Sazuna/UAT_keywords huggingface dataset:
Cooling Delays from Iron Sedimentation and Iron Inner Cores in White Dwarfs. Do white dwarfs have inner cores made of iron? Neutron-rich nuclei like 56Fe experience a net gravitational force and sediment toward the core. Using new phase diagrams and molecular dynamics simulations, we show that 56Fe should separate into mesoscopic Fe-rich crystallites due to its large charge relative to the background. At solar abundances, these crystallites rapidly precipitate and form an inner core of order 100 km and 10-3M⊙ that may be detectable with asteroseismology. Associated cooling delays could be up to a Gyr for low-mass white dwarfs but are only ~0.1 Gyr for massive white dwarfs, so while this mechanism may contribute to the Q-branch the heating is insufficient to fully explain it.

Keywords: Stellar interiors, Degenerate matter, White dwarf stars, N-body simulations
Investigating Global Convective Dynamos with Mean-field Models: Full Spectrum of Turbulent Effects Required. The role of turbulent effects for dynamos in the Sun and stars continues to be debated. Mean-field (MF) theory provides a broadly used framework to connect these effects to fundamental magnetohydrodynamics. While inaccessible observationally, turbulent effects can be directly studied using global convective dynamo (GCD) simulations. We measure the turbulent effects in terms of turbulent transport coefficients, based on the MF framework, from an exemplary GCD simulation using the test-field method. These coefficients are then used as an input into an MF model. We find a good agreement between the MF and GCD solutions, which validates our theoretical approach. This agreement requires all turbulent effects to be included, even those which have been regarded as unimportant so far. Our results suggest that simple dynamo models, as are commonly used in the solar and stellar community, relying on very few, precisely fine-tuned turbulent effects, may not be representative of the full dynamics of dynamos in global convective simulations and astronomical objects.

Keywords: Solar cycle, Magnetohydrodynamics, Stellar magnetic fields, Solar dynamo, Stellar activity
Lags in Desorption of Lunar Volatiles. Monte Carlo simulations of gas motion inside a granular medium are presented in order to understand the interaction of lunar gases with regolith and improve models for surface-boundary exospheres, a common type of planetary atmosphere. Results demonstrate that current models underestimate the lifetime of weakly bonded adsorbates (e.g., argon) on the surface by not considering the effect of Knudsen diffusion, and suggest that thermal desorption of adsorbates should be modeled as a second-or-higher-order process with respect to adsorbate coverage. An additional discrepancy between present models and outgassing from a realistic porous boundary is found for surface-adsorbate systems containing a distribution of activation energies (e.g., water). In that case, the mobility of adsorbates between desorption events (i.e., surface diffusion), not considered in global models of the exosphere, controls their surface residence time via transitions between sites of low and high binding energy. Without mobility the equatorial surface retains more water over a lunar day because sites of low binding energy are not repopulated by motion along the grain surface when depleted. The effects of Knudsen and surface diffusion apply to other volatile species and help us partly understand why measurements of lunar exosphere constituents appear to indicate stronger bonding of gas with the lunar surface than measured in some laboratory experiments.

Keywords: Exosphere, Surface processes, The Moon, Lunar surface, Land-atmosphere interactions
Detection of Ionized Calcium in the Atmosphere of the Ultra-hot Jupiter WASP-76b. Recent observations of the ultra-hot Jupiter WASP-76b have revealed a diversity of atmospheric species. Here we present new high-resolution transit spectroscopy of WASP-76b with GRACES at the Gemini North Observatory, serving as a baseline for the Large and Long Program "Exploring the Diversity of Exoplanet Atmospheres at High Spectral Resolution" (Exoplanets with Gemini Spectroscopy, or ExoGemS for short). With a broad spectral range of 400-1050 nm, these observations allow us to search for a suite of atomic species. We recover absorption features due to neutral sodium (Na I), and report a new detection of the ionized calcium (Ca II) triplet at ~850 nm in the atmosphere of WASP-76b, complementing a previous detection of the Ca II H and K lines. The triplet has line depths of 0.295% ± 0.034% at ~849.2 nm, 0.574% ± 0.041% at ~854.2 nm, and 0.454% ± 0.024% at ~866.2 nm, corresponding to effective radii close to (but within) the planet's Roche radius. These measured line depths are significantly larger than those predicted by model LTE and NLTE spectra obtained on the basis of a pressure-temperature profile computed assuming radiative equilibrium. The discrepancy suggests that the layers probed by our observations are either significantly hotter than predicted by radiative equilibrium and/or in a hydrodynamic state. Our results shed light on the exotic atmosphere of this ultra-hot world, and will inform future analyses from the ExoGemS survey.

