Sazuna/UAT_keywords huggingface dataset:
The Nature of Class I Sources: Periodic Variables in Orion. We present a quantitative, empirically based argument that at least some Class I sources are low-mass, pre-main-sequence stars surrounded by spatially extended envelopes of dusty gas. The source luminosity arises principally from stellar gravitational contraction, as in optically visible pre-main-sequence stars that lack such envelopes. We base our argument on the fact that some Class I sources in Orion and other star-forming regions have been observed by Spitzer to be periodic variables in the mid-infrared, and with periods consistent with T Tauri rotation rates. Using a radiative transfer code, we construct a variety of dust envelopes surrounding rotating, spotted stars, to see whether an envelope that produces a Class I spectral energy distribution at least broadly matches the observed modulations in luminosity. Acceptable envelopes can be either spherical or flattened and may or may not have polar cavities. The key requirement is that they have a modest equatorial optical depth at the Spitzer waveband of 3.6 μm, typically τ 3.6 ≈ 0.6. The total envelope mass, based on this limited study, is at most about 0.1 M ⊙, less than a typical stellar mass. Future studies should focus on the dynamics of the envelope, to determine whether material is actually falling onto the circumstellar disk.

Keywords: Starspots, Herbig Ae/Be stars, Circumstellar matter, T Tauri stars, Pre-main sequence stars, Protostars
The MOSDEF Survey: The Metallicity Dependence of X-Ray Binary Populations at z ∼ 2. Population synthesis models predict that high-mass X-ray binary (HMXB) populations produced in low-metallicity environments should be more X-ray luminous, a trend supported by studies of nearby galaxies. This trend may be responsible for the observed increase of the X-ray luminosity (L X) per star formation rate (SFR) with redshift due to the decrease of metallicity (Z) at fixed stellar mass as a function of redshift. To test this hypothesis, we use a sample of 79 z ∼ 2 star-forming galaxies with oxygen abundance measurements from the MOSDEF survey, which obtained rest-frame optical spectra for ∼1500 galaxies in the CANDELS fields at 1.37 &lt; z &lt; 3.80. Using Chandra data from the Chandra AEGIS-X Deep, Chandra Deep Field North, and Chandra Deep Field South surveys, we stack the X-ray data at the galaxy locations in bins of redshift and Z because the galaxies are too faint to be individually detected. In agreement with previous studies, the average L X/SFR of our z ∼ 2 galaxy sample is enhanced by ≈0.4-0.8 dex relative to local HMXB L X-SFR scaling relations. Splitting our sample by Z, we find that L X/SFR and Z are anticorrelated with 97% confidence. This observed Z dependence for HMXB-dominated galaxies is consistent with both the local L X-SFR-Z relation and a subset of population synthesis models. Although the statistical significance of the observed trends is weak owing to the low X-ray statistics, these results constitute the first direct evidence connecting the redshift evolution of L X/SFR and the Z dependence of HMXBs.

Keywords: X-ray binary stars, High mass x-ray binary stars, Galaxy abundances, Metallicity, High-redshift galaxies
Global 3D Hydrodynamic Modeling of In-transit Lyα Absorption of GJ 436b. Using a global 3D, fully self-consistent, multifluid hydrodynamic model, we simulate the escaping upper atmosphere of the warm Neptune GJ 436b, driven by the stellar X-ray and ultraviolet (XUV) radiation impact and gravitational forces and interacting with the stellar wind. Under the typical parameters of XUV flux and stellar wind plasma expected for GJ 436, we calculate in-transit absorption in Lyα and find that it is produced mostly by energetic neutral atoms outside of the planetary Roche lobe, due to the resonant thermal line broadening. At the same time, the influence of radiation pressure has been shown to be insignificant. The modeled absorption is in good agreement with the observations and reveals such features as strong asymmetry between blue and red wings of the absorbed Lyα line profile, deep transit depth in the high-velocity blue part of the line reaching more than 70%, and the timing of early ingress. On the other hand, the model produces significantly deeper and longer egress than in observations, indicating that there might be other processes and factors, still not accounted for, that affect the interaction between the planetary escaping material and the stellar wind. At the same time, it is possible that the observational data, collected in different measurement campaigns, are affected by strong variations of the stellar wind parameters between the visits, and therefore they cannot be reproduced altogether with the single set of model parameters.

