Sazuna/UAT_keywords huggingface dataset:
Critical Balance and the Physics of Magnetohydrodynamic Turbulence. A discussion of the advantages and limitations of the concept of critical balance (CB), as employed in turbulence phenomenologies, is presented. The incompressible magnetohydrodynamic (MHD) case is a particular focus. The discussion emphasizes the status of the original Goldreich &amp; Sridhar CB conjecture relative to related theoretical issues and models in an MHD description of plasma turbulence. Issues examined include variance and spectral anisotropy, influence of a mean magnetic field, local and nonlocal effects, and the potential for effects of external driving. Related models such as Reduced MHD provide a valuable context in the considerations. Some new results concerning spectral features and timescales are presented in the course of the discussion. Also mentioned briefly are some adaptations and variations of CB.

Keywords: Space plasmas, Magnetohydrodynamics, Interplanetary turbulence, Solar wind, Alfven waves, Spectral energy distribution
Sensitivity Kernels for Inferring Lorentz Stresses from Normal-mode Frequency Splittings in the Sun. Departures from standard spherically symmetric solar models, in the form of perturbations such as global and local-scale flows and structural asphericities, result in the splitting of eigenfrequencies in the observed spectrum of solar oscillations. Drawing from prevalent ideas in normal-mode-coupling theory in geophysical literature, we devise a procedure that enables the computation of sensitivity kernels for general Lorentz-stress fields in the Sun. Mode coupling due to any perturbation requires careful consideration of self- and cross coupling of multiplets. Invoking the isolated-multiplet approximation allows for limiting the treatment to purely self coupling, requiring significantly less computational resources. We identify the presence of such isolated multiplets under the effect of Lorentz stresses in the Sun. Currently, solar missions allow for precise measurements of self coupling of multiplets via "a-coefficients" and the cross-spectral correlation signal that enables the estimation of the "structure coefficients". We demonstrate the forward problem for both self coupling (a-coefficients) and cross coupling (structure coefficients). In doing so, we plot the self-coupling kernels and estimate a-coefficients arising from a combination of deep-toroidal and surface-dipolar axisymmetric fields. We also compute the structure coefficients for an arbitrary general magnetic field (real and solenoidal) and plot the corresponding "splitting function", a convenient way to visualize the splitting of multiplets under 3D internal perturbations. The results discussed in this paper pave the way to formally pose an inverse problem and infer solar internal magnetic fields.

Keywords: Magnetohydrodynamics, Solar interior, Helioseismology, Solar physics, Solar magnetic fields, Asteroseismology
A Blueprint for the Milky Way's Stellar Populations: The Power of Large Photometric and Astrometric Surveys. Recent advances from astronomical surveys have revealed spatial, chemical, and kinematical inhomogeneities in the inner region of the stellar halo of the Milky Way. In particular, large spectroscopic surveys, combined with Gaia astrometric data, have provided powerful tools for analyzing the detailed abundances and accurate kinematics for individual stars. Despite these noteworthy efforts, however, spectroscopic samples are typically limited by the numbers of stars considered; their analysis and interpretation are also hampered by the complex selection functions that are often employed. Here we present a powerful alternative approach—a synoptic view of the spatial, chemical, and kinematical distributions of stars in the Milky Way based on large photometric survey databases, enabled by a well-calibrated technique for obtaining individual stellar metal abundances from broadband photometry. We combine metallicities with accurate proper motions from the Gaia mission along the prime meridian of the Galaxy, and find that various stellar components are clearly separated from each other in the metallicity versus rotation-velocity space. The observed metallicity distribution of the inner-halo stars deviates from the traditional single-peaked distribution, and exhibits complex substructures comprising varying contributions from individual stellar populations, sometimes with striking double peaks at low metallicities. The substructures revealed from our less-biased, comprehensive maps demonstrate the clear advantages of this approach, which can be built upon by future multiband photometric surveys, and used as a blueprint for identifying the stars of greatest interest for upcoming spectroscopic studies.

