Sazuna/UAT_keywords huggingface dataset:
Star-density Profiles of Six Old Star Clusters in the Large Magellanic Cloud. We used resolved star counts from Hubble Space Telescope (HST) images to determine the center of gravity and the projected density profiles of six old globular clusters (GCs) in the Large Magellanic Cloud (LMC), namely NGC 1466, NGC 1841, NGC 1898, NGC 2210, NGC 2257, and Hodge 11. For each system, the LMC field contribution was properly taken into account by making use, when needed, of parallel HST observations. The derived values of the center of gravity may differ by several arcseconds (corresponding to more dal 1 pc at the distance of the LMC) from previous determinations. The cluster density profiles are all well fit by King models, with structural parameters that may differ from the literature ones by even factors of two. Similar to what was observed for Galactic GCs, the ratio between the effective and the core radius has been found to anticorrelate with the cluster dynamical age.

Keywords: Globular star clusters, Magellanic Clouds, HST photometry
Electron Temperatures in the Dayside Ionosphere of Mars Derived from {{{\rm{O}}}_{2}}^{+} Chemistry. From a reduced chemical model of the Martian dayside ionosphere we derive an expression that can be used to estimate the electron temperature as a function of the ambient number densities of CO2, O, {{{{O}}}2}+, {CO}}2}+, O+, and NO+ and the total ion number density. The model is tested in the sunlit ionosphere with Mars Atmosphere and Volatile EvolutioN/Neutral Gas Ion Mass Spectrometer (MAVEN/NGIMS) data from the Deep Dip campaigns DD2 (2015 April) and DD8 (2017 October). Around an altitude of ∼130-140 km the calculated electron temperatures along the DD2 orbits are in many cases compatible with the neutral temperatures derived from the CO2 density profiles and downward integration of the hydrostatic balance equation, indicating efficient cooling of the electron population. For altitudes below 170 km the electron temperature (constructed from median density profiles) are higher for DD8 than for DD2 which we link to atmospheric solar cycle modulation. Median electron temperatures derived for DD2 and DD8 are roughly similar when inspecting similar CO2 number densities and a simple power law is proposed to relate the electron temperature to the CO2 number density. Calculated electron temperatures of approximately 1000 K around an altitude of 180-200 km appear not to conflict with published data from MAVEN Langmuir Probe Wave (LPW) measurements. At greater depths the LPW-derived electron temperatures have been reported as biased high and so a detailed comparison with results from the present work is merely proposed as a dedicated follow-up study.

Keywords: Mars, Plasma physics, Earth ionosphere
A Kinematic Shift of the C IV Broad Absorption Line in Quasar SDSS J120819.29+035559.4. We report the kinematic shift of the C IV broad absorption line (BAL) in quasar SDSS J120819.29+035559.4 (hereafter J1208+0355). This quasar shows two BAL systems, including a blue component of system A at ∼23,500 km s-1 that shows a kinematic shift of 1166 ± 65 km s-1, and a red component of system B at ∼7000 km s-1 that can be decomposed into several narrow absorption lines (NALs). First, we confirm that the most likely cause for the equivalent width variations of the absorption lines (at least for system B) in J1208+0355 is the ionization change scenario as a response to the changes in the ionization continuum according to the following observational factors: (1) coordinated multiple absorption lines strengthening; (2) the continuum flux shows an obvious weakening. Second, we find line-locking phenomena from the blended NALs within system B, indicating that these outflow clouds are driven by a radiative force caused by resonance lines. The above two research aspects convincingly reveal that the BAL outflows of J1208+0355 are affected by the background radiation energy. Therefore, we infer that the kinematic shift shown in system A may be produced by actual line-of-sight acceleration of the outflow clouds, which is driven by radiation pressure from the background light source.