Keywords: Hydrodynamical simulations, Space plasmas, Transits, Exoplanets, Hot Neptunes, Exoplanet atmospheres
2 mm GISMO Observations of the Galactic Center. I. Dust Emission. The central molecular zone, covering the inner ∼1° of the Galactic plane has been mapped at 2 mm using the Goddard-IRAM Superconducting 2-Millimeter Observer (GISMO) bolometric camera on the 30 m IRAM telescope. The 21″ resolution maps show abundant emission from cold molecular clouds, from star-forming regions, and from one of the Galactic center nonthermal filaments. In this work we use the Herschel Hi-GAL data to model the dust emission across the Galactic center. We find that a single-temperature fit can describe the 160-500 μm emission for most lines of sight, if the long-wavelength dust emissivity scales as λ -β  with β ≈ 2.25. This dust model is extrapolated to predict the 2 mm dust emission. Subtraction of the model from the GISMO data provides a clearer look at the 2 mm emission of star-forming regions and the brightest nonthermal filament. Based on observations carried out with the IRAM 30 m Telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).

Keywords: Interstellar dust, Galactic center, Millimeter astronomy, Far infrared astronomy, Dust continuum emission, Radio continuum emission
2 mm GISMO Observations of the Galactic Center. II. A Nonthermal Filament in the Radio Arc and Compact Sources. We have used the Goddard IRAM 2 Millimeter Observer (GISMO) with the 30 m IRAM telescope to carry out a 2 mm survey of the Galaxy’s central molecular zone. These observations detect thermal emission from cold interstellar medium dust, thermal free-free emission from ionized gas, and nonthermal synchrotron emission from relatively flat-spectrum sources. Archival data sets spanning 3.6 μm-90 cm are used to distinguish different emission mechanisms. After the thermal emission of dust is modeled and subtracted, the remaining 2 mm emission is dominated by free-free emission, with the exception of the brightest nonthermal filament (NTF) that runs through the middle of the bundle of filaments known as the Radio Arc. This is the shortest wavelength at which any NTF has been detected. The GISMO observations clearly trace this NTF over a length of ∼0.°2, with a mean 2 mm spectral index that is steeper than at longer wavelengths. The 2 mm-6 cm (or 20 cm) spectral index steepens from α ≈ -0.2 to -0.7 as a function distance from the Sickle H II region, suggesting that this region is directly related to the NTF. A number of unresolved (at 21″) 2 mm sources are found nearby. One appears to be thermal dust emission from a molecular cloud that is associated with an enigmatic radio point source whose connection to the Radio Arc is still debated. The morphology and colors at shorter IR wavelengths indicate other 2 mm unresolved sources are likely to be compact H II regions. Based on observations carried out with the IRAM 30 m Telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).

Keywords: Galactic center, Interstellar filaments, Millimeter astronomy, Interstellar thermal emission, Galactic radio sources, Interstellar synchrotron emission
Analysis of Helium-rich White Dwarfs Polluted by Heavy Elements in the Gaia Era. We present an analysis of 1023 DBZ/DZ(A) and 319 DQ white dwarf stars taken from the Montreal White Dwarf Database. This represents a significant increase over the previous comprehensive studies on these types of objects. We use new trigonometric parallax measurements from the Gaia second data release, together with photometry from the Sloan Digital Sky Survey, Pan-STARRS, Gaia, or BVRI from the literature, which allow the determination of the mass for the majority of the objects in our sample. We use the photometric and spectroscopic techniques with our recently improved model atmospheres code, which include high-density effects, to accurately determine the effective temperature, surface gravity, and heavy-element abundances for each object. We study the abundance of hydrogen in DBZ/DZ white dwarfs and the properties of the accreted planetesimals. We explore the nature of the second sequence of DQ stars using proper motions from Gaia and highlight evidence of crystallization in massive DQ stars. We also present mass distributions for both spectral types. Finally, we discuss the implications of our findings in the context of the spectral evolution of white dwarfs and provide the atmospheric parameters for each star.

