Sazuna/UAT_keywords huggingface dataset:
Amplitude Modulation of Short-timescale Hot Spot Variability. Variability of Classical T Tauri stars (CTTS) occurs over a vast range of timescales. CTTS in particular are subject to variability caused by accretion shocks, which can occur stochastically, periodically, or quasi-periodically on timescales over a few days. The detectability of young planets within these systems is likely hampered by activity; therefore, it is essential that we understand the origin of young star variability over a range of timescales to help disentangle stellar activity from signatures of planetary origin. We present an analysis of the stochastic small-amplitude photometric variability in the K2 lightcurve of CI Tau occurring on timescales of ≲1 day. We find the amplitude of this variability exhibits the same periodic signatures as detected in the large-amplitude variability, indicating that the physical mechanism modulating these brightness features is the same. The periods detected are also in agreement with the rotation period of the star (∼6.6 days) and the orbital period of the planet (∼9.0 days) known to drive pulsed accretion onto the star.

Keywords: Accretion, Exoplanets, Hot Jupiters, Light curves, Stellar activity, Classical T Tauri stars, Stellar accretion disks, Exoplanet formation
Quark Stars in 4D Einstein-Gauss-Bonnet Gravity with an Interacting Quark Equation of State. The detection of gravitational waves (GWs) from a binary neutron star (BNS) has opened a new window on gravitational wave astronomy. With current sensitivities, detectable signals coming from compact objects like neutron stars turn out to be a crucial ingredient for probing their structure, composition, and evolution. Moreover, astronomical observations on pulsars and their mass-radius relations place important constraints on the dense matter equation of state. In this paper, we consider a homogeneous and unpaired charge-neutral three-flavor interacting quark matter with ${ \mathcal O }({m}_{s}^{4})$ corrections that account for the moderately heavy strange quark instead of the naive MIT bag model. We perform a detailed analysis of strange quark stars in the context of the recently proposed 4D Einstein-Gauss-Bonnet (EGB) theory of gravity. However, this theory does not have standard 4D equations. Thus, we show that the equivalence of the actions in the regularized 4D EGB theory and in the original one is satisfied for a spherically symmetric spacetime. We pay particular attention to the possible existence of neutron stars of mass compatible with $M\sim 2{M}_{\odot }$ . Our findings suggest that the fourth-order correction parameter (a4) of the quantum chromodynamic perturbation and coupling constant α of the GB term play an important role in the mass-radius relation as well as the stability of the quark star. Finally, we compare the results with the well-measured limits of pulsars and their mass and radius extracted from the spectra of several X-ray compact sources.

Keywords: Neutron stars, Compact objects
Understanding Polarized Dust Emission from ρ Ophiuchi A in Light of Grain Alignment and Disruption by Radiative Torques. The alignment of dust grains with the ambient magnetic field produces polarization of starlight as well as thermal dust emission. Using the archival SOFIA/HAWC+ polarimetric data observed toward the ρ Ophiuchus (Oph) A cloud hosted by a B star at 89 and 154 μm, we find that the fractional polarization of thermal dust emission first increases with the grain temperature and then decreases once the grain temperature exceeds ≃25-32 K. The latter trend differs from the prediction of the popular RAdiative Torques (RATs) alignment theory, which implies a monotonic increase of the polarization fraction with the grain temperature. We perform numerical modeling of polarized dust emission for the ρ Oph-A cloud and calculate the degree of dust polarization by simultaneously considering the dust grain alignment and rotational disruption by RATs. Our modeling results could successfully reproduce both the rising and declining trends of the observational data. Moreover, we show that the alignment of only silicate grains or a mixture of silicate-carbon grains within a composite structure can reproduce the observational trends, assuming that all dust grains follow a power-law size distribution. Although there are a number of simplifications and limitations to our modeling, our results suggest grains in the ρ Oph-A cloud have a composite structure, and the grain size distribution has a steeper slope than the standard size distribution for the interstellar medium. Combination of SOFIA/HAWC+ data with JCMT observations 450 and 850 μm would be useful to test the proposed scenario based on grain alignment and disruption by RATs.