Keywords: Milky Way formation, Surveys, Stellar abundances, Stellar populations, Galaxy structure, Milky Way dynamics, Galaxy stellar content, Milky Way disk, Milky Way stellar halo, Galactic abundances, Milky Way Galaxy
The Lyman Continuum Escape Fraction of Galaxies and AGN in the GOODS Fields. We present our analysis of the Lyman continuum (LyC) emission and escape fraction of 111 spectroscopically verified galaxies with and without active galactic nuclei (AGN) from 2.26 &lt; z &lt; 4.3. We extended our ERS sample from Smith et al. with 64 galaxies in the GOODS North and South fields using WFC3/UVIS F225W, F275W, and F336W mosaics we independently drizzled using the HDUV, CANDELS, and UVUDF data. Among the 17 AGN from the 111 galaxies, one provided a LyC detection in F275W at ${m}_{\mathrm{AB}}$ = 23.19 mag (signal-to-noise ratio, S/N, ≃ 133) and GALEX NUV at ${m}_{\mathrm{AB}}$ = 23.77 mag (S/N ≃ 13). We simultaneously fit SDSS and Chandra spectra of this AGN to an accretion disk and Comptonization model, and find ${f}_{\mathrm{esc}}$ values of ${f}_{\mathrm{esc}}^{{\rm{F}}275{\rm{W}}}\simeq {28}_{-4}^{+20} \% $ and ${f}_{\mathrm{esc}}^{\mathrm{NUV}}\simeq {30}_{-5}^{+22} \% $ . For the remaining 110 galaxies, we stack image cutouts that capture their LyC emission using the F225W, F275W, and F336W data of the GOODS and ERS samples, and both combined, as well as subsamples of galaxies with and without AGN, and all galaxies. We find the stack of 17 AGN dominate the LyC production from $\langle z\rangle $ ≃ 2.3-4.3 by a factor of ∼10 compared to all 94 galaxies without AGN. While the IGM of the early universe may have been reionized mostly by massive stars, there is evidence that a significant portion of the ionizing energy came from AGN.

Keywords: Ultraviolet astronomy, Active galactic nuclei, High-redshift galaxies, Reionization
Long-term Near-infrared Brightening of Nonvariable OH/IR Stars. Nonvariable OH/IR stars are thought to have just left the asymptotic giant branch (AGB) phase. In this conventional picture, they must still show strong circumstellar extinction caused by the dust ejected during the AGB phase, and the extinction is expected to decrease over time because of the dispersal of the circumstellar dust after the cessation of stellar mass loss. The reduction of extinction makes the stars become apparently brighter and bluer with time, especially in the near-infrared (NIR) range. We look for such long-term brightening of nonvariable OH/IR stars by using 2MASS, UKIDSS, and OAOWFC survey data. As such, we obtain multiepoch NIR data taken over a 20 yr period (1997-2017) for 6 of 16 nonvariable OH/IR stars, and all 6 objects are found to be brightening. The K-band brightening rate of five objects ranges from 0.010 to 0.130 mag yr-1, which is reasonably explained with the conventional picture. However, one OH/IR star, OH 31.0-0.2, shows a rapid brightening, which cannot be explained only by the dispersal of the dust shell. Multicolor (J-, H-, and K-band) data are obtained for three objects, OH 25.1-0.3, OH 53.6-0.2, and OH 77.9+0.2. Surprisingly, none of them appears to have become bluer, and OH 53.6-0.2 is found to have reddened at a rate of 0.013 mag yr-1 in (J - K). Our findings suggest other mechanisms such as rapid changes in stellar properties (temperature or luminosity) or a generation of a new batch of dust grains.

Keywords: Post-asymptotic giant branch stars, Late-type stars, Stellar mass loss, Circumstellar matter, Asymptotic giant branch stars, Stellar evolution
Neutrino Transport with Monte Carlo Method. I. Toward Fully Consistent Implementation of Nucleon Recoils in Core-collapse Supernova Simulations. The small energy exchange via nucleon recoils in neutrino-nucleon scattering is now supposed to be one of the important factors for successful explosions of core-collapse supernovae (CCSNe), as they can change neutrino spectra through accumulation of a large number of scatterings. In deterministic methods employed for neutrino transport in CCSN simulations, we normally cannot afford to deploy a large enough number of energy bins needed to resolve this small energy exchange, and subgrid techniques are employed one way or another. In this paper, we study quantitatively with the Monte Carlo (MC) method how well such a treatment performs. We first investigate the effects of nucleon recoils on the neutrino spectra and confirm that the average energy is reduced by ∼15% for heavy-lepton neutrinos and much smaller amounts for other types of neutrinos in a typical postbounce situation. It is also observed that the nucleon scattering dominates the electron scattering in the thermalization of neutrino spectra in all flavors. We then study possible artifacts that the coarse energy grid may produce in the deterministic methods. In order to mimic the latter calculation, we redistribute MC particles in each energy bin after a certain interval in a couple of ways and study how the results are affected, depending on the energy resolution. We also discuss the possible implications of our results for the deterministic methods.

