Sazuna/UAT_keywords huggingface dataset:
Rotating Solar Models in Agreement with Helioseismic Results and Updated Neutrino Fluxes. Standard solar models (SSMs) constructed in accordance with old solar abundances are in reasonable agreement with seismically inferred results, but SSMs with new low-metal abundances disagree with the seismically inferred results. The constraints of neutrino fluxes on solar models exist in parallel with those of helioseismic results. The solar neutrino fluxes were updated by the Borexino Collaboration. We constructed rotating solar models with new low-metal abundances where the effects of enhanced diffusion and convection overshoot were included. A rotating model using OPAL opacities and the Caffau abundance scale has better sound-speed and density profiles than the SSM with the old solar abundances and reproduces the observed p-mode frequency ratios r 02 and r 13. The depth and helium abundance of the convection zone of the model agree with the seismically inferred ones at the level of 1σ. The updated neutrino fluxes are also reproduced by the model at the level of 1σ. The effects of rotation and enhanced diffusion not only improve the model's sound-speed and density profiles but also bring the neutrino fluxes predicted by the model into agreement with the detected ones. Moreover, the calculations show that OP may underestimate opacities for the regions of the Sun with T ≳ 5 × 106 K by around 1.5%, while OPAL may underestimate opacities for the regions of the Sun with 2 × 106 K ≲ T ≲ 5 × 106 K by about 1%-2%.

Keywords: Solar rotation, Solar interior, Helioseismology, Solar neutrinos, Solar abundances
On the X-Ray, Optical, and Radio Afterglows of the BdHN I GRB 180720B Generated by Synchrotron Emission. Gamma-ray bursts (GRBs) are systems of unprecedented complexity across all the electromagnetic spectrum, including the radio, optical, X-rays, gamma rays in the MeV and GeV regimes, as well as ultrahigh-energy cosmic rays, each manifested in seven specific physical processes with widely different characteristic evolution timescales ranging from 10-14 s to 107 s or longer. We here study the long GRB 180720B originating from a binary system composed of a massive carbon-oxygen (CO) star of about 10M ⊙ and a companion neutron star (NS). The gravitational collapse of the CO star gives rise to a spinning newborn NS (νNS), with an initial period of P 0 = 1 ms that powers the synchrotron radiation in the radio, optical, and X-ray wavelengths. We here investigate solely the GRB 180720B afterglows and present a detailed treatment of its origin based on the synchrotron radiation released by the interaction of the νNS and the SN ejecta. We show that in parallel to the X-ray afterglow, the spinning νNS also powers the optical and radio afterglows and allows to infer the νNS and ejecta parameters that fit the observational data.

Keywords: Gamma-ray bursts
Verification of the Standard Theory of Plasma Emission with Particle-in-cell Simulations. The standard theory of plasma emission is based on kinetic couplings between a single beam of energetic electrons and unmagnetized thermal plasmas, involving multistep nonlinear wave-particle and wave-wave interactions. The theory has not yet been completely verified with fully kinetic electromagnetic particle-in-cell (PIC) simulations. Earlier studies, greatly limited by available computational resources, are controversial regarding whether the fundamental emission can be generated according to the standard theory. To resolve the controversy, we conducted PIC simulations with a large domain of simulations and a large number of macroparticles, among the largest ones of similar studies. We found significant fundamental emission if the relative beam density is small enough (say, ≤0.01), in line with an earlier study with a much smaller domain; the relative intensity (normalized by the total initial beam energy) of all modes, except the mode associated with the beam-electromagnetic Weibel instability, decreases with the increasing relative density of the beam. We also found a significant transverse magnetic component associated with the superluminal Langmuir turbulence, which has been mistakenly regarded as evidence of the F emission in the earlier study. Further investigations are required to reveal their origin.

