Sazuna/UAT_keywords huggingface dataset:
X-Ray Spectroscopy in the Microcalorimeter Era. II. A New Diagnostic on Column Density from the Case A to B Transition in H- and He-like Iron. The Soft X-ray Spectrometer on board Hitomi, with the unprecedented resolving power of R ∼ 1250, allowed the detection of members of the Fe XXV Kα complex emission spectra from the center of the Perseus Cluster. In this paper, we introduce a novel method of measuring the column density using the optically thin (Case A) to optically thick (Case B) transition for one- and two-electron systems. We compare the Fe XXV K α line ratios computed with CLOUDY with that from the Hitomi observations in the outer region of the Perseus core using collision strengths from different atomic data sets, and obtain good agreement. We also show the effect of turbulence on Fe XXV Kα line ratios and interplay between column density and metallicity. Additionally, we discuss the atomic number dependence of transition probabilities for allowed and unallowed transitions, which causes highly charged He-like systems, such as Fe XXV, to behave fundamentally differently from He I.

Keywords: Galaxy clusters, X-ray astronomy, High resolution spectroscopy, Interstellar thermal emission, Radiative transfer, Perseus Cluster
Investigation of Coronal Properties of X-Ray Bright G-dwarf Stars Based on the Solar Surface Magnetic Field-Corona Relationship. We investigated the coronal properties of G-dwarf stars including the Sun over a wide range of X-ray luminosity LX (3 × 1026 to 2 × 1030 erg s-1). We analyzed the archival data of 10 X-ray bright (LX &gt; 1028 erg s-1) G-dwarf stars to derive their emission measure (EM) and the coronal temperature (T) during the periods when no prominent stellar flares were observed. We attempted to explain the relation on the basis of our understanding of the present Sun: a steady corona model based on the so-called Rosner-Tucker-Vaiana (RTV) scaling laws and the observed power-law distribution function of surface magnetic features. We derived a theoretical scaling law of the EM-T relation for a star with multiple active regions, and applied it to the observations combined with data in the literature. We found that with the solar parameters, our scaling law seems to be consistent with the data of slowly rotating stars. However, more X-ray-bright stars are located well above the scaling law based on the solar parameter. The scaling law may explain the observations if those stars show a power-law distribution function of active regions with the same power-law index but a 10-100 times larger coefficient. This suggests that X-ray bright stars show more active regions for a given size than the Sun. Since our samples include rapidly rotating stars, we infer that the offset of the X-ray bright stars from the present Sun-based scaling law is due to the enhancement of the surface magnetic field generation by their rapid rotation.

Keywords: Sunspot groups, Solar analogs, Stellar magnetic fields, Solar magnetic fields, Stellar coronae, X-ray stars
Low-level Carbon Monoxide Line Polarization in Two Protoplanetary Disks: HD 142527 and IM Lup. Magnetic fields are expected to play an important role in accretion processes for circumstellar disks. However, measuring the magnetic field morphology is difficult, especially when given that polarimetric (sub)millimeter continuum observations may not trace the fields in most disks. The Goldreich-Kylafis effect suggests that line polarization is perpendicular or parallel to the magnetic field direction. We attempt to observe CO(2-1), 13CO(2-1), and C18O(2-1) line polarization toward HD 142527 and IM Lup, which are large and bright protoplanetary disks. We use spatial averaging and spectral integration to search for signals in both disks, and we detect a potential CO(2-1) Stokes Q signal toward both disks. The total CO(2-1) polarization fractions are 1.57% ± 0.18% and 1.01% ± 0.10% for HD 142527 and IM Lup, respectively. Our Monte Carlo simulations indicate that these signals are marginal. We also stack Stokes parameters based on the Keplerian rotation, but no signal was found. Across the disk traced by dust of HD 142527, the 3σ upper limits for ${P}_{\mathrm{frac}}$ at 0"5 (∼80 au) resolution are typically less than 3% for CO(2-1) and 13CO(2-1) and 4% for C18O(2-1). For IM Lup the 3σ upper limits for these three lines are typically less than 3%, 4%, and 12%, respectively. Upper limits based on our stacking technique are up to a factor of ∼10 lower, although stacking areas can potentially average out small-scale polarization structure. We also compare our continuum polarization at 1.3 mm to observations at 870 μm from previous studies. The polarization in the northern dust trap of HD 142527 shows a significant change in morphology and an increase in ${P}_{\mathrm{frac}}$ as compared to 870 μm. For IM Lup, the 1.3 mm polarization may be more azimuthal and has a higher ${P}_{\mathrm{frac}}$ than at 870 μm.

