Sazuna/UAT_keywords huggingface dataset:
Cosmic-Ray Transport near the Sun. The strongly diverging magnetic field lines in the very inner heliosphere, through the associated magnetic focusing/mirroring forces, can, potentially, lead to highly anisotropic galactic cosmic-ray distributions close to the Sun. Using a simplified analytical approach, validated by numerical simulations, we study the behavior of the galactic cosmic-ray distribution in this newly explored region of the heliosphere and find that significant anisotropies can be expected inside 0.2 au.

Keywords: Interplanetary turbulence, Solar wind, Heliosphere, Cosmic rays
Numerical Solutions of the External Field Effect on the Radial Acceleration in Disk Galaxies. In modified Newtonian dynamics (MOND)-based theories, the strong equivalence principle is generically broken in an idiosyncratic manner, manifested in the action of an "external field effect" (EFE). The internal dynamics in a self-gravitating system is affected even by a constant external field. In disk galaxies, the EFE can induce warps and modify the rotational speeds. Due to the nonlinearity of MOND, it is difficult to derive analytic expressions of this important effect in a disk. Here we study numerically the EFE in two nonrelativistic Lagrangian theories of MOND: the "Aquadratic-Lagrangian" theory (AQUAL) and "Quasilinear MOND" (QUMOND). For AQUAL, we consider only the axisymmetric field configurations with the external field along the disk axis, or a spherical galaxy with test-particle orbits inclined to the external field. For the more manageable QUMOND, we also calculate the three-dimensional field configurations, with the external field inclined to the disk axis. We investigate in particular to what degree an external field modifies the quasi-flat part of rotation curves. While our QUMOND results agree well with published numerical results in QUMOND, we find that AQUAL predicts weaker EFE than published AQUAL results. However, AQUAL still predicts stronger EFE than QUMOND, which demonstrates current theoretical uncertainties. We also illustrate how the MOND prediction on the rising part of the rotation curve, in the inner parts, depends largely on disk thickness but only weakly on a plausible external field for a fixed galaxy model. Finally, we summarize our results for the outer parts as an improved, approximate analytic expression.

Keywords: Gravitation, Computational methods, Non-standard theories of gravity, Modified Newtonian dynamics
Relativistic Particle Transport and Acceleration in Structured Plasma Turbulence. We discuss the phenomenon of energization of relativistic charged particles in three-dimensional incompressible MHD turbulence and the diffusive properties of the motion of the same particles. We show that the random electric field induced by turbulent plasma motion leads test particles moving in a simulated box to be accelerated in a stochastic way, a second-order Fermi process. A small fraction of these particles happen to be trapped in large-scale structures, most likely formed due to the interaction of islands in the turbulence. Such particles get accelerated exponentially, provided their pitch angle satisfies some conditions. We discuss at length the characterization of the accelerating structure and the physical processes responsible for rapid acceleration. We also comment on the applicability of the results to realistic astrophysical turbulence.

Keywords: Magnetohydrodynamics, Particle astrophysics, Cosmic rays
White Dwarf Photospheric Abundances in Cataclysmic Variables-II. White Dwarfs with and without a Mask. Taking advantage of the now-available Gaia EDR3 parallaxes, we carry out an archival Hubble Space Telescope (HST) far-ultraviolet spectroscopic analysis of 10 cataclysmic variable systems, including five carefully selected eclipsing systems. We obtain accurate white dwarf (WD) masses and temperatures, in excellent agreement with the masses for four of the eclipsing systems. For three systems in our sample, BD Pav, HS 2214, and TT Crt, we report the first robust masses for their WDs. We modeled the absorption lines to derive the WD chemical abundances and rotational velocities for each of the 10 systems. As expected, for five higher-inclination (i ≳ 75°) systems, the model fits are improved with the inclusion of a cold absorbing slab (a curtain masking the WD) with N H ≈ 1020-1022 cm-2. Modeling of the metal lines in the HST spectra reveals that seven of the 10 systems have significant subsolar carbon abundance, and six have subsolar silicon abundance, thereby providing further evidence that CV WDs exhibit subsolar abundances of carbon and silicon. We suggest that strong aluminum absorption lines (and iron absorption features) in the spectra of some CV WDs (such as IR Com) may be due to the presence of a thin iron curtain (N H ≈ 1019 cm-2) rather than to suprasolar aluminum and iron abundances in the WD photosphere. The derived WD (projected) rotational velocities all fall in the range ≈100-400 km s-1, all sub-Keplerian similar to the values obtained in earlier studies.