Keywords: Quasar absorption line spectroscopy, Broad-absorption line quasar, Quasars
The Density Gradient Inside Molecular-gas Clumps as a Booster of Their Star Formation Activity. Star-forming regions presenting a density gradient experience a higher star formation rate than if they were of uniform density. We refer to the ratio between the star formation rate of a spherical centrally concentrated gas clump and the star formation rate that this clump would experience if it were of uniform density as the magnification factor ζ. We map ζ as a function of clump mass, radius, initial volume-density profile, and star formation timespan. For clumps with a steep density profile (i.e., a power-law slope ranging from -3 to -4, as observed in some high-density regions of Galactic molecular clouds), we find their star formation rate to be at least an order of magnitude higher than their top-hat equivalent. This implies that such clumps experience faster and more efficient star formation than expected based on their mean freefall time. This also implies that measurements of the star formation efficiency per freefall time of clumps based on their global properties, namely, mass, mean volume density, and star formation rate, present wide fluctuations. These reflect the diversity in the density profile of star-forming clumps, not necessarily variations in the physics of star formation. Steep density profiles inside star-cluster progenitors may be instrumental in the formation of multiple stellar populations, such as those routinely observed in old globular clusters.

Keywords: Star formation, Molecular clouds, Star clusters
The Progenitors of Calcium-strong Transients. A new class of faint, spectroscopically peculiar transients has emerged in the last decade. We term these events “calcium-strong transients” (CaSTs) because of their atypically high calcium-to-oxygen nebular line ratios. Previous studies have struggled to deduce the identity of their progenitors, due to a combination of their extremely extended radial distributions with respect to their host galaxies and their relatively high rate of occurrence. In this work, we find that the CaST radial distribution is consistent with the radial distribution of two populations of stars: old (ages &gt;5 Gyr), low-metallicity (Z/Z ⊙ &lt; 0.3) stars, and globular clusters. While no obvious progenitor scenario arises from considering old, metal-poor stars, the alternative production site of globular clusters leads us to narrow down the list of possible candidates to three binary scenarios: mergers of helium and oxygen/neon white dwarfs; tidal disruptions of helium white dwarfs by neutron stars; and stable accretion from low-mass helium-burning stars onto white dwarfs. While rare in the field, these binary systems can be formed dynamically at much higher rates in globular clusters. Subsequent binary hardening both increases their interaction rate and ejects them from their parent globular clusters prior to mass transfer contact. Their production in, and ejection from, globular clusters may explain their radial distribution and the absence of globular clusters at their explosion site. This model predicts a currently undiscovered high rate of CaSTs in nuclear star clusters. Alternatively, an undetermined progenitor scenario involving old, low-metallicity stars may instead hold the key to understanding CaSTs.

Keywords: White dwarf stars, Binary stars, Supernovae
Exact Analytical Expression for the Synchrotron Radiation Spectrum in the Gaussian Turbulent Magnetic Field. We demonstrate that the exact solution for the spectrum of synchrotron radiation from an isotropic population of monoenergetic electrons in a turbulent magnetic field with a Gaussian distribution of local field strengths can be expressed in the simple analytic form: {≤ft(\tfrac{d\dot{N}}{dω }\right)}t=\tfrac{α }{3}\tfrac{1}{{γ }2}≤ft(1+\tfrac{1}{{x}2/3}\right)\exp ≤ft(-2{x}2/3\right), where x=\tfrac{ω }{{ω }0};{ω }0=\tfrac{4}{3}{γ }2\tfrac{{{eB}}0}{{m}ec}. We use this expression to find the approximate synchrotron spectra for power-law electron distributions with \propto \exp ≤ft(-{≤ft[γ /{γ }0\right]}β \right)-type high-energy cutoff; the resulting synchrotron spectrum has the exponential cutoff factor with a frequency raised to the 2β/(3β + 4) power in the exponent. For the power-law electron distribution without a high-energy cutoff, we find the coefficient a  m  as a function of the power-law index, which results in the exact expression for the synchrotron spectrum when using the monochromatic (i.e., each electron radiates at the frequency {ω }m={a}m{γ }2 \tfrac{{{eB}}0}{{m}ec}) approximation.