Keywords: Herbig Ae/Be stars, Polarimetry, T Tauri stars, Young stellar objects, Protoplanetary disks, Circumstellar disks, Magnetic fields, Interferometry
Delayed Photons from Binary Evolution Help Reionize the Universe. High-resolution numerical simulations including feedback and aimed at calculating the escape fraction (fesc) of hydrogen-ionizing photons often assume stellar radiation based on single-stellar population synthesis models. However, strong evidence suggests the binary fraction of massive stars is ≳70%. Moreover, simulations so far have yielded values of fesc falling only on the lower end of the ∼10%-20% range, the amount presumed necessary to reionize the universe. Analyzing a high-resolution (4 pc) cosmological radiation-hydrodynamic simulation, we study how fesc changes when we include two different products of binary stellar evolution—stars stripped of their hydrogen envelopes and massive blue stragglers. Both produce significant amounts of ionizing photons 10-200 Myr after each starburst. We find the relative importance of these photons to be amplified with respect to escaped ionizing photons, because peaks in star formation rates (SFRs) and fesc are often out of phase by this 10-200 Myr. Additionally, low-mass, bursty galaxies emit Lyman continuum radiation primarily from binary products when SFRs are low. Observations of these galaxies by the James Webb Space Telescope could provide crucial information on the evolution of binary stars as a function of redshift. Overall, including stripped stars and massive blue stragglers increases our photon-weighted mean escape fraction ( $\langle {f}_{\mathrm{esc}}\rangle $ ) by ∼13% and ∼10%, respectively, resulting in $\langle {f}_{\mathrm{esc}}\rangle =17 \% $ . Our results emphasize that using updated stellar population synthesis models with binary stellar evolution provides a more sound physical basis for stellar reionization.

Keywords: Early universe, Reionization, Binary stars, Stellar evolution
Formation of Foreshock Transients and Associated Secondary Shocks. Upstream of shocks, the foreshock is filled with hot ions. When these ions are concentrated and thermalized around a discontinuity, a diamagnetic cavity bounded by compressional boundaries, referred to as a foreshock transient, forms. Sometimes, the upstream compressional boundary can further steepen into a secondary shock, which has been observed to accelerate particles and contribute to the primary shock acceleration. However, secondary shock formation conditions and processes are not fully understood. Using particle-in-cell simulations, we reveal how secondary shocks are formed. From 1D simulations, we show that electric fields play a critical role in shaping the shock's magnetic field structure, as well as in coupling the energy of hot ions to that of the shock. We demonstrate that larger thermal speed and concentration ratio of hot ions favor the formation of a secondary shock. From a more realistic 2D simulation, we examine how a discontinuity interacts with foreshock ions leading to the formation of a foreshock transient and a secondary shock. Our results imply that secondary shocks are more likely to occur at primary shocks with higher Mach number. With the secondary shock's previously proven ability to accelerate particles in cooperation with a planetary bow shock, it is even more appealing to consider them in particle acceleration of high Mach number astrophysical shocks.

