Sazuna/UAT_keywords huggingface dataset:
The Astrophysical Variance in Gaia-Radial Velocity Spectrometer Spectra. Large surveys are providing a diversity of spectroscopic observations with Gaia alone set to deliver millions of Ca-triplet-region spectra across the Galaxy. We aim to understand the dimensionality of the chemical abundance information in the Gaia-Radial Velocity Spectrometer (RVS) data to inform galactic archeology pursuits. We fit a quadratic model of four primary sources of variability, described by labels of Teff, $\mathrm{log}g$ , [Fe/H], and [α/Fe], to the normalized flux of 10,802 red-clump stars from the Gaia-RVS-like Abundances and Radial velocity Galactic Origins Survey (ARGOS). We examine the residuals between ARGOS spectra and the models and find that the models capture the flux variability across 85% of the wavelength region. The remaining residual variance is concentrated to the Ca-triplet features, at an amplitude up to 12% of the normalized flux. We use principal component analysis on the residuals and find orthogonal correlations in the Ca-triplet core and wings. This variability, not captured by our model, presumably marks departures from the completeness of the 1D LTE label description. To test the indication of low-dimensionality, we turn to abundance-space to infer how well we can predict measured [Si/H], [O/H], [Ca/H], [Ni/H], and [Al/H] abundances from the Gaia-RVS-like Radial Velocity Experiment survey with models of Teff, $\mathrm{log}g$ , [Fe/H], and [Mg/Fe]. We find that we can nearly entirely predict these abundances. Using high-precision Apache Point Observatory Galactic Evolution Experiment abundances, we determine that a measurement uncertainty of &lt;0.03 dex is required to capture additional information from these elements. This indicates that a four-label model sufficiently describes chemical abundance variance for an approximate signal-to-noise ratio &lt;200 per pixel, in Gaia-RVS spectra.

Keywords: Stellar astronomy, Galactic archaeology, Chemical abundances
Differential Source Count for Gamma-Ray Bursts. Different forms of long gamma-ray burst (GRB) luminosity functions are considered on the basis of an explicit physical model. The inferred flux distributions are compared with the observed ones from two samples of GRBs, Swift and Fermi GBM. The best-fit parameters of the luminosity functions are found, and the physical interpretations are discussed. The results are consistent with the observation of a comparable number of flat-phase afterglows and monotonically decreasing ones.

Keywords: Gamma-ray bursts
Searches for Continuous Gravitational Waves from Young Supernova Remnants in the Early Third Observing Run of Advanced LIGO and Virgo. We present results of three wide-band directed searches for continuous gravitational waves from 15 young supernova remnants in the first half of the third Advanced LIGO and Virgo observing run. We use three search pipelines with distinct signal models and methods of identifying noise artifacts. Without ephemerides of these sources, the searches are conducted over a fRequency band spanning from 10 to 2 kHz. We find no evidence of continuous gravitational radiation from these sources. We set upper limits on the intrinsic signal strain at 95% confidence level in sample subbands, estimate the sensitivity in the full band, and derive the corresponding constraints on the fiducial neutron star ellipticity and r-mode amplitude. The best 95% confidence constraints placed on the signal strain are 7.7 × 10‑26 and 7.8 × 10‑26 near 200 Hz for the supernova remnants G39.2–0.3 and G65.7+1.2, respectively. The most stringent constraints on the ellipticity and r-mode amplitude reach ≲10‑7 and ≲ 10‑5, respectively, at frequencies above ∼400 Hz for the closest supernova remnant G266.2–1.2/Vela Jr.