Keywords: White dwarf stars
The Polarization Behavior of Relativistic Synchrotron Self-Compton Jets. We describe a geometric model for synchrotron and synchrotron self-Compton (SSC) radiation from blazar jets, involving multiple emission zones with turbulent magnetic fields and fully self-consistent seed photon mixing for SSC. Including the effects of jet divergence, particle cooling, and the relativistic PA rotation to the observer frame, we find that the multizone model recovers simple predictions for SSC polarization, but describes new dependencies on jet viewing geometry and zone multiplicity. Increasing the zone number decreases both synchrotron and SSC polarization, but with different scaling. A rise in synchrotron polarization fraction ΠSync at high energies is guaranteed by basic relativity considerations, and strengthened by jet nonuniformity. Finite light travel time effects can suppress the synchrotron polarization at energies well below the ν Sync peak. In general ΠSync and ΠSSC are correlated with ΠSSC/ΠSync ≈ 0.3, but individual realizations can lie far from this trend. This study lets us estimate Π across the SED, leading to predictions in the X-ray band helpful for planning observations with IXPE and other upcoming X-ray polarization missions.

Keywords: Blazars, Relativistic jets, Active galactic nuclei, Polarimetry
Simulated Interactions between Radio Galaxies and Cluster Shocks. II. Jet Axes Orthogonal to Shock Normals. We report a 3D MHD simulation study of the interactions between radio galaxies (RGs) and galaxy-cluster-media shocks in which the incident shock normals are orthogonal to the bipolar active galactic nucleus (AGN) jets. Before shock impact, light, supersonic jets inflate lobes (cavities) in a static, uniform intracluster medium. We examine three AGN activity scenarios: (1) continued, steady jet activity; (2) jet source cycled off coincident with shock/radio lobe impact; (3) jet activity ceased well before shock arrival (a “radio phoenix” scenario). The simulations follow relativistic electrons (CRe) introduced by the jets, enabling synthetic radio synchrotron images and spectra. Such encounters can be decomposed into an abrupt shock transition and a subsequent long-term postshock wind. Shock impact disrupts the preformed, low-density RG cavities into two ring vortices embedded in the postshock wind. Dynamical processes cause the vortex pair to merge as they propagate downwind somewhat faster than the wind itself. When the AGN jets remain active, ram pressure bends the jets downwind, generating a narrow angle tail morphology aligned with the axis of the vortex ring. The deflected jets do not significantly alter dynamical evolution of the vortex ring. However, active jets and their associated tails do dominate the synchrotron emission, compromising the observability of the vortex structures. Downwind-directed momentum concentrated by the jets impacts and alters the postencounter shock. In the “radio phoenix” scenario, no DSA of the fossil electron population is required to account for the observed brightening and flattening of the spectra; adiabatic compression effects are sufficient.

Keywords: Galaxy clusters, Radio lobes, Radio galaxies, Active galactic nuclei, Tailed radio galaxies, Shocks, Intracluster medium, Radio sources, Astronomical simulations, Magnetohydrodynamical simulations
Evolution of the Three-dimensional Shape of Passively Evolving and Star-forming Galaxies at z &lt; 1. Using the HST/ACS I F814W-band data, we investigated the distribution of apparent axial ratios of ∼21,000 galaxies with M  V  &lt; -20 at 0.2 &lt; z &lt; 1.0 in the COSMOS field as a function of stellar mass, specific star formation rate (sSFR), and redshift. We statistically estimated intrinsic 3D shapes of these galaxies by fitting the axial-ratio distribution with triaxial ellipsoid models characterized by face-on (middle-to-long) and edge-on (short-to-long) axial ratios B/A and C/A. We found that the transition from thin disk to thick spheroid occurs at ΔMS ∼ -1 dex, i.e., 10 times lower sSFR than that of the main sequence for galaxies with M star = 1010-1011 M ⊙ at 0.2 &lt; z &lt; 1.0. Furthermore, the intrinsic thickness (C/A) of passively evolving galaxies with M star = 1010-1011 M ⊙ significantly decreases with time from C/A ∼ 0.40-0.50 at z ∼ 0.8 to C/A ∼ 0.33-0.37 at z ∼ 0.4, while those galaxies with M star &gt; 1011 M ⊙ have C/A ∼ 0.5 irrespective of redshift. On the other hand, star-forming galaxies on the main sequence with 109.5-1011 M ⊙ show no significant evolution in their shape at 0.2 &lt; z &lt; 1.0, but their thickness depends on stellar mass; more massive star-forming galaxies tend to have lower C/A (thinner shape) than low-mass ones. These results suggest that some fraction of star-forming galaxies with a thin disk, which started to appear around z ∼ 1, quench their star formation without violent morphological change, and these newly added quiescent galaxies with a relatively thin shape cause the significant evolution in the axial-ratio distribution of passively evolving galaxies with M star &lt; 1011 M ⊙ at z &lt; 1.