Keywords: Planetary bow shocks, Space plasmas, Shocks, Plasma astrophysics
Structural Evolution in Massive Galaxies at z ∼ 2. We present 0"2 resolution Atacama Large Millimeter/submillimeter Array (ALMA) observations at 870 μm in a stellar mass-selected sample of 85 massive ( ${M}_{\star }\gt {10}^{11}\,{M}_{\odot }$ ) star-forming galaxies (SFGs) at $z=1.9\mbox{--}2.6$ in the CANDELS/3D-Hubble Space Telescope fields of UDS and GOODS-S. We measure the effective radius of the rest-frame far-infrared (FIR) emission for 62 massive SFGs. They are distributed over wide ranges of FIR size from ${R}_{{\rm{e}},\mathrm{FIR}}=0.4\,\mathrm{kpc}$ to ${R}_{{\rm{e}},\mathrm{FIR}}=6\,\mathrm{kpc}$ . The effective radius of the FIR emission is smaller by a factor of ${2.3}_{-1.0}^{+1.9}$ than the effective radius of the optical emission and is smaller by a factor of ${1.9}_{-1.0}^{+1.9}$ than the half-mass radius. Taking into account potential extended components, the FIR size would change only by ∼10%. By combining the spatial distributions of the FIR and optical emission, we investigate how galaxies change the effective radius of the optical emission and the stellar mass within a radius of 1 kpc, ${M}_{1\mathrm{kpc}}$ . The compact starburst puts most of the massive SFGs on the mass-size relation for quiescent galaxies (QGs) at z ∼ 2 within 300 Myr if the current star formation activity and its spatial distribution are maintained. We also find that within 300 Myr, ∼38% of massive SFGs can reach the central mass of ${M}_{1\mathrm{kpc}}={10}^{10.5}\,{M}_{\odot }$ , which is around the boundary between massive SFGs and QGs. These results suggest an outside-in transformation scenario in which a dense core is formed at the center of a more extended disk, likely via dissipative in-disk inflows. Synchronized observations at ALMA 870 μm and James Webb Space Telescope 3-4 μm will explicitly verify this scenario.

Keywords: Starburst galaxies, Galaxy bulges, Galaxy structure, Interstellar medium, High-redshift galaxies
To Power the X-Ray Plateaus of Gamma-Ray Bursts through Larger Amplitude Electromagnetic Waves. The origin of the gamma-ray burst (GRB) X-ray plateau, especially the internal plateau, is still unclear, but it could be related to a GRB's magnetar central engine. It is generally believed that the spin-down power of the magnetar is injected into forward external shock; however, we propose here that most of the power will be dissipated behind the GRB jet through a larger amplitude electromagnetic wave. Based on this proposal, the relevant physical conditions and observational implications are analyzed and discussed, and various kinds of X-ray light curves could be reproduced. Although the chromatic multiband afterglow in the standard external afterglow fireball model is still a matter of debate, we can naturally explain this feature through this proposal, i.e., the electrons generating the X-ray plateau and emitting the optical afterglow are accelerated by different mechanisms. It is emphasized that both the GRB jet and the spin-down wind should have significant observational consequences in the magnetar scenario, and should be focused equally in GRB physics.

Keywords: Neutron stars, Gamma-ray bursts, X-ray astronomy
On the Generation of Compressible Mirror-mode Fluctuations in the Inner Heliosheath. Measurements made with the Voyager 1 spacecraft indicate that significant levels of compressive fluctuations exist in the inner heliosheath. Some studies have already been performed with respect to the mirror-mode instability in the downstream region close to the solar wind termination shock, and here we extend the investigation to the whole inner heliosheath. We employ quasilinear theory and results from a global magnetohydrodynamic model of the heliosphere to compute the time evolution of both the temperature anisotropy and the energy density of the corresponding magnetic fluctuations, and we demonstrate their likely presence in the inner heliosheath. Furthermore, we compute the associated, locally generated density fluctuations. The results can serve as inputs for future models of the transport of compressible turbulence in the inner heliosheath.

Keywords: Interplanetary turbulence, Heliosheath, Solar wind, Heliosphere
Reaction Rate Sensitivity of the Production of γ-Ray Emitting Isotopes in Core-collapse Supernovae. Radioactive isotopes produced in core-collapse supernovae (CCSNe) provide useful insights into the underlying processes driving the collapse mechanism and the origins of elemental abundances. Their study generates a confluence of major physics research, including experimental measurements of nuclear reaction rates, astrophysical modeling, and γ-ray observations. Here we identify the key nuclear reaction rates to the nucleosynthesis of observable radioactive isotopes in explosive silicon burning during CCSNe. Using the nuclear reaction network calculator SkyNet and current REACLIB reaction rates, we evolve temperature-density-time profiles of the innermost 0.45 M⊙ ejecta from the core collapse and explosion of a 12 M⊙ star. Individually varying 3403 reaction rates by factors of 100, we identify 141 reactions that cause significant differences in the isotopes of interest, namely, 43K, 47Ca, 44,47Sc, 44Ti, 48,51Cr, 48,49V, 52,53Mn, 55,59Fe, 56,57Co, and 56,57,59Ni. For each of these reactions, we present a novel method to extract the temperature range pertinent to the nucleosynthesis of the relevant isotope; the resulting temperatures lie within the range T = 0.47-6.15 GK. Limiting the variations to within 1σ of STARLIB reaction rate uncertainties further reduces the identified reactions to 48 key rates, which can be used to guide future experimental research. Complete results are presented in tabular form.