Keywords: Non-thermal radiation sources, Magnetic fields, Interstellar synchrotron emission
X-Ray Spectra from Plasmas with High-energy Electrons: κ-distributions and e<SUP>-</SUP>-e<SUP>-</SUP> Bremsstrahlung. Shocks, turbulence, and winds all influence the electron velocity distribution in hot plasmas, exciting lower-energy electrons and generating a high-energy (typically power-law) tail. This effect, typically described as a κ distribution can affect both the line and continuum X-ray spectra emitted by the plasma. Hahn &amp; Savin proposed a “Maxwellian decomposition” to generate the rate coefficients of κ distributions. Using their method and the AtomDB atomic database, we have developed a general model to calculate the emission from a plasma with a κ distribution. We compare our κ results for the charge state distribution and spectra of oxygen with those from KAPPA package with the ion data available within the CHIANTI atomic database. Sufficiently energetic electrons, created either in a κ distribution or merely a very hot Maxwellian plasma, can also emit via electron-electron (e-e) bremsstrahlung, a process not previously included in AtomDB. We have added this process to AtomDB and apply it to calculate the temperature gradients, as well as the total spectra from the post-shock regions of an accreting magnetic cataclysmic variable. We find the contribution of e-e bremsstrahlung to the total spectra exceeds 10% at KT ∼ 100 keV, with the total emissivity in the post-shock accretion stream differing by more than 10% at energies above 60 keV.

Keywords: X-ray astronomy, Atomic physics, White dwarf stars, Laboratory astrophysics, Atomic spectroscopy, Non-thermal radiation sources
On the Gas Content, Star Formation Efficiency, and Environmental Quenching of Massive Galaxies in Protoclusters at z ≈ 2.0-2.5. We present ALMA Band 6 (ν = 233 GHz, λ = 1.3 mm) continuum observations toward 68 “normal” star-forming galaxies within two Coma-like progenitor structures at z = 2.10 and 2.47, from which ISM masses are derived, providing the largest census of molecular gas mass in overdense environments at these redshifts. Our sample comprises galaxies with a stellar mass range of 1 × 109 M ⊙-4 × 1011 M ⊙ with a mean M ⋆ ≈ 6 × 1010 M ⊙. Combining these measurements with multiwavelength observations and spectral energy distribution modeling, we characterize the gas mass fraction and the star formation efficiency, and infer the impact of the environment on galaxies’ evolution. Most of our detected galaxies (≳70%) have star formation efficiencies and gas fractions similar to those found for coeval field galaxies and in agreement with the field scaling relations. However, we do find that the protoclusters contain an increased fraction of massive, gas-poor galaxies, with low gas fractions (f gas ≲ 6%-10%) and red rest-frame ultraviolet/optical colors typical of post-starburst and passive galaxies. The relatively high abundance of passive galaxies suggests an accelerated evolution of massive galaxies in protocluster environments. The large fraction of quenched galaxies in these overdense structures also implies that environmental quenching takes place during the early phases of cluster assembly, even before virialization. From our data, we derive a quenching efficiency of ɛ  q  ≈ 0.45 and an upper limit on the quenching timescale of τ  q  &lt; 1 Gyr.

Keywords: Submillimeter astronomy, Quenched galaxies
The Spin of the Black Hole GRS 1716-249 Determined from the Hard Intermediate State. We present three simultaneous/quasi-simultaneous NuSTAR and Swift data sets of the black hole (BH) GRS 1716-249 in its hard intermediate state. The accretion disk in this state may have reached the innermost stable circular orbit, and the NuSTAR spectra show a broad relativistic iron line and a strong Compton hump. To measure the BH spin, we construct a joint model consisting of a relativistic disk model kerrbb and a reflection model relxill, to fit the continuum and the reflection components, respectively. By applying this model to each data set independently, a consistent result is obtained on the BH spin and the disk inclination. The BH spin is a* ≳ 0.92, and the inclination angle (i) is around 40°-50°, based on the measurements of all data sets. In the third data set, a high BH mass (M BH) is strongly disfavored by the spectral fits. By unfreezing the BH mass, we find a* &gt; 0.92, i={49.9}-1.3+1.0 \circ , and M BH &lt; 8.0 M ⊙, at a 90% confidence level. Considering the lower limit derived from a previous optical constraint, M BH is in a range of 4.9-8.0 M ⊙.