Keywords: Gravitational wave astronomy, Neutron stars, Supernova remnants, Gravitational waves
The Young Stellar Population, Distance, and Cloud-Cloud Collision Induced Star Formation Scenario of the Trifid Nebula. The Trifid Nebula is a young, nearby star-forming region where star formation is proposed to have been triggered by cloud-cloud collision (CCC), based on observations of molecular clouds. It offers a unique opportunity to test whether the CCC hypothesis is supported by the spatial distribution and star formation chronology of young stars. We present the first study of the optically visible pre-main sequence (PMS) population of the region using riHα imaging and Gaia astrometry. Combined with an analysis of young stellar objects (YSOs) using infrared imaging, we capture the spatial distribution and star formation chronology of the young stellar population. From the analysis, 15 Flat/Class I YSOs, 46 Class II YSOs, and 41 accreting PMS stars are identified (diskless/non-accreting sources are not included in the analysis). The distance based on Gaia parallaxes is ~1250 pc, significantly closer than previously reported. The Class II YSOs and PMS stars (~1.5 Myr old) are spread toward the edge of the molecular clouds. They are slightly younger than the estimated crossing time of ~2.7 Myr and closer to the estimated dynamical age ~0.85 Myr. Younger Class I YSOs are more concentrated spatially. There exists a cavity devoid of young stars where the two clouds overlap. This evidence suggests that the current generation of stars formed after the collision of two clouds ~1 Myr ago, and this result can be corroborated using future spectroscopic studies.

Keywords: Star forming regions, Young stellar objects, Pre-main sequence stars, Star formation, H II regions
The Solar Memory from Hours to Decades. Waiting-time distributions allow us to distinguish at least three different types of dynamical systems, including (i) linear random processes (with no memory); (ii) nonlinear, avalanche-type, nonstationary Poisson processes (with memory during the exponential growth of the avalanche rise time); and (iii) chaotic systems in the state of a nonlinear limit cycle (with memory during the oscillatory phase). We describe the temporal evolution of the flare rate λ(t) ∝ tp with a polynomial function, which allows us to distinguish linear (p ≈ 1) from nonlinear (p ≳ 2) events. The power-law slopes α of the observed waiting times (with full solar cycle coverage) cover a range of α = 2.1-2.4, which agrees well with our prediction of α = 2.0 + 1/p = 2.3-2.6. The memory time can also be defined with the time evolution of the logistic equation, for which we find a relationship between the nonlinear growth time τG = τrise/(4p) and the nonlinearity index p. We find a nonlinear evolution for most events, in particular for the clustering of solar flares (p = 2.2 ± 0.1), partially occulted flare events (p = 1.8 ± 0.2), and the solar dynamo (p = 2.8 ± 0.5). The Sun exhibits memory on timescales of ≲2 hr to 3 days (for solar flare clustering), 6-23 days (for partially occulted flare events), and 1.5 month to 1 yr (for the rise time of the solar dynamo).

Keywords: Solar flares, Solar x-ray flares
Ambipolar Electric Field and Potential in the Solar Wind Estimated from Electron Velocity Distribution Functions. The solar wind escapes from the solar corona and is accelerated, over a short distance, to its terminal velocity. The energy balance associated with this acceleration remains poorly understood. To quantify the global electrostatic contribution to the solar wind dynamics, we empirically estimate the ambipolar electric field (E∥) and potential (Φr,∞). We analyze electron velocity distribution functions (VDFs) measured in the near-Sun solar wind between 20.3 RS and 85.3 RS by the Parker Solar Probe. We test the predictions of two different solar wind models. Close to the Sun, the VDFs exhibit a suprathermal electron deficit in the sunward, magnetic-field-aligned part of phase space. We argue that the sunward deficit is a remnant of the electron cutoff predicted by collisionless exospheric models. This cutoff energy is directly linked to Φr,∞. Competing effects of E∥ and Coulomb collisions in the solar wind are addressed by the Steady Electron Runaway Model (SERM). In this model, electron phase space is separated into collisionally overdamped and underdamped regions. We assume that this boundary velocity at small pitch angles coincides with the strahl break-point energy, which allows us to calculate E∥. The obtained Φr,∞ and E∥ agree well with theoretical expectations. They decrease with radial distance as power-law functions with indices αΦ = -0.66 and αE = -1.69. We finally estimate the velocity gained by protons from electrostatic acceleration, which equals 77% calculated from the exospheric models, and 44% from the SERM model.