Keywords: White dwarf stars, Cataclysmic variable stars
On the Accuracy of Underground Muon Intensity Calculations. Cosmic-ray muons detected by deep underground and underwater detectors have served as an information source on the high-energy cosmic-ray spectrum and hadronic interactions in air showers for almost a century. The theoretical interest in underground muons has nearly faded away because space-borne experiments probe the cosmic-ray spectrum more directly, and accelerators provide precise measurements of hadron yields. However, underground muons probe unique hadron interaction energies and phase space, which are still inaccessible to present accelerator experiments. The cosmic-ray nucleon energies reach the hundred-TeV and PeV ranges, which are barely accessible with space-borne experiments. Our new calculation combines two modern computational tools: MCEQ for surface muon fluxes and PROPOSAL for underground transport. We demonstrate excellent agreement with measurements of cosmic-ray muon intensities underground within estimated errors. Beyond that, the precision of historical data turns out to be significantly smaller than our error estimates. This result shows that the sources of high-energy atmospheric lepton flux uncertainties at the surface or underground can be significantly constrained without taking more data or building new detectors. The reduction of uncertainties can be expected to impact data analyses at large-volume neutrino telescopes and be used for the design of future ton-scale direct dark matter detectors.

Keywords: High energy astrophysics, Secondary cosmic rays, Neutrino astronomy, Dark matter, Particle astrophysics, Cosmic rays
The Observed Evolution of the Stellar Mass-Halo Mass Relation for Brightest Central Galaxies. We quantify evolution in the cluster-scale stellar mass-halo mass (SMHM) relation's parameters using 2323 clusters and brightest central galaxies (BCGs) over the redshift range 0.03 ≤ z ≤ 0.60. The precision on the inferred SMHM parameters is improved by including the magnitude gap (m gap) between the BCG and fourth-brightest cluster member (M14) as a third parameter in the SMHM relation. At fixed halo mass, accounting for m gap, through a stretch parameter, reduces the SMHM relation's intrinsic scatter. To explore this redshift range, we use clusters, BCGs, and cluster members identified using the Sloan Digital Sky Survey C4 and redMaPPer cluster catalogs and the Dark Energy Survey redMaPPer catalog. Through this joint analysis, we detect no systematic differences in BCG stellar mass, m gap, and cluster mass (inferred from richness) between the data sets. We utilize the Pareto function to quantify each parameter's evolution. We confirm prior findings of negative evolution in the SMHM relation's slope (3.5σ), and detect negative evolution in the stretch parameter (4.0σ) and positive evolution in the offset parameter (5.8σ). This observed evolution, combined with the absence of BCG growth, when stellar mass is measured within 50 kpc, suggests that this evolution results from changes in the cluster's m gap. For this to occur, late-term growth must be in the intracluster light surrounding the BCG. We also compare the observed results to IllustrisTNG 300-1 cosmological hydrodynamic simulations and find modest qualitative agreement. However, the simulations lack the evolutionary features detected in the real data.

Keywords: Galaxy clusters, Brightest cluster galaxies, Galaxy evolution
Multiepoch Optical Spectroscopy of the Post-AGB Star HD 161796. The evolutionary rate of the pulsating post─asymptotic giant branch (post-AGB) star HD 161796 was suspected to be high. Spectra of HD 161796 acquired during a time span of 18 yr are analyzed with the main goal of determining the evolutionary increase in temperature and comparing it with the latest post-AGB star evolutionary models. Inspection of the spectra reveals splitting and significant temporal variation in strong absorption lines, suggesting the presence of shock waves in the atmosphere of the pulsating star. The Hα profiles point to variable incipient mass loss. Most medium-strength lines have variable blue wings, while the red wings remain stationary, presumably due to variations in the warm outflow from the stellar surface. The modeling of the spectra suggests the average value for the effective temperature to be 7275 K, and for surface gravity, a value of log g = 0.7. Different iron abundances are found for different spectra, probably due to the inability to model the pulsating photosphere with stationary atmospheric models. On average, we arrive at [Fe/H] = −0.06. The observed underabundance in neutron capture and some other elements is inferred to be a consequence of dust─gas separation. It is confirmed that, during pulsation, the stellar surface is hotter when the star is smaller in size. The spectra show a 420 K range in effective temperature—a smaller variation than can be found from pulsation-related changes in color. No significant rate of evolution is seen, contrary to earlier suggestions. The initial mass of the star is evaluated to be ⪅2 M ⊙.