Keywords: High resolution spectroscopy, Exoplanet atmospheric composition , Transits, Hot Jupiters, Optical astronomy, Exoplanet atmospheric variability, Transmission spectroscopy, Exoplanet atmospheres
Dark Age of Type II Supernova Remnants. Supernova remnants (SNRs) are important objects in terms of their connections with supernova (SN) explosion mechanism(s), progenitor stars, and cosmic-ray acceleration. Nonthermal emission from SNRs is an effective probe of the structure of their surrounding circumstellar media (CSM), which can in turn shed lights on the mechanism and history of the elusive mass loss of massive stars. In this work, we calculate the time evolution of broadband nonthermal emission from SNRs originating from Type II SNe embedded in a CSM environment linked to the mass-loss history of the progenitor. Our results predict that Type II SNRs experience a prolonged period of weak radio and γ-ray emission if they run into a spatially extended bubble of low density and high temperature created by the stellar wind during main sequence. For a typical red supergiant progenitor evolved within an average interstellar medium, this "dark age" corresponds to a range of SNR ages spanning from ~1000 to 5000 yr old. This result suggests that a majority of Type II SNRs are too faint to be detected, which may help explain why the number of known Galactic SNRs is significantly less than what we expect from the SN rate in our Galaxy.

Keywords: Cosmic rays, Submillimeter astronomy, Core-collapse supernovae, Stellar evolution
Generation of High-frequency Whistler Waves in the Earth's Quasi-perpendicular Bow Shock. We use observations from the Magnetospheric Multiscale spacecraft to identify a free energy source for high-frequency whistler waves in the Earth's quasi-perpendicular bow shock. In the considered measurements, whistlers propagate both parallel and antiparallel to the background magnetic field B0 with frequencies around 100 Hz (0.15 fce, where fce is the electron cyclotron frequency) and amplitudes between 0.1 and 1 nT. Their growth can be attributed to localized pitch angle anisotropy in the electron velocity distribution function that cannot be precisely described by macroscopic parameters like heat flux or temperature anisotropy. However, the presence of heat flux along -B0 does create preferential conditions for the high-frequency whistler waves that propagate in this direction. These waves are directed partially toward the shock, meaning they can scatter electrons that are streaming from the shock. This prolongs the time the electrons spend in the shock transition region and thereby promotes electron energization.

Keywords: Shocks
Influence of Heliolatitudinal Anisotropy of Solar FUV/EUV Emissions on Lyα Helioglow: SOHO/SWAN Observations and WawHelioGlow Modeling. Observations of the Sun's surface suggest a nonuniform radiated flux as related to the presence of bright active regions and darker coronal holes. The variations of the FUV/EUV source radiation can be expected to affect the Lyα backscatter glow measured by spaceborne instruments. In particular, inferring the heliolatitudinal structure of the solar wind from helioglow variations in the sky can be quite challenging if the heliolatitudinal structure of the solar FUV/EUV radiation is not properly included in the modeling of the heliospheric glow. We present results of analysis of the heliolatitudinal structure of the solar Lyα radiation as inferred from comparison of SOHO/SWAN satellite observations of the helioglow intensity with modeling results obtained from the recently developed WawHelioGlow model. We find that in addition to time-dependent heliolatitudinal anisotropy of the solar wind, time-dependent heliolatitudinal variations of the intensity of the solar Lyα and photoionizing emissions also must be taken into account to reproduce the observed helioglow modulation in the sky. We present a particular latitudinal and temporal dependence of the solar Lyα flux obtained as a result of our analysis. We also analyze differences between polar-equatorial anisotropies close to the solar surface and seen by an observer located far from the Sun. We discuss the implications of these findings for the interpretation of heliospheric-glow observations.