Keywords: Solar coronal radio emission, Plasma astrophysics, Radio bursts, Solar corona, Solar activity
Deep-learning Reconstruction of Sunspot Vector Magnetic Fields for Forecasting Solar Storms. Solar magnetic activity produces extreme solar flares and coronal mass ejections, which pose grave threats to electronic infrastructure and can significantly disrupt economic activity. It is therefore important to appreciate the triggers of explosive solar activity and develop reliable space weather forecasting. Photospheric vector magnetic field data capture sunspot magnetic field complexity and can therefore improve the quality of space weather prediction. However, state-of-the-art vector field observations are consistently only available from Solar Dynamics Observatory/Helioseismic and Magnetic Imager (HMI) since 2010, with most other current and past missions and observational facilities, such as Global Oscillations Network Group (GONG), only recording line-of-sight (LOS) fields. Here, using an inception-based convolutional neural network (CNN), we reconstruct HMI sunspot vector field features from LOS magnetograms of HMI and GONG with high fidelity (~90% correlation) and sustained flare forecasting accuracy. We rebuild vector field features during the 2003 Halloween storms, for which only LOS field observations are available, and the CNN-estimated electric current helicity accurately captures the observed rotation of the associated sunspot prior to the extreme flares, showing a striking increase. Our study thus paves the way for reconstructing three solar cycles worth of vector field data from past LOS measurements, which are of great utility in improving space weather forecasting models and gaining new insights about solar activity.

Keywords: Solar activity, Solar active region magnetic fields
Effective Inspiral Spin Distribution of Primordial Black Hole Binaries. We investigate the probability distribution of the effective inspiral spin, the mass ratio, and the chirp mass of primordial black hole (PBH) binaries, incorporating the effect of the critical phenomena of gravitational collapse. As a leading order estimation, each binary is assumed to be formed from two PBHs that are randomly chosen according to the probability distribution of single PBHs, and the accretion effects on the mass and spin of each PBH are not considered for simplicity. We find that, although the critical phenomena can lead to large spins on the low-mass tail, the effective inspiral spin of the binary is statistically very small, $\sqrt{{\unicode{x02329}}{{\chi }}_{{\rm{e}}{\rm{f}}{\rm{f}}}^{2}{\unicode{x0232A}}}\sim {10}^{-3}$ . We also see that there is almost no anticorrelation between the effective inspiral spin and the mass ratio, which can be inferred from observations.

Keywords: Cosmology, Black holes
Inferring Line-of-sight Velocities and Doppler Widths from Stokes Profiles of GST/NIRIS Using Stacked Deep Neural Networks. Obtaining high-quality magnetic and velocity fields through Stokes inversion is crucial in solar physics. In this paper, we present a new deep learning method, named Stacked Deep Neural Networks (SDNN), for inferring line-of-sight (LOS) velocities and Doppler widths from Stokes profiles collected by the Near InfraRed Imaging Spectropolarimeter (NIRIS) on the 1.6 m Goode Solar Telescope (GST) at the Big Bear Solar Observatory (BBSO). The training data for SDNN are prepared by a Milne-Eddington (ME) inversion code used by BBSO. We quantitatively assess SDNN, comparing its inversion results with those obtained by the ME inversion code and related machine-learning (ML) algorithms such as multiple support vector regression, multilayer perceptrons, and a pixel-level convolutional neural network. Major findings from our experimental study are summarized as follows. First, the SDNN-inferred LOS velocities are highly correlated to the ME-calculated ones with the Pearson product-moment correlation coefficient being close to 0.9 on average. Second, SDNN is faster, while producing smoother and cleaner LOS velocity and Doppler width maps, than the ME inversion code. Third, the maps produced by SDNN are closer to ME's maps than those from the related ML algorithms, demonstrating that the learning capability of SDNN is better than those of the ML algorithms. Finally, a comparison between the inversion results of ME and SDNN based on GST/NIRIS and those from the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory in flare-prolific active region NOAA 12673 is presented. We also discuss extensions of SDNN for inferring vector magnetic fields with empirical evaluation.