Keywords: Post-asymptotic giant branch stars, Late stellar evolution, Stellar pulsations, UU Herculis stars, Interstellar abundances, Stellar atmospheres
S <SUP>5</SUP>: The Orbital and Chemical Properties of One Dozen Stellar Streams. We report the kinematic, orbital, and chemical properties of 12 stellar streams with no evident progenitors using line-of-sight velocities and metallicities from the Southern Stellar Stream Spectroscopic Survey (S 5), proper motions from Gaia EDR3, and distances derived from distance tracers or the literature. This data set provides the largest homogeneously analyzed set of streams with full 6D kinematics and metallicities. All streams have heliocentric distances between ~10 and 50 kpc. The velocity and metallicity dispersions show that half of the stream progenitors were disrupted dwarf galaxies (DGs), while the other half originated from disrupted globular clusters (GCs), hereafter referred to as DG and GC streams. Based on the mean metallicities of the streams and the mass-metallicity relation, the luminosities of the progenitors of the DG streams range between those of Carina and Ursa Major I (-9.5 ≲ M  V  ≲ -5.5). Four of the six GC streams have mean metallicities of [Fe/H] &lt; -2, more metal poor than typical Milky Way (MW) GCs at similar distances. Interestingly, the 300S and Jet GC streams are the only streams on retrograde orbits in our dozen-stream sample. Finally, we compare the orbital properties of the streams with known DGs and GCs in the MW, finding several possible associations. Some streams appear to have been accreted with the recently discovered Gaia-Enceladus-Sausage system, and others suggest that GCs were formed in and accreted together with the progenitors of DG streams whose stellar masses are similar to those of Draco to Carina (~105-106 M ⊙).

Keywords: Local Group, Globular star clusters, Stellar streams, Stellar kinematics, Dwarf galaxies, Milky Way Galaxy
Significant Dust-obscured Star Formation in Luminous Lyman-break Galaxies at z   7-8. We make use of Atacama Large Millimeter/submillimeter Array continuum observations of 15 luminous Lyman-break galaxies at z ~ 7-8 to probe their dust-obscured star formation. These observations are sensitive enough to probe obscured star formation rates (SFRs) of 20 M ☉ yr-1 (3σ). Six of the targeted galaxies show significant (≥3σ) dust-continuum detections, more than doubling the number of known dust-detected galaxies at z &gt; 6.5. Their IR luminosities range from 2.7 × 1011 L ☉ to 1.1 × 1012 L ☉, equivalent to obscured SFRs of 25 to 101 M ☉ yr-1. We use our results to quantify the correlation of the infrared excess (IRX) on the UV-continuum slope β UV and stellar mass. Our results are most consistent with a Small Magellanic Cloud (SMC) attenuation curve for intrinsic UV-slopes ${\beta }_{\mathrm{UV},\mathrm{intr}}$ of -2.63 and most consistent with an attenuation curve in between SMC and Calzetti for ${\beta }_{\mathrm{UV},\mathrm{intr}}$ slopes of -2.23, assuming a dust temperature T  d  of 50 K. Our fiducial IRX-stellar mass results at z ~ 7-8 are consistent with marginal evolution from z ~ 0. We then show how both results depend on T  d . For our six dust-detected sources, we estimate their dust masses and find that they are consistent with dust production from supernovae if the dust destruction is low (&lt;90%). Finally we determine the contribution of dust-obscured star formation to the SFR density for UV luminous (H&lt;-21.5 mag: ≳1.7 L * UV) z ~ 7-8 galaxies, finding that the total SFR density at z ~ 7 and z ~ 8 from bright galaxies is ${0.20}_{-0.10}^{+0.10}$ dex and ${0.23}_{-0.09}^{+0.06}$ dex higher, respectively; i.e., ~ $\tfrac{1}{3}$ of the star formation in ≳1.7 L * UV galaxies at z ~ 7-8 is obscured by dust.