Keywords: Diffuse radiation, Solar ultraviolet emission, Heliosphere
The Stellar β-decay Rate of <SUP>134</SUP>Cs and Its Impact on the Barium Nucleosynthesis in the s-process. We have calculated the stellar β-decay rate of the important s-process branching point 134Cs based on the state-of-the-art shell model calculations. At typical s-process temperatures (T ~ 0.2-0.3 GK), our new rate is one order of magnitude lower than the widely used rate from Takahashi and Yokoi (hereafter TY87). The impact on the nucleosynthesis in AGB stars is investigated with various masses and metallicities. Our new decay rate leads to an overall decrease in the 134Ba/136Ba ratio, and well explains the measured ratio in meteorites without introducing the i-process. We also derive the elapsed time from the last AGB nucleosynthetic event that polluted the early solar system to be &gt;28 Myr based on the 135Cs/133Cs ratio, which is consistent with the elapsed times derived from 107Pd and 182Hf. The s-process abundance sum of 135Ba and 135Cs is found to increase, resulting in a smaller r-process contribution of 135Ba in the solar system.

Keywords: Asymptotic giant branch, Nucleosynthesis, Nuclear reaction cross sections
Radiation GRMHD Simulations of the Hard State of Black Hole X-Ray Binaries and the Collapse of a Hot Accretion Flow. We present global radiation GRMHD simulations of strongly magnetized accretion onto a spinning, stellar mass black hole at sub-Eddington rates. Using a frequency-dependent Monte Carlo procedure for Compton scattering, we self-consistently evolve a two-temperature description of the ion-electron fluid and its radiation field. For an Eddington ratio L/LEdd ≳ 10-3, the emergent spectrum forms an apparent power-law shape from thermal Comptonization up to a cutoff at ≃100 keV, characteristic of that seen in the hard spectral states of black hole X-ray binary systems. At these luminosities, the radiative efficiency is high (≍24%) and results in a denser midplane region where magnetic fields are dynamically important. For L/LEdd ~ 10-2, our hot accretion flow appears to undergo thermal runaway and collapse. Our simulations demonstrate that hot accretion flows can be radiatively efficient and provide an estimate of their maximum luminosity.

Keywords: Accretion, Black hole physics, Magnetohydrodynamics, X-ray binary stars, Radiative transfer
Formation of a Solar Filament by Magnetic Reconnection and Coronal Condensation. In solar filament formation mechanisms, magnetic reconnection between two sets of sheared arcades forms helical structures of the filament with numerous magnetic dips, and cooling and condensation of plasma trapped inside the helical structures supply mass to the filament. Although each of these processes, namely, magnetic reconnection and coronal condensation have been separately reported, observations that show the whole process of filament formation are rare. In this Letter, we present the formation of a sigmoid via reconnection between two sets of coronal loops, and the subsequent formation of a filament through cooling and condensation of plasma inside the newly formed sigmoid. On 2014 August 27, a set of loops in the active region 12151 reconnected with another set of loops that are located to the east. A longer twisted sigmoidal structure and a set of shorter lower-lying loops then formed. The observations coincide well with the tether-cutting model. The newly formed sigmoid remains stable and does not erupt as a coronal mass ejection. From the eastern endpoint, signatures of injection of material into the sigmoid (as brightenings) are detected, which closely outline the features of increasing emission measure at these locations. This may indicate the chromospheric evaporation caused by reconnection, supplying heated plasma into the sigmoid. In the sigmoid, thermal instability occurs, and rapid cooling and condensation of plasma take place, forming a filament. The condensations then flow bidirectionally to the filament endpoints. Our results provide a clear observational evidence of the filament formation via magnetic reconnection and coronal condensation.