Keywords: Galaxy quenching, Galaxy formation, Galaxy structure, Galaxy evolution
The Central Star of NGC 2346 as a Clue to Binary Evolution through the Common Envelope Phase. We present an analysis of the binary central star of the planetary nebula NGC 2346 based on archival data from the International Ultraviolet Explorer, and new low- and high-resolution optical spectra (3700-7300 Å). By including in the spectral analysis the contribution of both stellar and nebular continuum, we reconciled long-time discrepant UV and optical diagnostics and derive E(B-V) = 0.18 ± 0.01. We reclassified the companion star as A5IV by analyzing the wings of the Balmer absorption lines in the high-resolution (R = 67,000) optical spectra. Using the distance to the nebula of 1400 pc from Gaia DR2, we constructed a photoionization model based on abundances and line intensities derived from the low-resolution optical spectra, and obtained a temperature of T eff = 130,000 K and a luminosity of L = 170 L ⊙ for the ionizing star, consistent with the UV continuum. This analysis allows us to better characterize the binary system’s evolution. We conclude that the progenitor star of NGC 2346 has experienced a common envelope phase, in which the companion star has accreted mass and evolved off the main-sequence.

Keywords: Spectroscopic binary stars, Planetary nebulae, Binary stars, Chemical abundances
Hβ and Hγ Absorption-line Profile Inconsistencies in Laboratory Experiments Performed at White Dwarf Photosphere Conditions. The spectroscopic method relies on hydrogen Balmer absorption lines to infer white dwarf (WD) masses. These masses depend on the choice of atmosphere model, hydrogen atomic line shape calculation, and which Balmer series members are included in the spectral fit. In addition to those variables, spectroscopic masses disagree with those derived using other methods. Here we present laboratory experiments aimed at investigating the main component of the spectroscopic method: hydrogen line shape calculations. These experiments use X-rays from Sandia National Laboratories’ Z-machine to create a uniform ∼15 cm3 hydrogen plasma and a ∼4 eV backlighter that enables recording high-quality absorption spectra. The large plasma, volumetric X-ray heating that fosters plasma uniformity, and the ability to collect absorption spectra at WD photosphere conditions are improvements over past laboratory experiments. Analysis of the experimental absorption spectra reveals that electron density ({n}{{e}}) values derived from the Hγ line are ∼34% ± 7.3% lower than from Hβ. Two potential systematic errors that may contribute to this difference were investigated. A detailed evaluation of self-emission and plasma gradients shows that these phenomena are unlikely to produce any measurable Hβ-Hγ {n}{{e}} difference. WD masses inferred with the spectroscopic method are proportional to the photosphere density. Hence, the measured Hβ-Hγ {n}{{e}} difference is qualitatively consistent with the trend that WD masses inferred from their Hβ line are higher than that resulting from the analysis of Hβ and Hγ. This evidence may suggest that current hydrogen line shape calculations are not sufficiently accurate to capture the intricacies of the Balmer series.

Keywords: Atomic physics, Plasma physics, White dwarf stars, Laboratory astrophysics, DA stars
The Imprint of Spiral Arms on the Galactic Rotation Curve. We discuss a model for the Milky Way obtained by fitting the observed terminal velocities with the radial acceleration relation. The resulting stellar surface density profile departs from a smooth exponential disk, having bumps and wiggles that correspond to massive spiral arms. These features are used to estimate the term for the logarithmic density gradient in the Jeans equation, which turn out to have exactly the right location and amplitude to reconcile the apparent discrepancy between the stellar rotation curve and that of the interstellar gas. This model also predicts a gradually declining rotation curve outside the solar circle with slope -1.7 {km} {{{s}}}-1 {kpc}}-1, as subsequently observed.