Keywords: Interstellar dust, Interstellar radiation field, Interstellar dust extinction, Interstellar medium, Polarimetry
Sensitivity Reach of Gamma-Ray Measurements for Strong Cosmological Magnetic Fields. A primordial magnetic field with strength in the 1-10 pG range can resolve the tension between different measurements of the Hubble constant and provide an explanation for the excess opacity in the 21 cm line at redshift 15 &lt; z &lt; 20 if it is present during the recombination and reionization epochs. This field can also survive in the voids of the large-scale structure in the present day universe. We study the sensitivity reach of the gamma-ray technique for measurement of such a relatively strong cosmological magnetic field using deep exposure(s) of the nearest hard spectrum blazar(s) with CTA telescopes. We show that the gamma-ray measurement method can sense the primordial magnetic field with a strength of up to 10-11 G. Combination of the cosmic microwave background and gamma-ray constraints can thus sense the full range of possible cosmological magnetic fields to confirm or rule out their relevance to the problem of the origin of cosmic magnetic fields, as well as their influence on recombination and reionization epochs.

Keywords: Blazars, Extragalactic magnetic fields
Reactive Rate Constants for the C<SUP>+</SUP> + H<SUB>2</SUB>(v = 0, 1) Reaction: An Accurate State-to-state Quantum Dynamical Study. The accurately calculated thermal rate constants of the C+ + H2(v = 0, 1) reaction are important for estimating the CH+ emission spectra in different astronomical environments. In this study, reactive quantum dynamics of the C+ + H2(v = 0, 1) reaction have been investigated with the time-dependent wave packet method on the high-quality potential energy surface recently developed by Guo et al. The simulated total cross sections are compared in detail with previous experimental measurements and dynamical results. The calculated total rate constants are found to be in good agreement with previous quasi-classical results by Herráez-Aguilar et al., except for the v = 0 reaction at low temperatures. The ro-vibrational state-resolved rate constants show that the CH+ product, obtained from both the v = 0 and v = 1 reactions, is significantly populated in the vibrational ground but rotational excited states. In particular, for the v = 0 reaction, the CH+ product is preferably formed at j' = 4, 5 rotational levels, while the CH+ product for the v = 1 reaction prefers rotational excitation j' = 6-8. This finding varies with previous J-shifting calculations by Zanchet et al., owing to the different potential energy surface and methodology employed in the calculations.

Keywords: Theoretical models, Abundance ratios, Astrochemistry, Molecular physics, Interstellar medium
Electron Densities in the Solar Corona Measured Simultaneously in the Extreme Ultraviolet and Infrared. Accurate measurements of electron density are critical for determination of the plasma properties in the solar corona. We compare the electron densities diagnosed from Fe XIII lines observed by the Extreme-Ultraviolet Imaging Spectrometer (EIS) onboard the Hinode mission with the near-infrared (NIR) measurements provided by the ground-based Coronal Multichannel Polarimeter (CoMP). To do that, the emissivity-ratio method based on all available observed lines of Fe XIII is used for both EIS and CoMP. The EIS diagnostics is further supplemented by the results from Fe XII lines. We find excellent agreement, within 10%, between the electron densities measured from both extreme-ultraviolet and NIR lines. In the five regions selected for detailed analysis, we obtain electron densities of log(Ne [cm-3]) = 8.2-8.6. Where available, the background subtraction has a significant impact on the diagnostics, especially on the NIR lines, where the loop contributes less than a quarter of the intensity measured along the line of sight. For the NIR lines, we find that the line center intensities are not affected by stray light within the instrument, and recommend using these for density diagnostics. The measurements of the Fe XIII NIR lines represent a viable method for density diagnostics using ground-based instrumentation.

Keywords: Solar extreme ultraviolet emission, Solar coronal loops, Infrared astronomy, Solar corona, Solar instruments, Solar electromagnetic emission
Magnetic Fields Observed by Voyager 2 in the Heliosheath. We present observations of the magnetic field ${\boldsymbol{B}}$ in the outermost region of the heliosheath made by Voyager 2 (V2) from 2016 to 2018.6, just before V2 entered the magnetic barrier inside of the heliopause. The average magnetic field strength (B) during this interval was relatively large, 0.135 nT, mainly due to numerous merged interaction regions. Sector structure was observed, and the direction of azimuthal angle λ was primarily close to the Parker spiral magnetic field directions 90° and 270°. Thus, the heliospheric current sheet extended to relatively high southern latitudes poleward of V2 (&gt;30°). On smaller scales, distributions of daily increments in B and the components of ${\boldsymbol{B}}$ from 2016 to 2018.6 were accurately described by q-Gaussian distributions. The average values of the nonextensivity parameter q for one-day increments of the components decreased from q = 1.7 ± 0.01 during 2016 (near solar maximum) to q = 1.3 ± 0.1 during 2017 and 2018, as solar activity declined. The BT direction was close to the average magnetic field direction, and V2 measured primarily compressible fluctuations. These new results are also presented in the context of an overview of the observations of the magnetic field in the heliosheath from the termination shock crossing to the heliopause.