Keywords: Solar atmosphere, Convolutional neural networks, Solar magnetic fields
A Generalized Analytical Model for Thermal and Bulk Comptonization in Accretion-powered X-Ray Pulsars. We develop a new theoretical model describing the formation of the radiation spectrum in accretion-powered X-ray pulsars as a result of bulk and thermal Comptonization of photons in the accretion column. The new model extends the previous model developed by the authors in four ways: (1) we utilize a conical rather than cylindrical geometry; (2) the radiation components emitted from the column wall and the column top are computed separately; (3) the model allows for a nonzero impact velocity at the stellar surface; and (4) the velocity profile of the gas merges with Newtonian freefall far from the star. We show that these extensions allow the new model to simulate sources over a wide range of accretion rates. The model is based on a rigorous mathematical approach in which we obtain an exact series solution for the Green's function describing the reprocessing of monochromatic seed photons. Emergent spectra are then computed by convolving the Green's function with bremsstrahlung, cyclotron, and blackbody photon sources. The range of the new model is demonstrated via applications to the high-luminosity source Her X-1, and the low-luminosity source X Per. The new model suggests that the observed increase in spectral hardness associated with increasing luminosity in Her X-1 may be due to a decrease in the surface impact velocity, which increases the PdV work done on the radiation field by the gas.

Keywords: Neutron stars, X-ray binary stars, Radiative processes
Measuring the Orbits of the Arches and Quintuplet Clusters Using HST and Gaia: Exploring Scenarios for Star Formation near the Galactic Center. We present new absolute proper-motion measurements for the Arches and Quintuplet clusters, two young massive star clusters near the Galactic center. Using multiepoch HST observations, we construct proper-motion catalogs for the Arches (~35,000 stars) and Quintuplet (~40,000 stars) fields in ICRF coordinates established using stars in common with the Gaia EDR3 catalog. The bulk proper motions of the clusters are measured to be (μ  α*, μ  δ ) = (-0.80 ± 0.032, -1.89 ± 0.021) mas yr-1 for the Arches and (μ  α*, μ  δ ) = (-0.96 ± 0.032, -2.29 ± 0.023) mas yr-1 for the Quintuplet, achieving ≳5× higher precision than past measurements. We place the first constraints on the properties of the cluster orbits that incorporate the uncertainty in their current line-of-sight distances. The clusters will not approach closer than ~25 pc to Sgr A*, making it unlikely that they will inspiral into the nuclear star cluster within their lifetime. Further, the cluster orbits are not consistent with being circular; the average value of r apo/r peri is ~1.9 (equivalent to an eccentricity of ~0.31) for both clusters. Lastly, we find that the clusters do not share a common orbit, challenging one proposed formation scenario in which the clusters formed from molecular clouds on the open stream orbit derived by Kruijssen et al. Meanwhile, our constraints on the birth location and velocity of the clusters offer mild support for a scenario in which the clusters formed via collisions between gas clouds on the x 1 and x 2 bar orbit families.

Keywords: Star formation, Galactic center, Young star clusters, Astrometry
The Effect of Primordial Black Holes and Streaming Motions on Structure Formation. Primordial black holes could be an important component of the dark matter in the universe. If they exist, they would add a Poisson component to the matter power spectrum. The extra power would speed up the emergence of dark matter halos that seed the formation of first stars and galaxies. Kashlinsky suggested that the additional velocity fluctuations would accelerate the infall of baryons onto the dark matter potential wells. We analyze the effect of primordial black holes on the baryon infall from recombination to reionization and find the correction to be a few percent of the power suppression first identified by Tseliakhovich &amp; Hirata. However, the dynamical effect of this correction in addition to the extra power speeds up the formation of halos in the mass range of 104-105-6 M ⊙, while slightly decreasing the formation of those in the range 106-108 M ⊙, confirming earlier analytic estimates and recent results of numerical simulations.