Keywords: Supernova neutrinos, Core-collapse supernovae
Selection of Massive Evolved Galaxies at 3 ≤ z ≤ 4.5 in the CANDELS Fields. Using the CANDELS photometric catalogs for the Hubble Space Telescope/ACS and WFC3, we identified massive evolved galaxies at 3 &lt; z &lt; 4.5 employing three different selection methods. We find the comoving number density of these objects to be ∼2 × 10-5 and 8 × 10-6 Mpc-3 after correction for completeness for two redshift bins centered at z = 3.4, 4.7. We quantify a measure of how much confidence we should have for each candidate galaxy from different selections and what the conservative error estimates propagated into our selection are. Then we compare the evolution of the corresponding number densities and their stellar mass density with numerical simulations, semianalytical models, and previous observational estimates, which shows slight tension at higher redshifts as the models tend to underestimate the number and mass densities. By estimating the average halo masses of the candidates (Mh ≈ 4.2, 1.9, and 1.3 × 1012 M⊙ for redshift bins centered at z = 3.4, 4.1, and 4.7), we find them to be consistent with halos that were efficient in turning baryons to stars, relatively immune to the feedback effects, and on the verge of transition into hot-mode accretion. This can suggest the relative cosmological starvation of the cold gas followed by an overconsumption phase in which the galaxy rapidly consumes the available cold gas as one of the possible drivers for the quenching of the massive evolved population at high redshift.

Keywords: Extragalactic astronomy, High-redshift galaxies, Galaxy evolution, Galaxies
Imaging the 511 keV Positron Annihilation Sky with COSI. The balloon-borne Compton Spectrometer and Imager (COSI) had a successful 46-day flight in 2016. The instrument is sensitive to photons in the energy range 0.2-5 MeV. Compton telescopes have the advantage of a unique imaging response and provide the possibility of strong background suppression. With its high-purity germanium detectors, COSI can precisely map γ-ray line emission. The strongest persistent and diffuse γ-ray line signal is the 511 keV emission line from the annihilation of electrons with positrons from the direction of the Galactic center. While many sources have been proposed to explain the amount of positrons, ${\dot{N}}_{{e}^{+}}\sim {10}^{50}\,{e}^{+}\,{\mathrm{yr}}^{-1}$ , the true contributions remain unsolved. In this study, we aim at imaging the 511 keV sky with COSI and pursue a full-forward modeling approach, using a simulated and binned imaging response. For the strong instrumental background, we describe an empirical approach to take the balloon environment into account. We perform two alternative methods to describe the signal: Richardson-Lucy deconvolution, an iterative method toward the maximum likelihood solution, and model fitting with predefined emission templates. Consistently with both methods, we find a 511 keV bulge signal with a flux between 0.9 and $3.1\times {10}^{-3}\,\mathrm{photons}\,{\mathrm{cm}}^{-2}\,{{\rm{s}}}^{-1}$ , confirming earlier measurements, and also indications of more extended emission. The upper limit we find for the 511 keV disk, $\lt 4.3\times {10}^{-3}\,\mathrm{photons}\,{\mathrm{cm}}^{-2}\,{{\rm{s}}}^{-1}$ , is consistent with previous detections. For large-scale emission with weak gradients, coded aperture mask instruments suffer from their inability to distinguish isotropic emission from instrumental background, while Compton telescopes provide a clear imaging response, independent of the true emission.

Keywords: Astronomy data modeling, High altitude balloons, Interstellar medium, Gamma-rays, Cosmic rays
Gravitational-wave Captures by Intermediate-mass Black Holes in Galactic Nuclei. Intermediate-mass black holes (IMBHs) have not been detected beyond any reasonable doubt, despite their potential role as massive seeds for quasars and sources of tidal disruption events, ultraluminous X-ray sources, dwarf galaxy feedback, and hypervelocity stars. Gravitational wave (GW) observations can help to find and confirm the existence of IMBHs. Current and upcoming detectors, such as LIGO, Virgo, KAGRA, LISA, ET, and DECIGO promise to identify the full range from stellar-mass to supermassive black holes. In this paper, we address the question of whether IMBHs can produce GWs in galactic nuclei. We consider the possibility that stellar black holes (SBHs) form bound systems and later coalesce with an IMBH through gravitational captures in the dense nucleus. We show that this mechanism is efficient for IMBH masses in the range $\sim 3\times {10}^{3}\,{M}_{\odot }$ - $2\times {10}^{4}\,{M}_{\odot }$ . We find that the typical distributions of peak frequencies and merger timescales depend mainly on the IMBH mass. In particular, the typical peak frequency is about 0.2 Hz, 0.1 Hz, 0.09 Hz, and 0.05 Hz for ${M}_{\mathrm{IMBH}}=5\times {10}^{3}\,{M}_{\odot }$ , $8\times {10}^{3}\,{M}_{\odot }$ , $1\times {10}^{4}\,{M}_{\odot }$ , and $2\times {10}^{4}\,{M}_{\odot }$ , respectively. Our results show that, at design sensitivity, both DECIGO and ET should be able to detect these IMBH-SBH mergers. Furthermore, most of the mergers will appear eccentric (e ≳ 0.1), providing an indication of their dynamical origin.