Keywords: Interstellar dust, Interstellar dust extinction, Galaxy evolution, Lyman-break galaxies, High-redshift galaxies, Galaxies
Temporal Variations of the Three Geomagnetic Field Components at Colaba Observatory around the Carrington Storm in 1859. The Carrington storm in 1859 September has been arguably identified as the greatest geomagnetic storm ever recorded. However, its exact magnitude and chronology remain controversial, while their source data have been derived from the Colaba H magnetometer in India. Here, we have located the Colaba 1859 yearbook, containing hourly measurements and spot measurements. We have reconstructed the Colaba geomagnetic disturbances in the horizontal component (ΔH), the eastward component (ΔY), and the vertical component (ΔZ) around the time of the Carrington storm. On their basis, we have chronologically revised the interplanetary coronal mass ejection transit time as ≤17.1 hr and located the ΔH peak at 06:20-06:25 UT, revealing a magnitude discrepancy between the hourly and spot measurements (-1691 nT versus -1263 nT). Furthermore, we have newly derived the time series of ΔY and ΔZ, which peaked at ΔY ≈ 378 nT (05:50 UT) and 377 nT (06:25 UT), and ΔZ ≈ -173 nT (06:40 UT). We have also computed their hourly averages and removed their solar quiet field variations in each geomagnetic component to derive their hourly disturbance variations (Dist) with latitudinal weighting. Our calculations have resulted in disturbance variations with latitudinal weighting of Dist Y ≈ 328 nT and Dist Z ≈ -36 nT, and three scenarios of Dist H ≈ -918, -979, and -949 nT, which also approximate the minimum Dst. These data may suggest preconditioning of the geomagnetic field after the August storm (ΔH ≤ -570 nT), which made the September storm even more geoeffective.

Keywords: Space weather, Geomagnetic fields, Solar coronal mass ejections, Solar-terrestrial interactions
Standing Sausage Perturbations in Solar Coronal Loops with Diffuse Boundaries: An Initial Value Problem Perspective. Working in pressureless magnetohydrodynamics, we examine the consequences of some peculiar dispersive properties of linear fast sausage modes (FSMs) in one-dimensional cylindrical equilibria with a continuous radial density profile (ρ 0(r)). As recognized recently on solid mathematical grounds, cutoff axial wavenumbers may be absent for FSMs when ρ 0(r) varies sufficiently slowly outside the nominal cylinder. Trapped modes may therefore exist for arbitrary axial wavenumbers and density contrasts, their axial phase speeds in the long-wavelength regime differing little from the external Alfvén speed. If these trapped modes indeed show up in the solutions to the associated initial value problem (IVP), then FSMs have a much better chance to be observed than expected with classical theory and can be invoked to account for a considerably broader range of periodicities than practiced. However, with axial fundamentals in active region loops as an example, we show that this long-wavelength expectation is not seen in our finite-difference solutions to the IVP, the reason for which is then explored by superposing the necessary eigenmodes to construct solutions to the same IVP. At least for the parameters we examine, the eigenfunctions of trapped modes are characterized by a spatial extent well exceeding the observationally reasonable range of the spatial extent of initial perturbations, meaning a negligible fraction of energy that a trapped mode can receive. We conclude that the absence of cutoff wavenumbers for FSMs in the examined equilibrium does not guarantee a distinct temporal behavior.