Keywords: Population III stars, Dark matter, Primordial black holes
A Quarter Century of Guitar Nebula/Filament Evolution. We have collected a new deep Chandra X-Ray Observatory exposure of PSR B2224+65 and the "Guitar Nebula," mapping the complex X-ray structure. This is accompanied by a new Hubble Space Telescope (HST) Hα image of the head of the Guitar. Comparing the HST and Chandra structures in four epochs over 25 yr, we constrain the evolution of the TeV particles that light up the filament. Cross-field diffusion appears to be enhanced, likely by the injected particles, behind the filament's sharp leading edge, explaining the filament width and its evolving surface brightness profile.

Keywords: Neutron stars, H alpha photometry, X-ray astronomy, Stellar bow shocks
Stars Crushed by Black Holes. III. Mild Compression of Radiative Stars by Supermassive Black Holes. A tidal disruption event (TDE) occurs when the gravitational field of a supermassive black hole (SMBH) destroys a star. For TDEs in which the star enters deep within the tidal radius, such that the ratio of the tidal radius to the pericenter distance β satisfies β ≫ 1, the star is tidally compressed and heated. It was predicted that the maximum density and temperature attained during deep TDEs scale as ∝ β 3 and ∝ β 2, respectively, and nuclear detonation is triggered by β ≳ 5, but these predictions have been debated over the last four decades. We perform Newtonian smoothed-particle hydrodynamics simulations of deep TDEs between a Sun-like star and a 106 M ⊙ SMBH for 2 ≤ β ≤ 10. We find that neither the maximum density nor temperature follow the ∝ β 3 and ∝ β 2 scalings or, for that matter, any power-law dependence, and that the maximum-achieved density and temperature are reduced by ~1 order of magnitude compared to past predictions. We also perform simulations in the Schwarzschild metric and find that relativistic effects modestly increase the maximum density (by a factor of ≲1.5) and induce a time lag relative to the Newtonian simulations, which is induced by time dilation. We also confirm that the time the star spends at high density and temperature is a very small fraction of its dynamical time. We therefore predict that the amount of nuclear burning achieved by radiative stars during deep TDEs is minimal.

Keywords: Black hole physics, Hydrodynamical simulations, Supermassive black holes, Hydrodynamics, Tidal disruption, Astrophysical black holes
Informed Systematic Method to Identify Variable Mid- and Late-T Dwarfs. The majority of brown dwarfs show some level of photometric or spectrophotometric variability in different wavelength ranges. This variability allow us to trace the 3D atmospheric structures of variable brown dwarfs and directly-imaged exoplanets with radiative-transfer models and mapping codes. Nevertheless, to date, we do not have an informed method to preselect the brown dwarfs that might show a higher variability amplitude for a thorough variability study. In this work, we designed and tested near-infrared spectral indices to preselect the most likely variable mid- and late-T dwarfs, which overlap in effective temperatures with directly-imaged exoplanets. We used time-resolved near-infrared Hubble Space Telescope Wide Field Camera 3 spectra of a T6.5 dwarf, 2MASS J22282889-431026, to design our novel spectral indices. We tested these spectral indices on 26 T5.5-T7.5 near-infrared SpeX/IRTF spectra, and we provided eight new mid- and late-T variable candidates. We estimated the variability fraction of our sample as ${38}_{-30}^{+4}$ %, which agrees with the variability fractions provided by Metchev for mid- to late-T dwarfs. In addition, two of the three previously known variables in our sample of SpeX spectra are flagged as variable candidates by our indices. Similarly, all seven known nonvariables in our sample are flagged as nonvariable objects by our indices. These results suggest that our spectral indices might be used to find variable mid- and late-T brown dwarf variables. These indices may be crucial in the future to select cool directly-imaged exoplanets for variability studies.

