capture the richness of a full cosmological hydrodynamical simulation of galaxy formation with the speed of an analytical calculation.

Keywords: Hydrodynamical simulations, Convolutional neural networks, Sunyaev-Zeldovich effect, Large-scale structure of the universe