Keywords: Heliosheath, Magnetic fields
Multiwavelength Characterization of the High-mass X-Ray Binary Population of M31. We present our analysis of high-quality high-mass X-ray binary (HMXB) candidates in M31 selected from point-source optical counterpart candidates from the Chandra-PHAT survey catalog. We fit the spectral energy distributions of optical counterpart candidates using the Bayesian Extinction and Stellar Tool. We used the best-fit luminosity, effective temperature, radius, and dust reddening for the companion stars in combination with the local star formation history, dust maps of M31, published X-ray spectral fits from XMM-Newton observations, IR colors, and Chandra X-ray hardness ratios to determine our best sample of HMXB candidates. The age distribution of the HMXB sample appears peaked between 10 and 50 Myr, consistent with findings in other nearby galaxies. Using the age distribution and mean star formation rate (SFR), we find that 80-136 HMXBs were produced per unit of SFR over the last 50 Myr and 89-163 HMXBs were produced per unit of SFR over the last 80 Myr, if we expand the assumed age limit beyond the lifetimes of single massive stars. We also calculate the HMXB production rate (HMXBs/M☉) over time, which ranges from 7 × 10-7 to 4 × 10-6 HMXBs/M☉ over the last 80 Myr, in agreement with both theoretical predictions and measured production rates in other galaxies.

Keywords: Andromeda Galaxy, X-ray binary stars, High mass x-ray binary stars, Binary stars
Dynamics of Sunspot Shock Waves in the Chromosphere and Transition Region. We study the dynamics of shock waves observed in the umbra of a sunspot using the spectroscopic observations from the Interface Region Imaging Spectrograph. The presence of a shock significantly deforms the shape of the spectral lines of Mg II, C II, and Si IV. We found that C II 1335.71 Å and Si IV 1393.75 Å show double-peaked profiles that change to a single peak later on. However, the Mg II h 2803.53 Å line first shows flat-top profiles that change into double peaks followed by the single peak. To study the shock dynamics, we isolate the shock component from the spectra by fitting two Gaussians. We find that the lifetime of the shock is largest in the Mg II h 2803.53 Å line. Moreover, the plasma motion shows both the acceleration and deceleration phases of the shock. Yet, in C II 1335.71 Å and Si IV 1393.75 Å, only the deceleration phase is observed. We observe a strong correlation between the largest blueshift of the shock and deceleration for all three spectral lines. We find a positive (negative) correlation between intensities contributed by the shocks in Mg II and C II (Si IV). This suggests that the shocks are first amplified in C II, followed by a decline in the height range corresponding to Si IV. These results may indicate the dissipation of shocks above the formation height of C II, and the shocks may have important roles in the dynamics of the upper chromosphere and transition region above sunspots.

Keywords: Solar activity, Solar chromosphere, Sunspots, Solar transition region
Magnetoacoustic Waves in a Magnetic Slab Embedded in an Asymmetric Magnetic Environment. III. Applications to the Solar Atmosphere. Analytical and numerical modeling of the behavior of magnetohydrodynamic waves in various magnetic geometries can offer a valuable contribution to the field of solar magnetoseismology. Based on analytical results from our previous studies, here we illustrate a few solar applications of these findings concerning the propagation of magnetoacoustic waves in a magnetic slab embedded in an asymmetric environment. Bearing in mind the simplifying assumptions made, this asymmetric model incorporating external magnetic fields can be used to describe a wide variety of multilayered solar features, some of which are observable and have already been studied in solar structures. Specific potential applications are: prominences, polar plumes and their environment, magnetic bright points, and light bridges, as well as adjacent large-scale layers in the solar atmosphere (e.g., the photosphere—interface region—corona triad, or the chromosphere—transition region—corona group). In these individual cases, the appropriate dispersion relations are derived and solved. The obtained wave propagation solutions may serve (i) not just as impetus to be confirmed by high-resolution observations but (ii) also to be exploited for further diagnostic purposes by solar magnetoseismology of these frequently studied magnetic structures.