Keywords: Spectral index, Brown dwarfs, Atmospheric variability, T dwarfs
A Machine Learning Framework to Predict Images of Edge-on Protoplanetary Disks. The physical structure and properties of protoplanetary disks are typically derived from spatially resolved disk images. Edge-on disks in particular provide an important view point on the vertical structure and degree of settling of disks. Such analyses rely on radiative transfer (RT) calculations that are generally computationally intensive due to the high optical depth of disks. Here we present a machine learning framework that has the potential to dramatically speed up the forward modeling process by approximating the results of RT calculations. This framework, trained on an initial set of RT calculations, utilizes an autoencoder neural network to enable the generation of synthetic scattered light images of edge-on disks directly from a set of physical parameters. We demonstrate that this framework generates synthetic images 2-3 orders of magnitude faster than using RT calculations. These machine learning-generated images appear to approximate the RT images well, in particular preserving their size and shape. We also find a strong correlation between the latent space representations of the generated disk images and several of their associated physical parameters. Finally, we discuss potential changes to the framework, such as methods to further improve the image quality, extending the framework to multiple wavelengths, and inverting the process to infer physical parameters from observed images. Overall, these new tools have the potential to enable a more efficient and uniform analysis of edge-on disk properties and the initial conditions of planet formation.

Keywords: Pre-main sequence stars, Radiative transfer
Tracing the Giant Outer Halo of the Mysterious Massive Disk Galaxy M104. I. Photometry of the Extended Globular Cluster Systems. M104 (NGC 4594, the Sombrero galaxy) is a mysterious massive early-type galaxy that shows a dominant bulge and a prominent disk. However, the presence of a halo in M104 has been elusive, and it is not yet known how M104 has acquired such a peculiar structure. Using wide (~2 deg2) and deep ugi images of M104 obtained with the CFHT/MegaCam, we detect a large number of globular clusters (GCs) found out to $R\approx 35^{\prime} $ (~100 kpc). The color distribution of these GCs shows two subpopulations: a blue (metal-poor) system and a red (metal-rich) system. The total number of GCs is estimated to be N GC = 1610 ± 30 and the specific frequency to be S  N  = 1.8 ± 0.1. The radial number density profile of the GCs is steep in the inner region at $R\lt 20^{\prime} $ and becomes shallow in the outer region at $20^{\prime} \lt R\lt 35^{\prime} $ . The outer region is dominated by blue GCs and is extended out to $R\approx 35^{\prime} $ . This shows clearly the existence of a giant metal-poor halo in M104. The inner region is composed of a bulge hosting a disk, corresponding to a metal-rich halo as seen in early-type galaxies. At least two clumps of blue GCs are found in the outer region. One clump is overlapped with a faint stellar stream located in the southwest, indicating that it may be a remnant of a disrupted dwarf galaxy. Our results imply that the metal-rich inner halo of M104 formed first via major mergers, and the metal-poor outer halo grew via numerous minor mergers.

Keywords: Globular star clusters, Lenticular galaxies, Galaxy evolution, Elliptical galaxies, Early-type galaxies
Interstellar Scintillation and Polarization of PSR B0656+14 in the Monogem Ring. High-sensitivity interstellar scintillation and polarization observations of PSR B0656+14 made at three epochs over a year using the Five-hundred-meter Aperture Spherical radio Telescope (FAST) show that the scattering is dominated by two different compact regions. We identify the one nearer to the pulsar with the shell of the Monogem Ring, thereby confirming the association. The other is probably associated with the Local Bubble. We find that the observed position angles of the pulsar spin axis and the spatial velocity are significantly different, with a separation of 19.°3 ± 0.°8, inconsistent with a previously published near-perfect alignment of 1° ± 2°. The two independent scattering regions are clearly defined in the secondary spectra, which show two strong forward parabolic arcs. The arc curvatures imply that the scattering screens corresponding to the outer and inner arcs are located approximately 28 pc from PSR B0656+14 and 185 pc from the Earth, respectively. Comparison of the observed Doppler profiles with electromagnetic simulations shows that both scattering regions are mildly anisotropic. For the outer arc, we estimate the anisotropy A  R  to be approximately 1.3, with the scattering irregularities aligned parallel to the pulsar velocity. For the outer arc, we compare the observed delay profiles with delay profiles computed from a theoretical strong-scattering model. Our results suggest that the spatial spectrum of the scattering irregularities in the Monogem Ring is flatter than Kolmogorov, but further observations are required to confirm this.

Keywords: Interstellar medium, Pulsars