Keywords: Explosive nucleosynthesis, Core-collapse supernovae, Nucleosynthesis, Reaction rates, Nuclear astrophysics, Gamma-rays
The Equatorial Jet Speed on Tidally Locked Planets. I. Terrestrial Planets. The atmospheric circulation of tidally locked planets is dominated by a superrotating eastward equatorial jet. We develop a predictive theory for the formation of this jet, proposing a mechanism in which the three-dimensional stationary waves induced by the day-night forcing gradient produce an equatorial acceleration. This is balanced in equilibrium by an interaction between the resulting jet and the vertical motion of the atmosphere. The three-dimensional structure of the zonal acceleration is vital to this mechanism. We demonstrate this mechanism in a hierarchy of models. We calculate the three-dimensional stationary waves induced by the forcing on these planets and show the vertical structure of the zonal acceleration produced by these waves, which we use to suggest a mechanism for how the jet forms. General circulation model simulations are used to confirm the equilibrium state predicted by this mechanism, where the acceleration from these waves is balanced by an interaction between the zonal-mean vertical velocity and the jet. We derive a simple model of this using the "Weak Temperature Gradient" approximation, which gives an estimate of the jet speed on a terrestrial tidally locked planet. We conclude that the proposed mechanism is a good description of the formation of an equatorial jet on a terrestrial tidally locked planet and should be useful for interpreting observations and simulations of these planets. The mechanism requires assumptions such as a large equatorial Rossby radius and weak acceleration due to transient waves, and a different mechanism may produce the equatorial jets on gaseous tidally locked planets.

Keywords: Exoplanet atmospheres, Atmospheric circulation
The ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: The Nature of the Faintest Dusty Star-forming Galaxies. We present a characterization of the physical properties of a sample of 35 securely detected, dusty galaxies in the deep ALMA 1.2 mm image obtained as part of the ALMA Spectroscopic Survey in the Hubble Ultra Deep Field (ASPECS) Large Program. This sample is complemented by 26 additional sources identified via an optical/infrared source positional prior. Using their well-characterized spectral energy distributions, we derive median stellar masses and star formation rates (SFR) of $4.8\times {10}^{10}\,{M}_{\odot }$ and 30 M☉ yr-1, respectively, and interquartile ranges of (2.4-11.7) × 1010 M☉ and 20-50 M☉ yr-1. We derive a median spectroscopic redshift of 1.8 with an interquartile range 1.1-2.6, significantly lower than submillimeter galaxies detected in shallower, wide-field surveys. We find that 59% ± 13%, 6% ± 4%, and 34% ± 9% of our sources are within, above, and below±0.4 dex from the SFR-stellar-mass relation or main sequence (MS), respectively. The ASPECS galaxies closely follow the SFR-molecular gas mass relation and other previously established scaling relations, confirming a factor of five increase of the gas-to-stellar-mass ratio from z = 0.5 to 2.5 and a mild evolution of the gas depletion timescales with a typical value of 0.7 Gyr at z = 1-3. ASPECS galaxies located significantly below the MS, a poorly exploited parameter space, have low gas-to-stellar-mass ratios of ∼0.1-0.2 and long depletion timescales &gt;1 Gyr. Galaxies along the MS dominate the cosmic density of molecular gas at all redshifts. Systems above the MS have an increasing contribution to the total gas reservoirs from z &lt; 1 to z = 2.5, while the opposite is found for galaxies below the MS.