Keywords: Solar atmosphere, Magnetohydrodynamics, Solar prominences, The Sun, Sunspots, Solar magnetic bright points
Magnetic Helicity Signature and Its Role in Regulating Magnetic Energy Spectra and Proton Temperatures in the Solar Wind. In a previous paper, we found that perpendicular and parallel proton temperatures are clearly associated with the proton-scale turbulence in the solar wind, and magnetic helicity signature appears to be an important indicator in the association. Based on 15 yr of in situ measurements, the present paper further investigates the magnetic helicity of solar wind turbulence and its role in regulating magnetic energy spectra and proton temperatures. Results show that the presence of the helicity signature is very common in solar wind turbulence at scales $0.3\lesssim k{\rho }_{p}\lesssim 1$ , with k being the wavenumber and ρp the proton gyroradius. The sign of the helicity is mostly positive, indicating the dominance of right-handed polarization of the turbulence. The helicity magnitude usually increases with k and ${\beta }_{\parallel p}$ (the proton parallel beta) when $k{\rho }_{p}$ and ${\beta }_{\parallel p}$ are less than unity. As helicity magnitude increases, the power index of the energy spectrum becomes more negative, and the proton temperatures ${T}_{\perp p}$ and ${T}_{\parallel p}$ rise significantly, where ${T}_{\perp p}$ and ${T}_{\parallel p}$ are the perpendicular and parallel temperatures with respect to the background magnetic field. In particular, the rise of ${T}_{\perp p}$ is faster than ${T}_{\parallel p}$ when ${\beta }_{\parallel p}\lt 1$ is satisfied. The faster rise of ${T}_{\perp p}$ with the helicity magnitude may be interpreted as the result of the preferentially perpendicular heating of solar wind protons by kinetic Alfvén wave turbulence.

Keywords: Space plasmas, Plasma physics, Interplanetary turbulence, Solar coronal heating, Solar wind
Nonequilibrium Temperature Evolution of Ionization Fronts during the Epoch of Reionization. The epoch of reionization (EoR) marks the end of the Cosmic Dawn and the beginning of large-scale structure formation in the universe. The impulsive ionization fronts (I-fronts) heat and ionize the gas within the reionization bubbles in the intergalactic medium (IGM). The temperature during this process is a key yet uncertain ingredient in current models. Typically, reionization simulations assume that all baryonic species are in instantaneous thermal equilibrium with each other during the passage of an I-front. Here we present a new model of the temperature evolution for the ionization front by studying nonequilibrium effects. In particular, we include the energy transfer between major baryon species (e-, H I, H II, He I, and He II) and investigate their impacts on the post-ionization front temperature Tre. For a better step-size control when solving the stiff equations, we implement an implicit method and construct an energy transfer rate matrix. We find that the assumption of equilibration is valid for a nonrelativistic ionization front (speed less than ${10}^{9}\,\mathrm{cm}\,{{\rm{s}}}^{-1}$ ), but deviations from equilibrium occur for faster fronts. The post-front temperature Tre is lower by up to 19.7% (at $3\times {10}^{9}\,\mathrm{cm}$ s-1) or 30.8% (at 1010 cm s-1) relative to the equilibrium case.