Keywords: Accretion, Black hole physics, X-ray binary stars, Rotating black holes
Long-term Variability and Correlation Study of the Blazar 3C 454.3 in the Radio, NIR, and Optical Wavebands. We performed a long-term optical (B, V, R bands), infrared (J and K bands), and radio band (15, 22, 37 GHz band) study of the flat spectrum radio quasar, 3C 454.3, using data collected over a period of more than 8 yr (MJD 54500-57500). The temporal variability, spectral properties, and interwaveband correlations were studied by dividing the available data into smaller segments with more regular sampling. This helped us constrain the size and the relative locations of the emission regions for different wavebands. Spectral analysis of the source revealed the interplay between the accretion disk and jet emission. The source predominantly showed a redder-when-brighter trend, though we observed a bluer-when-brighter trend at high flux levels, which could be a signature of particle acceleration and radiative cooling. Significant correlations with near-zero lag were seen between various optical and infrared bands, indicating that these emission regions are cospatial. Correlations with a time lag of about 10-100 days are seen between the optical/infrared and radio bands indicating these emissions arise from different regions. We also observe the DCF peak lag change from year to year. We try to explain these differences using a curved jet model where the different emission regions have different viewing angles resulting in a frequency-dependent Doppler factor. This variable Doppler factor model explains the variability timescales and the variation in DCF peak lag between the radio and optical emissions in different segments. Lags of 6-180 days are seen between emissions in various radio bands, indicating a core-shift effect.

Keywords: Observational astronomy, Blazars, Relativistic jets, Galaxy jets, Radio loud quasars, Active galactic nuclei, Photometry
Synthetic Large-scale Galactic Filaments: On Their Formation, Physical Properties, and Resemblance to Observations. Using a population of large-scale filaments extracted from an AREPO simulation of a Milky Way-like galaxy, we seek to understand the extent to which observed large-scale filament properties (with lengths ≳100 pc) can be explained by galactic dynamics alone. From an observer’s perspective in the disk of the galaxy, we identify filaments forming purely due to galactic dynamics, without the effects of feedback or local self-gravity. We find that large-scale galactic filaments are intrinsically rare, and we estimate that at maximum approximately one filament per kpc2 should be identified in projection, when viewed from the direction of our Sun in the Milky Way. In this idealized scenario, we find filaments in both the arm and interarm regions and hypothesize that the former may be due to gas compression in the spiral potential wells, with the latter due to differential rotation. Using the same analysis pipeline applied previously to observations, we analyze the physical properties of large-scale galactic filaments and quantify their sensitivity to projection effects and galactic environment (i.e., whether they lie in the arm or interarm regions). We find that observed “Giant Molecular Filaments” are consistent with being non-self-gravitating structures dominated by galactic dynamics. Straighter, narrower, and denser “Bone-like” filaments, like the paradigmatic Nessie filament, have similar column densities, velocity gradients, and galactic plane heights (z ≈ 0 pc) to those in our simple model, but additional physical effects (such as feedback and self-gravity) must be invoked to explain their lengths and widths.

Keywords: Spiral arms, Galaxy dynamics, Interstellar filaments
New s-process Mechanism in Rapidly Rotating Massive Population II Stars. We report a new mechanism for the s-process in rotating massive metal-poor stars. Our models show that above a critical rotation speed, such stars evolve in a quasi-chemically homogeneous fashion, which gives rise to a prolific s-process. Rotation-induced mixing results in primary production of 13C, which subsequently makes neutrons via {}13{{C}}{(α ,{{n}})}16{{O}} during core He burning. Neutron capture can last up to ∼ {10}13 {{s}} (∼3 × 105 yr) with the peak central neutron density ranging from ∼107 to 108 {cm}}-3. Depending on the rotation speed and the mass loss rate, a strong s-process can occur with production of elements up to Bi for progenitors with initial metallicities of [Z] ≲ -1.5. This result suggests that rapidly rotating massive metal-poor stars are likely the first sites of the main s-process. We find that these stars can potentially explain the early onset of the s-process and some of the carbon-enhanced metal-poor (CEMP-s and CEMP-r/s) stars with strong enrichment attributed to the s-process or a mixture of the r-process and the s-process.