Keywords: Solar coronal seismology, Magnetohydrodynamics, Solar coronal waves, Solar corona
AWSoM Magnetohydrodynamic Simulation of a Solar Active Region with Realistic Spectral Synthesis. For the first time, we simulate the detailed spectral line emission from a solar active region (AR) with the Alfvén Wave Solar Model (AWSoM). We select an AR appearing near disk center on 2018 July 13 and use the National Solar Observatory's Helioseismic and Magnetic Imager synoptic magnetogram to specify the magnetic field at the model's inner boundary. To resolve small-scale magnetic features, we apply adaptive mesh refinement with a horizontal spatial resolution of 0°.35 (4.5 Mm), four times higher than the background corona. We then apply the SPECTRUM code, using CHIANTI spectral emissivities, to calculate spectral lines forming at temperatures ranging from 0.5 to 3 MK. Comparisons are made between the simulated line intensities and those observed by Hinode/Extreme-ultraviolet Imaging Spectrometer where we find close agreement across a wide range of loop sizes and temperatures (about 20% relative error for both the loop top and footpoints at a temperature of about 1.5 MK). We also simulate and compare Doppler velocities and find that simulated flow patterns are of comparable magnitude to what is observed. Our results demonstrate the broad applicability of the low-frequency AWSoM for explaining the heating of coronal loops.

Keywords: Magnetohydrodynamics, Solar coronal waves, Solar corona, Spectrophotometry, Magnetohydrodynamical simulations
The Habitable Zones of Rapidly Rotating Main Sequence A/F Stars. We investigate how rapid stellar rotation commonly seen in A/F stars can influence planet habitability. Specifically, we model how rapid rotation influences a planet's irradiation and determine the location of the habitable zone for stars in the mass range 1.3 M ⊙ ≤ M ⋆ ≤ 2.2 M ⊙. Rapid stellar rotation can dramatically change a star's luminosity and spectral energy distribution, and therefore can affect the habitability of any surrounding planets. Stars of mass M ⋆ ≳ 1.3 M ⊙ commonly rotate near their breakup speeds, which causes two effects relevant to planet habitability. First, these stars flatten into oblate spheroids with shorter polar radii and elongated equatorial radii. Second, rapid rotation induces a pole-to-equator temperature gradient on the surface of these stars. Using a 1D climate model, we calculate the inner and outer edges of the habitable zone of well-known rapid rotators and average theoretical stars in our stellar mass range. We find that, in general, rapid rotation causes the habitable zone to reside closer in than for a nonrotating equivalent star. We also find that gravity darkening dramatically reduces stellar UV emission, which combats the common assumption that high-mass stars emit too much UV light for habitable worlds. Overall, we determine that rapid stellar rotation has important consequences for the overall habitability of a system and must be accounted for both when modeling exoplanet environments and in observation of planets around high-mass stars.

Keywords: Exoplanets, Planet hosting stars, Stellar rotation, Habitable zone, Habitable planets, Gravity darkening
Coherence of Ion Cyclotron Resonance in Damped Ion Cyclotron Waves in Space Plasmas. Ion cyclotron resonance is one of the fundamental energy-conversion processes through field-particle interaction in collisionless plasmas. However, the key evidence for ion cyclotron resonance (i.e., the coherence between electromagnetic fields and the ion phase-space density) and the resulting damping of ion cyclotron waves (ICWs) has not yet been directly observed. Investigating the high-quality measurements of space plasmas by the Magnetospheric Multiscale (MMS) satellites, we find that both the wave electromagnetic field vectors and the bulk velocity of the disturbed ion velocity distribution rotate around the background magnetic field. Moreover, we find that the absolute gyrophase angle difference between the center of the fluctuations in the ion velocity distribution functions and the wave electric field vectors falls in the range of (0, 90)°, consistent with an ongoing energy conversion from wave fields to particles. By invoking plasma kinetic theory, we demonstrate that the field-particle correlation for the damped ICWs in our theoretical model matches well with our observations. Furthermore, the wave electric field vectors ( $\delta {{\boldsymbol{E}}}_{\mathrm{wave},\perp }^{{\prime} }$ ), ion current density (δ J i,⊥), and energy transfer rate ( $\delta {{\boldsymbol{J}}}_{{\rm{i}},\perp }\cdot \delta {{\boldsymbol{E}}}_{\mathrm{wave},\perp }^{{\prime} }$ ) exhibit quasiperiodic oscillations, and the integrated work done by the electromagnetic field on the ions is positive, indicating that ions are mainly energized by the perpendicular component of the electric field via cyclotron resonance. Therefore, our combined analysis of MMS observations and kinetic theory provides direct, thorough, and comprehensive evidence for ICW damping in space plasmas.

Keywords: Space plasmas, Alfven waves, Plasma physics