Keywords: Intermediate-mass black holes, Black hole physics, Galactic center, Gravitational wave detectors, Galaxy dynamics, Stellar dynamics, Gravitational wave sources, Galaxy nuclei, Gravitational wave astronomy, Galaxy kinematics, Gravitational waves, Astrophysical black holes
Broadband X-Ray Observation of Broad-line Radio Galaxy 3C 109. We present a study of the central engine in the broad-line radio galaxy 3C 109. To investigate the immediate surrounding of this accreting, supermassive black hole, we perform a multiepoch broadband spectral analysis of a joint NuSTAR/XMM observation (2017), an archival XMM observation (2005) and the 105 month averaged Swift-BAT data. We are able to clearly separate the spectrum into a primary continuum, neutral and ionized absorption, and a reflection component. The photon index of the primary continuum has changed since 2005 ( ${\rm{\Gamma }}={1.61}_{-0.01}^{+0.02}\to 1.54\pm 0.02$ ), while other components remain unchanged, indicative of minimal geometric changes to the central engine. We constrain the high-energy cutoff of 3C 109 (E ${}_{\mathrm{cut}}={49}_{-5}^{+7}$ keV ) for the first time. The reflector is found to be ionized (log ξ = ${2.3}_{-0.2}^{+0.1}$ ) but no relativistic blurring is required by the data. Spectral energy distribution (SED) analysis confirms the super-Eddington nature of 3C 109 initially (λEdd &gt; 2.09). However, we do not find any evidence for strong reflection (R = ${0.18}_{-0.03}^{+0.04}$ ) or a steep power-law index, as expected from a super-Eddington source. This puts the existing virial mass estimate of 2 ×108M☉ into question. We explore additional ways of estimating the Eddington ratio, some of which we find to be inconsistent with our initial SED estimate. We obtain a new black hole mass estimate of 9.3 ×108M☉, which brings all Eddington ratio estimates into agreement and does not require 3C 109 to be super-Eddington.

Keywords: High-luminosity active galactic nuclei, X-ray active galactic nuclei, Radio jets
Properties of Galactic B[e] Supergiants. V. 3 Pup-Constraining the Orbital Parameters and Modeling the Circumstellar Environments. We report the results of long-term spectroscopic monitoring of the A-type supergiant with the B[e] phenomenon 3 Pup = HD 62623. We confirm earlier findings that it is a binary system. The orbital parameters were derived using cross-correlation of the spectra in a range of 4460-4632 Å, which contains over 30 absorption lines. The orbit was found to be circular with a period of 137.4 ± 0.1 days, radial velocity semiamplitude K1 = 5.0 ± 0.8 km s-1, systemic radial velocity γ = +26.4 ± 2.0 km s-1, and mass function $f(m)=({1.81}_{-0.76}^{+0.97})\times {10}^{-3}$ M⊙. The object may have evolved from a pair with initial masses of ∼6.0 ${M}_{\odot }$ and ∼3.6 M⊙ with an initial orbital period of ∼5 days. Based on the fundamental parameters of the A-supergiant (luminosity log L/L⊙ = 4.1 ± 0.1 and effective temperature Teff = 8500 ± 500 K) and evolutionary tracks of mass-transferring binaries, we found current masses of the gainer M2 = 8.8 ± 0.5 M⊙ and donor M1 = 0.75 ± 0.25 M⊙. We also modeled the object's IR-excess and derived a dust mass of ∼5 × 10-5 M⊙ in the optically thin dusty disk. The orbital parameters and properties of the Hα line profile suggest that the circumstellar gaseous disk is predominantly circumbinary. The relatively low mass of the gainer led us to a suggestion that 3 Pup should be excluded from the B[e] supergiant group and moved to the FS CMa group. Overall these results further support our original suggestion that FS CMa objects are binary systems, where an earlier mass transfer caused formation of the circumstellar envelope.