Keywords: Population II stars, Massive stars, Stellar rotation, Stellar nucleosynthesis, CEMP stars, S-process
SN Ia Explosions from Hybrid Carbon-Oxygen-Neon White Dwarf Progenitors that Have Mixed during Cooling. The creation of “hybrid” white dwarfs, made of a C-O core within an O-Ne shell has been proposed, and studies indicate that ignition in the C-rich central region makes these viable progenitors for thermonuclear (type Ia) supernovae. Recent work found that the C-O core is mixed with the surrounding O-Ne as the white dwarf cools prior to accretion, which results in lower central C fractions in the massive progenitor than previously assumed. To further investigate the efficacy of hybrid white dwarfs as progenitors of thermonuclear supernovae, we performed simulations of thermonuclear supernovae from a new series of hybrid progenitors that include the effects of mixing during cooling. The progenitor white dwarf model was constructed with the one-dimensional stellar evolution code Modules for Experiments in Stellar Astrophysics (MESA) and represented a star evolved through the phase of unstable interior mixing followed by accretion until it reached conditions for the ignition of carbon burning. This MESA model was then mapped to a two-dimensional initial condition for explosions simulated with FLASH. For comparison, similar simulations were performed for a traditional C-O progenitor white dwarf. By comparing the yields of the explosions, we find that, as with earlier studies, the lower C abundance in the hybrid progenitor compared to the traditional C-O progenitor leads to a lower average yield of {}56{Ni}. Although the unmixed hybrid white dwarf showed a similar decrement also in total iron-group yield, the mixed case does not and produces a smaller fraction of iron-group elements in the form of {}56{Ni}. We attribute this to the higher central density required for ignition and the location, center or off-center, of deflagration ignition.

Keywords: Hydrodynamical simulations, White dwarf stars, Type Ia supernovae, Explosive nucleosynthesis
Near L-edge Single and Multiple Photoionization of Triply Charged Iron Ions. Relative cross sections for m-fold photoionization (m = 1,…, 5) of Fe3+ by single-photon absorption were measured employing the photon-ion merged-beams setup PIPE at the PETRA III synchrotron light source operated at DESY in Hamburg, Germany. The photon energies used spanned the range of 680-950 eV, covering both the photoexcitation resonances from the 2p and 2s shells, as well as the direct ionization from both shells. Multiconfiguration Dirac-Hartree-Fock (MCDHF) calculations were performed to simulate the total photoexcitation spectra. Good agreement was found with the experimental results. These computations helped to assign several strong resonance features to specific transitions. We also carried out Hartree-Fock calculations with relativistic extensions taking into account both photoexcitation and photoionization. Furthermore, we performed extensive MCDHF calculations of the Auger cascades that result when an electron is removed from the 2p and 2s shells of Fe3+. Our theoretically predicted charge-state fractions are in good agreement with the experimental results, representing a substantial improvement over previous theoretical calculations. The main reason for the disagreement with the previous calculations is their lack of inclusion of slow Auger decays of several configurations that can only proceed when accompanied by de-excitation of two electrons. In such cases, this additional shake-down transition of a (sub)valence electron is required to gain the necessary energy for the release of the Auger electron.

Keywords: De-excitation rates, Photoionization, Atomic physics, Spectral line identification, Atomic data benchmarking
Scattering of Energetic Electrons by Heat-flux-driven Whistlers in Flares. The scattering of electrons by heat-flux-driven whistler waves is explored with a particle-in-cell simulation relevant to the transport of energetic electrons in flares. This simulation is initiated with a large heat flux produced by using a kappa distribution of electrons with positive velocity and a cold return current beam. This system represents energetic electrons escaping from a reconnection-driven energy-release site. This heat-flux system drives large-amplitude oblique whistler waves propagating both along and against the heat flux, as well as electron acoustic waves. While the waves are dominantly driven by the low-energy electrons, including the cold return current beam, the energetic electrons resonate with and are scattered by the whistlers on timescales of the order of a hundred electron cyclotron times. Peak whistler amplitudes of \tilde{B}/{B}0∼ 0.125 and angles of ∼60° with respect to the background magnetic field are observed. Electron perpendicular energy is increased, while the field-aligned electron heat flux is suppressed. The resulting scattering mean-free-paths of energetic electrons are small compared with the typical scale size of energy-release sites in flares, which might lead to the effective confinement of energetic electrons required for the production of very energetic particles.

Keywords: Solar flares, Plasma physics