Keywords: Space plasmas, Space vehicle instruments, Solar wind, Collision physics, Interplanetary particle acceleration
Linking Outer Disk Pebble Dynamics and Gaps to Inner Disk Water Enrichment. Millimeter continuum imaging of protoplanetary disks reveals the distribution of solid particles and the presence of substructures (gaps and rings) beyond 5-10 au, while infrared (IR) spectra provide access to abundances of gaseous species at smaller disk radii. Building on recent observational findings of an anti-correlation between the inner disk water luminosity and outer dust disk radius, we aim here at investigating the dynamics of icy solids that drift from the outer disk and sublimate their ice inside the snow line, enriching the water vapor that is observed in the IR. We use a volatile-inclusive disk evolution model to explore a range of conditions (gap location, particle size, disk mass, and α viscosity) under which gaps in the outer disk efficiently block the inward drift of icy solids. We find that inner disk vapor enrichment is highly sensitive to the location of a disk gap, yielding for each particle size a radial "sweet spot" that reduces the inner disk vapor enrichment to a minimum. For pebbles of 1-10 mm in size, which carry the most mass, this sweet spot is at 7-15 au, suggesting that inner gaps may have a key role in reducing ice delivery to the inner disk and may not allow the formation of Earths and super-Earths. This highlights the importance of observationally determining the presence and properties of inner gaps in disks. Finally, we argue that the inner water vapor abundance can be used as a proxy for estimating the pebble drift efficiency and mass flux entering the inner disk.

Keywords: Exoplanets, Protoplanetary disks, Planet formation
Espresso and Stochastic Acceleration of Ultra-high-energy Cosmic Rays in Relativistic Jets. In the espresso scenario, ultra-high-energy (UHE) cosmic rays (CRs) are produced via a one-shot reacceleration of galactic-like CRs in the relativistic jets of active galactic nuclei, independently of the scattering rate dictated by magnetic fluctuations. In Mbarek &amp; Caprioli (2019) we traced test-particle CRs in high-resolution magnetohyrodynamic (MHD) jet simulations and found that the associated spectral slope, chemical composition, and anisotropy are consistent with UHECR phenomenology. In this work, we extend such an analysis by including subgrid pitch-angle scattering to model small-scale magnetic turbulence that cannot be resolved by MHD simulations. We find that a large scattering rate unlocks stochastic acceleration and fosters the energization of lower-energy CRs, which eventually leads to harder UHECR spectra. Yet, the particles that achieve the highest energies (up to the Hillas limit) are invariably produced by espresso acceleration and their spectrum is independent of the assumed subgrid scattering rate.

Keywords: Magnetohydrodynamical simulations, Active galactic nuclei, Ultra-high-energy cosmic radiation, Cosmic rays
Detection of H<SUB>2</SUB> in the TWA 7 System: A Probable Circumstellar Origin. Using HST-COS far-UV spectra, we have discovered warm molecular hydrogen in the TWA 7 system. TWA 7, a ~9 Myr old M2.5 star, has a cold debris disk and has previously shown no signs of accretion. Molecular hydrogen is expected to be extremely rare in a debris disk. While molecular hydrogen can be produced in starspots or the lower chromospheres of cool stars such as TWA 7, fluxes from progressions that get pumped by the wings of Lyα indicate that this molecular hydrogen could be circumstellar and thus that TWA 7 is accreting at very low levels and may retain a reservoir of gas in the near circumstellar environment.

Keywords: High resolution spectroscopy, Ultraviolet astronomy, T Tauri stars, Protoplanetary disks, Debris disks, Planet formation, Circumstellar gas
Radiative Turbulent Flares in Magnetically Dominated Plasmas. We perform 2D and 3D kinetic simulations of reconnection-mediated turbulent flares in a magnetized electron-positron plasma, with weak and strong radiative cooling. Such flares can be generated around neutron stars and accreting black holes. We focus on the magnetically dominated regime where tension of the background magnetic field lines exceeds the plasma rest-mass density by a factor σ0 &gt; 1. In the simulations, turbulence is excited on a macroscopic scale l0, and we observe that it develops by forming thin, dynamic current sheets on various scales. The deposited macroscopic energy dissipates by energizing thermal and nonthermal particles. The particle energy distribution is shaped by impulsive acceleration in reconnecting current sheets, gradual stochastic acceleration, and radiative losses. We parameterize radiative cooling by the ratio ${ \mathcal A }$ of light-crossing time l0/c to a cooling timescale, and study the effect of increasing ${ \mathcal A }$ on the flare. When radiative losses are sufficiently weak, ${ \mathcal A }\lt {\sigma }_{0}^{-1}$ , the produced emission is dominated by stochastically accelerated particles, and the radiative power depends logarithmically on ${ \mathcal A }$ . The resulting radiation spectrum of the flare is broad and anisotropic. In the strong-cooling regime, ${ \mathcal A }\gt {\sigma }_{0}^{-1}$ , stochastic acceleration is suppressed, while impulsive acceleration in the current sheets continues to operate. As ${ \mathcal A }$ increases further, the emission becomes dominated by thermal particles. Our simulations offer a new tool to study particle acceleration by turbulence, especially at high energies, where cooling competes with acceleration. We find that the particle distribution is influenced by strong intermittency of dissipation, and stochastic acceleration cannot be described by a universal diffusion coefficient.