Keywords: Milky Way dark matter halo, Gravitation, Milky Way dynamics, Milky Way rotation, Milky Way disk, Galaxy kinematics, Milky Way Galaxy, Milky Way mass
Finding the Critical Decay Index in Solar Prominence Eruptions. The background field is assumed to play a prime role in erupting structures like prominences. In the flux rope models, the critical decay index (n  c ) is a measure of the rate at which background field intensity decreases with height over the flux rope or erupting structure. In the real observations, the critical height of the background field is unknown, so a typical value of n  c  = 1.5 is adopted from numerical studies. In this study, we determined the n  c  of 10 prominence eruptions (PEs). The prominence height in 3D is derived from two-perspective observations of the Solar Dynamics Observatory and the Solar TErrestrial RElations Observatory. Synoptic maps of photospheric radial magnetic field are used to construct the background field in the corona. During the eruption, the height-time curve of the sample events exhibits the slow- and fast-rise phases and is fitted with the linear-cum-exponential model. From this model, the onset height of fast-rise motion is determined and is considered as the critical height for the onset of the torus instability because the erupting structure is allowed to expand exponentially provided there is no strapping background field. Corresponding to the critical height, the n  c  values of our sample events are varied to be in the range of 0.8-1.3. Additionally, the kinematic analysis suggests that the acceleration of PEs associated with flares are significantly enhanced compared to flareless PEs. We found that the flare magnetic reconnection is a more dominant contributor than the torus instability to the acceleration process during the fast-rise phase of flare-associated PEs in low corona (&lt;1.3R ☉).

Keywords: Solar active region magnetic fields, Eruptive phenomena, Solar prominences
Solar Fast-drifting Radio Bursts in an X1.3 Flare on 2014 April 25. One of the most important products of solar flares is nonthermal energetic particles, which may carry up to 50% of the energy released in the flaring processes. In radio observations, nonthermal particles generally manifest as spectral fine structures with fast frequency-drifting rates, named as solar fast-drifting radio bursts (FDRBs). This work demonstrated three types of FDRBs, including type III pair bursts, narrowband stochastic spike bursts following the type III bursts, and spike-like bursts superimposed on a type II burst in an X1.3 flare on 2014 April 25. We find that although all of them have fast frequency-drifting rates, they are intrinsically different from each other in frequency bandwidth, drifting rate, and statistical distribution. We suggest that they are possibly generated from different accelerating mechanisms. The type III pair bursts may be triggered by high-energy electron beams accelerated by the flaring magnetic reconnection, spike bursts are produced by the energetic electrons accelerated by a termination shock wave triggered by the fast reconnecting plasma outflows impacting the flaring loop top, and spike-like bursts are possibly generated by nonthermal electrons accelerated by moving magnetic reconnection triggered by interaction between coronal mass ejection and the background magnetized plasma. These results may help us to understand the generation mechanism of nonthermal particles and energy release in solar flares.

Keywords: Solar energetic particles, Solar coronal loops, Solar radio emission
Including Dust Coagulation in Hydrodynamic Models of Protoplanetary Disks: Dust Evolution in the Vicinity of a Jupiter-mass Planet. Dust growth is often neglected when building models of protoplanetary disks due to its complexity and computational expense. However, it does play a major role in shaping the evolution of protoplanetary dust and planet formation. In this paper, we present a numerical model coupling 2D hydrodynamic evolution of a protoplanetary disk, including a Jupiter-mass planet, and dust coagulation. This is obtained by including multiple dust fluids in a single grid-based hydrodynamic simulation and solving the Smoluchowski equation for dust coagulation on top of solving for the hydrodynamic evolution. We find that fragmentation of dust aggregates trapped in a pressure bump outside of the planetary gap leads to an enhancement in the density of small grains. We compare the results obtained from the full-coagulation treatment to the commonly used, fixed-dust-size approach and to previously applied, less computationally intensive methods for including dust coagulation. We find that the full-coagulation results cannot be reproduced using the fixed-size treatment, but some can be mimicked using a relatively simple method for estimating the characteristic dust size in every grid cell.

Keywords: Solar system gas giant planets, Computational methods, Protoplanetary disks, Exoplanet formation, Planet formation