Keywords: Cosmology, Reionization, Plasma physics, Intergalactic medium
The Carnegie-Chicago Hubble Program. IX. Calibration of the Tip of the Red Giant Branch Method in the Megamaser Host Galaxy, NGC 4258 (M106). In the nearby galaxy NGC 4258, the well-modeled orbital motion of H2O masers about its supermassive black hole provides the means to measure a precise geometric distance. As a result, NGC 4258 is one of a few "geometric anchors" available to calibrate the true luminosities of stellar distance indicators such as the Tip of the Red Giant Branch (TRGB) or the Cepheid Leavitt law. In this paper, we present a detailed study of the apparent magnitude of the TRGB within NGC 4258, using publicly available HST observations optimally situated in the unreddened stellar halo along the minor axis, spanning distances ranging from 8 to 22 kpc in projected galactocentric radius, or $6^{\prime} $ (13 kpc) to $30^{\prime} $ (66 kpc) in distance along the semimajor axis. We undertake a systematic evaluation of the uncertainties associated with measuring the TRGB in this galaxy, based on an analysis of 54 arcmin2 of HST/ACS imaging. After quantifying these uncertainties, we measure the TRGB in NGC 4258 to be F814W0 = 25.347 ± 0.014 (stat) ± 0.042 (sys) mag. Combined with a recent 1.5% megamaser distance to NGC 4258, we determine the absolute luminosity of the TRGB to be ${M}_{{\rm{F}}814{\rm{W}}}^{{\rm{TRGB}}}=-4.050\pm 0.028$ (stat) ± 0.048 (sys) mag. This new calibration agrees to better than 1% with an independent calibration presented in Freedman et al. that was based on detached eclipsing binaries (DEBs) located in the LMC. * Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs GO-9477 and GO-10399.

Keywords: Galaxy stellar disks, Galaxy distances, Stellar populations, Distance measure, Galaxy stellar halos, Linear regression, Population II stars, Stellar distance
No Stagnation Region before the Heliopause at Voyager 1? Inferences from New Voyager 2 Results. We present anisotropy results for anomalous cosmic-ray protons in the energy range ∼0.5-35 MeV from Cosmic Ray Subsystem (CRS) data collected during calibration roll maneuvers for the magnetometer instrument when Voyager 2 (V2) was in the inner heliosheath. We use a new technique to derive for the first time the radial component of the anisotropy vector from CRS data. We find that the CRS-derived radial solar wind speeds, when converted from the radial components of the anisotropy vectors via the Compton-Getting (C-G) effect, generally agree with those similarly derived speeds from the Low Energy Charged Particle experiment using 28-43 keV data. However, they often differ significantly from the radial solar wind speeds measured directly by the Plasma Science (PLS) instrument. There are both periods when the C-G-derived radial solar wind speeds are significantly higher than those measured by PLS and times when they are significantly lower. The differences are not expected nor explained, but it appears that after a few years in the heliosheath the V2 radial solar wind speeds derived from the C-G method underestimate the true speeds as the spacecraft approaches the heliopause. We discuss the implications of this observation for the stagnation region reported along the Voyager 1 trajectory as it approached the heliopause inferred using the C-G method.

Keywords: Heliosheath, Solar wind, Heliosphere, Cosmic rays
The Broadband Counterpart of the Short GRB 200522A at z = 0.5536: A Luminous Kilonova or a Collimated Outflow with a Reverse Shock?. We present the discovery of the radio afterglow and near-infrared (NIR) counterpart of the Swift short gamma-ray burst (GRB) GRB 200522A, located at a small projected offset of ≍1 kpc from the center of a young, star-forming host galaxy at z = 0.5536. The radio and X-ray luminosities of the afterglow are consistent with those of on-axis cosmological short GRBs. The NIR counterpart, revealed by our Hubble Space Telescope observations at a rest-frame time of ≍2.3 days, has a luminosity of ≍(1.3-1.7) × 1042 erg s-1. This is substantially lower than on-axis short GRB afterglow detections but is a factor of ≍8-17 more luminous than the kilonova of GW170817 and significantly more luminous than any kilonova candidate for which comparable observations exist. The combination of the counterpart's color (i - y = -0.08 ± 0.21; rest frame) and luminosity cannot be explained by standard radioactive heating alone. We present two scenarios to interpret the broadband behavior of GRB 200522A: a synchrotron forward shock with a luminous kilonova (potentially boosted by magnetar energy deposition), or forward and reverse shocks from a ≍14°, relativistic (Γ0 ≳ 10) jet. Models that include a combination of enhanced radioactive heating rates, low-lanthanide mass fractions, or additional sources of heating from late-time central engine activity may provide viable alternate explanations. If a stable magnetar was indeed produced in GRB 200522A, we predict that late-time radio emission will be detectable starting ≍0.3-6 yr after the burst for a deposited energy of ≍1053 erg. Counterparts of similar luminosity to GRB 200522A associated with gravitational wave events will be detectable with current optical searches to ≍250 Mpc.

Keywords: Magnetars, R-process, Gamma-ray bursts