Keywords: Computational astronomy, High energy astrophysics, Astrophysical magnetism, Plasma astrophysics, Non-thermal radiation sources, Compact objects
Estimating the Effective Lifetime of the z   6 Quasar Population from the Composite Proximity Zone Profile. The lifetime of quasars can be estimated by means of their proximity zone sizes, which are regions of enhanced flux blueward of the Lyα emission line observed in the rest-frame UV spectra of high-redshift quasars because the intergalactic gas has a finite response time to the quasars' radiation. We estimate the effective lifetime of the high-redshift quasar population from the composite transmitted flux profile within the proximity zone region of a sample of 15 quasars at 5.8 ≤ z ≤ 6.6 with precise systemic redshifts, and similar luminosities, i.e., -27.6 ≤ M1450 ≤ -26.4, and thus a similar instantaneous ionizing power. We develop a Bayesian method to infer the effective lifetime from the composite spectrum, including robust estimates of various sources of uncertainty on the spectrum. We estimate an effective lifetime of the quasar population as a whole of ${\mathrm{log}}_{10}({t}_{{\rm{Q}}}/\mathrm{yr})={5.7}_{-0.3(-0.5)}^{+0.5(+0.8)}$ given by the median and 68th (95th) percentile of the posterior probability distribution. While our result is consistent with previous quasar lifetime studies, it poses significant challenges on the current model for the growth of supermassive black holes located in the center of the quasars' host galaxies, which requires that quasar lifetimes are more than an order of magnitude longer.

Keywords: Supermassive black holes, Early universe, Quasars, Astronomy data analysis, High-redshift galaxies
Modeling the Galactic Neutron Star Population for Use in Continuous Gravitational-wave Searches. Searches for continuous gravitational waves (GW) from unknown Galactic neutron stars provide limits on the shapes of neutron stars. A rotating neutron star will produce GW if asymmetric deformations exist in its structure that are characterized by the star's ellipticity. In this study, we use a simple model of the spatial and spin distribution of Galactic neutron stars to estimate the total number of neutron stars probed, using GW, to a given upper limit on the ellipticity. This may help optimize future searches with improved sensitivity. The improved sensitivity of third-generation GW detectors may increase the number of neutron stars probed, to a given ellipticity, by factors of 100 to 1000.

Keywords: Neutron stars, Gravitational waves
Close Stellar Flybys Common in Low-mass Clusters. Numerous protoplanetary disks show distinct spiral arms features. While possibly caused by a range of processes, detailed pattern analysis points at close stellar flybys as cause for some of them. Surprisingly, these disks reside in young low-mass clusters, where close stellar flybys are expected to be rare. This fact motivated us to take a fresh look at the frequency of close flybys in low-mass clusters. In the solar neighborhood, low-mass clusters have smaller half-mass radii than their more massive counterparts. We show that this observational fact results in the mean and central stellar density of low-mass clusters being approximately the same as in high-mass clusters, which is rarely reflected in theoretical studies. We perform N-body simulations of the stellar dynamics in young clusters obeying the observed mass-radius relation. Taking the mean disk truncation radius as a proxy for the degree of influence of the environment, we find that the influence of the environment on disks is more or less the same in low- and high-mass clusters. Even the fraction of small disks (&lt;10 au) is nearly identical. Our main conclusion is that the frequency of close flybys seems to have been severely underestimated for low-mass clusters. A testable prediction of this hypothesis is that low-mass clusters should contain 10%-15% of disks smaller than 30 au truncated by flybys. These truncated disks should be distinguishable from primordially small disks by their steep outer edge.