Keywords: Solar ultraviolet emission, Solar magnetic reconnection, Plasma physics, Solar filaments, Solar magnetic fields
Chronicling the Host Galaxy Properties of the Remarkable Repeating FRB 20201124A. We present the Australian Square Kilometre Array Pathfinder localization and follow-up observations of the host galaxy of the repeating fast radio burst (FRB) source, FRB 20201124A, the fifth such extragalactic repeating FRB with an identified host. From spectroscopic observations using the 6.5 m MMT Observatory, we derive a redshift z = 0.0979 ± 0.0001, a star formation rate inferred from Hα emission SFR(Hα) ≈ 2.1 M⊙ yr-1, and a gas-phase metallicity of 12+log(O/H) ≈ 9.0. By jointly modeling the 12 filter optical-mid-infrared (MIR) photometry and spectroscopy of the host, we infer a median stellar mass of ~2 × 1010 M⊙, internal dust extinction AV ≈ 1-1.5 mag, and a mass-weighted stellar population age of ~5-6 Gyr. Connecting these data to the radio and X-ray observations, we cannot reconcile the broadband behavior with strong active galactic nucleus activity and instead attribute the dominant source of persistent radio emission to star formation, likely originating from the circumnuclear region of the host. The modeling also indicates a hot dust component contributing to the MIR luminosity at a level of ~10%-30%. We model the host galaxy's star formation and mass assembly histories, finding that the host assembled &gt;90% of its mass by 1 Gyr ago and exhibited a fairly constant SFR for most of its existence, with no clear evidence of past starburst activity.

Keywords: Neutron stars, Stellar populations, Radio bursts, Star formation, Radio transient sources
A Local Universe Host for the Repeating Fast Radio Burst FRB 20181030A. We report on the host association of FRB 20181030A, a repeating fast radio burst (FRB) with a low dispersion measure (103.5 pc cm-3) discovered by the CHIME/FRB Collaboration et al. Using baseband voltage data saved for its repeat bursts, we localize the FRB to a sky area of 5.3 arcmin2 (90% confidence). Within the FRB localization region, we identify NGC 3252 as the most promising host with an estimated chance-coincidence probability &lt;2.5 × 10-3. Moreover, we do not find any other galaxy with Mr &lt; -15 AB mag within the localization region to the maximum estimated FRB redshift of 0.05. This rules out a dwarf host 5 times less luminous than any FRB host discovered to date. NGC 3252 is a star-forming spiral galaxy and at a distance of ≈20 Mpc, it is one of the closest FRB hosts discovered thus far. From our archival radio data search, we estimate a 3σ upper limit on the luminosity of a persistent compact radio source (source size &lt; 0.3 kpc at 20 Mpc) at 3 GHz to be 2 × 1026 erg s-1 Hz-1, at least 1500 times smaller than that of the FRB 20121102A persistent radio source. We also argue that a population of young millisecond magnetars alone cannot explain the observed volumetric rate of repeating FRBs. Finally, FRB 20181030A is a promising source for constraining FRB emission models due to its proximity and we strongly encourage its multi-wavelength follow-up.

Keywords: Radio bursts, Radio transient sources
A Rotating Azimuthally Distributed Auroral Current System on Saturn Revealed by the Cassini Spacecraft. Stunning aurorae are mainly produced when accelerated electrons travel along magnetic field lines to collide with the atmosphere. The motion of electrons often corresponds to the evolution of a magnetic field-aligned current system. In the terrestrial magnetosphere, the current system is formed at the night-side sector, and thus produces an auroral bulge at night. Due to the different energy sources between Saturn and the Earth, it is expected that their auroral current systems are fundamentally different, although the specific auroral driver at Saturn is poorly understood. Using simultaneous measurements of the aurora, particles, magnetic fields, and energetic neutral atoms, we reveal that a chain of paired currents, each of which includes a downward and an upward current branch, is formed in Saturn's magnetosphere, which generates separated auroral patches. These findings inform similar auroral current structures between the Earth and Saturn, while the difference is that Saturn's unique mass and energy sources lead to a rotational characteristic.

Keywords: Planetary magnetospheres, Saturn, Aurorae
ZTFJ0038+2030: A Long-period Eclipsing White Dwarf and a Substellar Companion. In a search for eclipsing white dwarfs using the Zwicky Transient Facility lightcurves, we identified a deep eclipsing white dwarf with an orbital period of 10.4 hr and an undetected substellar companion. We obtained high-speed photometry and radial velocity measurements to characterize the system. The white dwarf has a mass of 0.50 ± 0.02 M⊙ and a temperature of 10,900 ± 200 K. The companion has a mass of 0.059 ± 0.004 M⊙ and is a brown dwarf. It has a radius of 0.0783 ± 0.0013 R⊙, and is one of the physically smallest transiting brown dwarfs known and likely old, ≳8 Gyr. The ZTF discovery efficiency of substellar objects transiting white dwarfs is limited by the number of epochs and as ZTF continues to collect data we expect to find more of these systems.