Keywords: Submillimeter astronomy, Galaxy quenching, High-redshift galaxies, Galaxy evolution
Astrophysical Background and Dark Matter Implication Based on Latest AMS-02 Data. The cosmic-ray (CR) positrons and antiprotons are often regarded as the collision products of CR nucleons with the interstellar medium. However, the predicted fluxes of CR positrons and antiprotons by the conventional models are not consistent with the experimental data from PAMELA, Fermi-LAT, AMS-02, etc. In this work, we choose the latest AMS-02 data to analyze the astrophysical background of CR positrons and antiprotons. QGSJET-II-04 is chosen as the hadronic interaction model. The GALPROP package is used to solve the propagation equation numerically. The results show that the predicted flux of CR positrons at low energies is consistent with AMS-02 data in the reacceleration and convection-diffusion (DCR) model. In the DCR model and the hadronic interaction model, QGSJET-II-04, the excess of CR antiprotons at low energies is excluded. The dark matter interpretation of the positron excess is analyzed with the total fluxes of CR electrons and positrons from AMS-02. The predicted best-fit mass of dark matter ranges from 400 GeV to 4 TeV. Moreover, in the above models the predicted flux of CR protons is completely consistent with AMS-02 data, which matches the hardening feature above 330 GeV.

Keywords: Galactic cosmic rays, Dark matter
Evolution of CAI-sized Particles during FU Orionis Outbursts. I. Particle Trajectories in Protoplanetary Disks with Beta Cooling. Solar-type young stellar objects undergo periodic, energetic outbursts that appear to be the result of enhanced mass accretion driven by the gravitational instability of their disks. Such FU Orionis outbursts may have profound consequences for the earliest solids in a protoplanetary disk, namely the refractory inclusions containing abundant calcium and aluminum (CAIs). We present models of the orbital evolution of centimeter-radius particles representing large CAIs in marginally gravitationally unstable disks. The hydrodynamical evolution of the disks is calculated with a fully three-dimensional code, including compressional heating and cooling in the beta cooling approximation. The particles are initially distributed uniformly throughout the disk, which extends from 1 to 10 au around a solar-mass protostar, but within ∼100 yr the particles are concentrated by gas drag into regions surrounding the spiral arms and rings formed by the gas disk. The particles settle down toward the disk midplane, only to be lofted repeatedly upward by shock fronts. Large-scale radial transport both outward and inward occurs, with significant numbers of particles reaching the outer disk (∼10 au) and surviving for considerably longer times than would be the case in a quiescent disk with gas pressure monotonically decreasing with distance from the protostar. Individual particles experience wide ranges of disk temperatures during their journeys, ranging from 60 K in the outer disk to nearly 2000 K in spiral features. Future work will consider the implications for CAI rims of the thermochemical processing experienced during FU Orionis outbursts.

Keywords: Hydrodynamical simulations, Gravitational instability, Protoplanetary disks, Stellar accretion disks, Planet formation
Faint Stars in a Faint Galaxy. I. Ultradeep Photometry of the Boötes I Ultrafaint Dwarf Galaxy. We present an analysis of new, extremely deep images of the resolved stellar population of the Boötes I ultrafaint dwarf spheroidal galaxy. These new data were taken with the Hubble Space Telescope, using the Advanced Camera for Surveys (Wide Field Camera) and Wide Field Camera 3 (UVIS), with filters F606W and F814W (essentially V and I), as part of a program to derive the low-mass stellar initial mass function in this galaxy. We compare and contrast two approaches to obtaining the stellar photometry, namely, ePSF and DAOPHOT. We identify likely members of Boötes I based on the location of each star on the color-magnitude diagram, obtained with the DAOPHOT photometry from the ACS/WFC data. The probable members lie close to stellar isochrones that were chosen to encompass the known metallicity distribution derived from spectroscopic data of brighter radial velocity member stars and are consistent with the main-sequence turnoff. The resulting luminosity function of the Boötes I galaxy has a 50% completeness limit of 27.4 in F814W and 28.2 in F606W (Vega magnitude system), which corresponds to a limiting stellar mass of $\lesssim 0.3{{ \mathcal M }}_{\odot }$ .

Keywords: Local Group, Galaxy stellar content, HST photometry, Low mass stars, Dwarf spheroidal galaxies