Keywords: Young star clusters, Circumstellar disks
Catastrophic Cooling in Superwinds. II. Exploring the Parameter Space. Superwinds and superbubbles driven by mechanical feedback from super star clusters (SSCs) are common features in many star-forming galaxies. While the adiabatic fluid model can well describe the dynamics of superwinds, several observations of starburst galaxies revealed the presence of compact regions with suppressed superwinds and strongly radiative cooling, i.e., catastrophic cooling. In the present study, we employ the nonequilibrium atomic chemistry and cooling package MAIHEM, built on the FLASH hydrodynamics code, to generate a grid of models investigating the dependence of cooling modes on the metallicity, SSC outflow parameters, and ambient density. While gas metallicity plays a substantial role, catastrophic cooling is more sensitive to high mass loading and reduced kinetic heating efficiency. Our hydrodynamic simulations indicate that the presence of a hot superbubble does not necessarily imply an adiabatic outflow and vice versa. Using CLOUDY photoionization models, we predict UV and optical line emission for both adiabatic and catastrophic cooling outflows, for radiation-bounded and partially density-bounded models. Although the line ratios predicted by our radiation-bounded models agree well with observations of star-forming galaxies, they do not provide diagnostics that unambiguously distinguish the parameter space of catastrophically cooling flows. Comparison with observations suggests the possibility of minor density bounding, nonequilibrium ionization, and/or observational bias toward the central outflow regions.

Keywords: Starburst galaxies, Cooling flows, Star forming regions, Superclusters, Emission line galaxies, Lyman-alpha galaxies, Lyman-break galaxies, H II regions, Superbubbles
Emission of Magnetar Bursts and Precursors of Neutron Star Mergers. Magnetar bursts can be emitted by Alfvén waves growing in the outer magnetosphere to nonlinear amplitudes, δB/ B ~ 1, and triggering magnetic reconnection. Similar magnetic flares should occur quasi-periodically in a magnetized neutron star binary nearing merger. In both cases, fast dissipation in the magnetic flare creates optically thick e± plasma, whose heat capacity is negligible compared with the generated radiation energy. Magnetic dissipation then involves photon viscosity and acts through Compton drag on the plasma bulk motions in the reconnection region. The effective temperature of the resulting Comptonization process is self-regulated to tens of keV. The generated X-ray emission is calculated using time-dependent radiative transfer simulations, which follow the creation of e± pairs and the production, Comptonization, and escape of photons. The simulations show how the dissipation region becomes dressed in an e± coat and how the escaping spectrum is shaped by radiative transfer through the coat. The results are compared with observed magnetar bursts, including the recent activity of SGR 1935+2154 accompanied by a fast radio burst. Predictions are made for X-ray precursors of magnetized neutron star mergers.

Keywords: Neutron stars, Plasma astrophysics, X-ray transient sources, Radio bursts, Radiative transfer, Radiative processes, Magnetars
Solar Origin of Bare Ion Anomalies in the Solar Wind and Interplanetary Coronal Mass Ejections. Previous studies of the solar wind and interplanetary coronal mass ejections (ICMEs) have shown periods throughout solar cycle 23 when heliospheric measurements of ion composition appear anomalous. In these cases, C6+ and other bare ion densities, i.e., fully stripped ions, are unusually low, leading it to be classified as the Outlier solar wind. However, its origin and solar source(s) remain largely uncertain. In this work, we further characterize the Outlier wind to connect its heliospheric structure to its solar source to constrain the conditions of its formation. Through an analysis of the plasma and magnetic field properties of each occurrence between 1998 and 2011, we find that the Outlier plasma occurs in the slow solar wind or interplanetary mass ejections (~460 km s-1), and comprises distinct, high density events lasting less than 10 hr. The number of events is correlated with the solar cycle, indicating the process leading to the depletion of bare ions is strongly governed by the magnetic field. Additionally, the events exhibit a bi- or unidirectional suprathermal electron strahl that is concurrent with changes in the magnetic field direction. Moreover, the Outlier wind's composition, entropy, Alfvén speed, and proton temperature suggest a helmet streamer or active region origin. Together, the properties exhibited by the Outlier wind suggest a strong connection to the heliospheric current sheet and that the solar wind events are smaller scale versions of those seen in ICMEs, such as small magnetic flux ropes. However, more work is necessary to determine the source and creation process in the vicinity of the Sun.

Keywords: Slow solar wind, The Sun, Solar abundances, Solar physics, Interplanetary physics