Keywords: Eclipsing binary stars, White dwarf stars, Brown dwarfs, Extrasolar gaseous giant planets
von Karman Correlation Similarity of the Turbulent Interplanetary Magnetic Field. A major development underlying much of hydrodynamic turbulence theory is the similarity decay hypothesis due to von Karman and Howarth here extended empirically to magnetic field fluctuations in the solar wind. In similarity decay the second-order correlation experiences a continuous transformation based on a universal functional form and a rescaling of energy and characteristic length. Solar wind turbulence follows many principles adapted from classical fluid turbulence, but previously this similarity property has not been examined explicitly. Here we analyze an ensemble of magnetic correlation functions computed from Advanced Composition Explorer data at 1 au, and demonstrate explicitly that the two-point correlation functions undergo a collapse to a similarity form of the type anticipated from von Karman's hypothesis. This provides for the first time a firm empirical basis for employing the similarity decay hypothesis to the magnetic field, one of the primitive variables of magnetohydrodynamics, and one frequently more accessible from spacecraft instruments. This approach is of substantial utility in space turbulence data analysis, and for adopting von Karman-type heating rates in global and subgrid-scale dynamical modeling.

Keywords: Magnetohydrodynamics, Interplanetary turbulence, Solar wind, Plasma astrophysics, Interplanetary physics
Using Magnetic Flux Conservation to Determine Heliosheath Speeds. The heliosheath (HSH) radial speeds at Voyager 2 (V2) derived from the plasma instrument (PLS) and from particle instruments using the Compton-Getting (CG) effect are different. At V2 the CG speeds are more variable than the plasma speeds and decrease about 2 yr before the heliopause. We use magnetic flux conservation to differentiate between these two speed profiles at V2, comparing the magnetic flux observed at 1 au and in the HSH. For V2 the PLS speed profile is significantly more consistent with magnetic flux conservation than the CG speeds. For Voyager 1 (V1), we present new VR derivations from the Cosmic Ray Subsystem (CRS) using the CG method that agree reasonably well with those previously obtained from the low energy charged particle (LECP) instrument. If we use the V2 PLS speed profile to calculate the magnetic flux at V1, we again find much better agreement than if we use the V1 CG speeds. These results suggest that the radial speeds derived from particle anisotropy observations in the HSH are not reliable.

Keywords: Heliosheath
Decay of Solar Pores Driven by Small-scale Magnetic Reconnection Episodes. We present the relationships between the disappearances of two small pores, magnetic cancellations, and magnetic reconnection episodes in the NOAA AR 12778 on 2020 October 26 with high-resolution observations of the New Vacuum Solar Telescope and the Solar Dynamics Observatory. Two emerging positive polarities (P1 and P2) approach a negative polarity (N1) with velocities of 0.26 and 0.42 km s-1, respectively. Then, two small-scale magnetic reconnection episodes occur between a series of magnetic loops that are rooted in these polarities. The reconnection inflow velocities are around 4.0 km s-1 which is faster than the movements of P1 and P2. Compared with the first magnetic reconnection episode, more magnetic free energy is released in the second reconnection episode due to the greater magnetic strength of P2. Subsequently, magnetic cancellation occurs first between P1 and N1, and then between P2 and N1. At the same time, the pores S1 (N1) and S2 (P2) decay and disappear. The area decay rate of the small pore S2 is estimated to be 7.3 Mm2 hr-1, which is larger than previously reported cases. And the flux decay rate of S2 is 5.1 × 1019 Mx hr-1, similar to the results obtained in the larger sunspots. We conclude that the magnetic reconnection episodes may be caused by both the movement of the magnetic polarities and the plasma dynamics themselves. The decay and disappearance of the small pores and the polarities are driven by magnetic reconnection episodes and then flux submergence. We suggest that a magnetic reconnection episode is a more efficient mechanism for the disappearance of solar pores.

Keywords: Solar activity, Solar magnetic fields, Sunspots, Solar magnetic reconnection