Keywords: High resolution spectroscopy, Binary stars, Emission line stars
An Observational Test of Solar Plasma Heating by Magnetic Flux Cancellation. Recent observations suggest that magnetic flux cancellation may play a crucial role in heating the Sun's upper atmosphere (chromosphere, transition region, corona). Here, we intended to validate an analytic model for magnetic reconnection and consequent coronal heating, driven by a pair of converging and canceling magnetic flux sources of opposite polarities. For this test, we analyzed photospheric magnetic field and multiwavelength ultraviolet/extreme ultraviolet (EUV) observations of a small-scale flux cancellation event in a quiet-Sun internetwork region over a target interval of 5.2 hr. The observed cancellation event exhibits a converging motion of two opposite-polarity magnetic patches on the photosphere and redshifted Doppler velocities (downflows) therein consistently over the target interval, with a decrease in magnetic flux of both polarities at a rate of 1015 Mx s-1. Several impulsive EUV brightenings, with differential emission measure values peaked at 1.6-2.0 MK, are also observed in the shape of arcades with their two footpoints anchored in the two patches. The rate of magnetic energy released as heat at the flux cancellation region is estimated to be in the range of (0.2-1) × 1024 erg s-1 over the target interval, which can satisfy the requirement of previously reported heating rates for the quiet-Sun corona. Finally, both short-term (a few to several tens of minutes) variations and long-term (a few hours) trends in the magnetic energy release rate are clearly shown in the estimated rate of radiative energy loss of electrons at temperatures above 2.0 MK. All these observational findings support the validity of the investigated reconnection model for plasma heating in the upper solar atmosphere by flux cancellation.

Keywords: Solar photosphere, Solar magnetic reconnection, Solar ultraviolet emission, Solar extreme ultraviolet emission, Quiet sun, Solar coronal heating, Astronomy data analysis, Solar magnetic fields, Quiet solar corona
Particle Acceleration in a Shock Wave Propagating to an Inhomogeneous Medium. We investigate effects of upstream density fluctuations on the diffusive shock acceleration (DSA) by Monte Carlo simulations. The simulations show that particles are reaccelerated in the shock downstream region by a sound wave generated at the shock front. The timescale of turbulent acceleration by the sound wave is estimated. We propose a new back reaction of particles accelerated around the shock front. The accelerated particles generate the upstream density fluctuations by the Drury instability, which are converted to the downstream sound waves by the shock. The downstream sound waves modify the momentum spectrum of particles accelerated around the shock front. This new back reaction affects emission from the accelerated particles, which gives a new constraint on the acceleration efficiency of the DSA.

Keywords: Supernova remnants, Shocks, Particle astrophysics, Cosmic rays
Stellar Variability in a Forming Massive Star Cluster. We present a near-infrared (NIR) variability analysis for a 6' × 6' region, which encompasses the massive protocluster G286.21+0.17. The total sample comprises more than 5000 objects, of which 562 show signs of a circumstellar disk based on their infrared colors. The data includes Hubble Space Telescope observations taken in two epochs separated by 3 yr in the F110W and F160W bands. 363 objects (7% of the sample) exhibit NIR variability at a significant level (Stetson index &gt;1.7), and a higher variability fraction (14%) is found for the young stellar objects with disk excesses. We identified four high amplitude (&gt;0.6 mag) variables seen in both NIR bands. Follow-up and archival observations of the most variable object in this survey (G286.2032+0.1740) reveal a rising light curve over 8 yr from 2011 to 2019, with a K band brightening of 3.5 mag. Overall the temporal behavior of G286.2032+0.1740 resembles that of typical FU Ori objects; however, its pre-burst luminosity indicates it has a very low mass (&lt;0.12 M☉), making it an extreme case of an outburst event that is still ongoing.

Keywords: Accretion, Young stellar objects, Pre-main sequence stars, Variable stars, Stellar accretion disks
Orbital Modulation of Gamma Rays from PSR J2339-0533. We report on orbital modulation of the 100-600 MeV gamma-ray emission of the PB = 4.6 hr millisecond pulsar binary PSR J2339-0533 using 11 yr of Fermi Large Area Telescope data. The modulation has high significance (chance probability p ≍ 10-7), is approximately sinusoidal, peaks near pulsar superior conjunction, and is detected only in the low-energy 100-600 MeV band. The modulation is confined to the on-pulse interval, suggesting that the variation is in the 2.9 ms pulsed signal itself. This contrasts with the few other known systems exhibiting GeV orbital modulations, as these are unpulsed and generally associated with beamed emission from an intrabinary shock. The origin of the modulated pulsed signal is not yet clear, although we describe several scenarios, including Compton upscattering of photons from the heated companion. This would require high coherence in the striped pulsar wind.

Keywords: Millisecond pulsars, Gamma-ray sources, Close binary stars, Pulsars, Low-mass x-ray binary stars, Gamma-rays