adsabs/SciX_UAT_keywords huggingface dataset:
Modeling of the Polytropic Index and Temperature Anisotropy in the Solar Wind

The polytropic index is a fundamental physical parameter related to the thermodynamic processes present in space and astrophysical plasmas. This paper investigates the theoretical relationship between the polytropic index and the temperature anisotropy for flow parameters relevant to space plasmas. The derivation is based on the Chew–Goldberger–Low double-adiabatic equations of state and the finite Larmor radius correction. On the basis of this, we present the polytropic index relation, taking into account the temperature anisotropy, flow speed, and magnetic field of the plasma. This relation was further analyzed for the limit of the quasi-parallel and quasi-transversal cases. The quasi-transversal limit gives a polytropic index as a function of the anisotropic temperature γ = 1 + 2[2T ⊥ ‑ T ∥]/[2T ⊥ + T ∥]. Using this result, we analyze the polytropic index for the bulk proton parameters derived from Ulysses spacecraft data spanning the interval from 1992 January 1 to 2009 June 30, and we find an average polytropic index of γ ∼ 1.43. This value is close to that of recently published results. However, unlike previous statistical studies, this research computes the polytropic index without relying on power-law fitting, and its variation is now associated with the anisotropic temperature.

Keywords: polytropes; heliosphere; space plasmas; theoretical techniques; solar wind; solar energetic particles
An X-Ray Proper-motion Study of the Large Magellanic Cloud Supernova Remnant 0509-67.5

We present a third epoch of Chandra observations of the Type Ia Large Magellanic Cloud Supernova remnant 0509-67.5. With these new observations from 2020, the baseline for proper-motion measurements of the expansion has grown to 20 yr (from the earliest Chandra observations in 2000). We report here the results of these new expansion measurements. The lack of nearby bright point sources renders absolute image alignment difficult. However, we are able to measure the average expansion of the diameter of the remnant along several projection directions. We find that the remnant is expanding with an average velocity of 6120 (4900-7360) km s-1. This high shock velocity is consistent with previous works, and also consistent with the inference that 0509-67.5 is expanding into a very low density surrounding medium. At the distance of the LMC, this velocity corresponds to an undecelerated age of 600 yr, with the real age somewhat smaller.

Keywords: supernova remnants; interstellar medium
Testing Magnetospheric Accretion as an Hα Emission Mechanism of Embedded Giant Planets: The Case Study for the Disk Exhibiting Meridional Flow Around HD 163296

Recent high-sensitivity observations reveal that accreting giant planets embedded in their parental circumstellar disks can emit Hα at their final formation stages. While the origin of this emission is not yet determined, magnetospheric accretion is currently the most plausible hypothesis. In order to test this hypothesis further, we develop a simplified but physics-based model and apply it to our observations taken toward HD 163296 with Subaru/SCExAO+VAMPIRES. We specify under which conditions embedded giant planets can undergo magnetospheric accretion and emit hydrogen lines. We find that when the stellar accretion rates are high, magnetospheric accretion becomes energetic enough to self-regulate the resulting emission. On the other hand, when massive planets are embedded in disks with low accretion rates, earlier formation histories determine whether magnetospheric accretion occurs. We explore two different origins for the hydrogen emission lines (magnetospheric accretion flow heated by accretion-related processes versus planetary surfaces via accretion shock). The corresponding relationships between the accretion and line luminosities dictate that the emission from accretion flow achieves higher line flux than that from accretion shock, and the flux decreases with increasing wavelengths (i.e., from Hα to Paβ and up to Brγ). Our observations do not detect any point-like source emitting Hα, and they are used to derive the 5σ detection limit. The observations are therefore not sensitive enough, and a reliable examination of our model becomes possible when the observational sensitivity is improved by a factor of 10 or more. Multi-band observations increase the possibility of efficiently detecting embedded giant planets and carefully determining the origin of the hydrogen emission lines.

Keywords: planet formation; extrasolar gaseous giant planets; protoplanetary disks; planetary magnetospheres; h alpha photometry
The Binary and the Disk: The Beauty is Found within NGC3132 with JWST

The planetary nebula (PN) NGC 3132 is a striking example of the dramatic but poorly understood mass-loss phenomena that (1-8) M ⊙ stars undergo during their death throes as they evolve into white dwarfs (WDs). From an analysis of JWST multiwavelength (0.9-18 μm) imaging of NGC 3132, we report the discovery of an extended dust cloud around the WD central star (CS) of NGC 3132, seen most prominently in the 18 μm image, with a surface-brightness-limited radial extent of ≳2″. We show that the A2V star located 1.″7 to CS's northeast (and 0.75 kpc from Earth) is gravitationally bound to the latter, as evidenced by the detection of relative orbital angular motion of 0.°24 ± 0.°045 between these stars over ~20 yr. Using aperture photometry of the CS extracted from the JWST images, together with published optical photometry and an archival UV spectrum, we have constructed the spectral energy distribution (SED) of the CS and its extended emission over the UV to mid-IR (0.091-18 μm) range. We find that fitting the SED of the CS and the radial intensity distributions at 7.7, 12.8, and 18 μm with thermal emission from dust requires a cloud that extends to a radius of ≳1785 au, with a dust mass of ~1.3 × 10-2 M ⊕ and grains that are 70% silicate and 30% amorphous carbon. We propose plausible origins of the dust cloud and an evolutionary scenario in which a system of three stars-the CS, a close low-mass companion, and a more distant A2V star-forms a stable hierarchical triple system on the main sequence but becomes dynamically unstable later, resulting in the spectacular mass ejections that form the current, multipolar PN.

Keywords: circumstellar matter; planetary nebulae nuclei; stellar mass loss; white dwarf stars; circumstellar dust; planetary nebulae; james webb space telescope; hubble space telescope; gaia; ultraviolet spectroscopy; close binary stars; orbit determination
A Maximum Likelihood Calibration of the Tip of the Red Giant Branch Luminosity from High Latitude Field Giants Using Gaia Early Data Release 3 Parallaxes

The calibration of the tip of the red giant branch (TRGB) in the I band has a direct role in determinations of the Hubble constant, a subject of recent interest due to the discrepancy between direct and indirect estimates of its value. We present a maximum likelihood method designed to obtain an independent calibration of the brightness of TRGB using Gaia parallaxes from the Early Data Release 3 (EDR3) of Milky Way field giants at high Galactic latitude. We adopt simple parameterizations for the Milky Way stellar luminosity function and density law and optimize the likelihood of the observed sample as a function of those parameters. Using parameters to partially constrain the luminosity function from other galaxies similar to the Milky Way for which high-quality TRGB data are available, we find values of the TRGB magnitude of ${M}_{I}^{\mathrm{TRGB}}=-3.91\pm 0.05$ (stat) ± 0.09 (sys) mag, where the systematic uncertainty covers the range of shape parameters found in our Milky Way sample and in reference galaxies. While APASS Data Release 9 all-sky photometry is insufficient to provide a reliable constraint on the shape of the Milky Way luminosity function, we estimate that the photometry from Gaia Data Release 3 (mid-2022) will allow better constraints on the shape, and lower statistical uncertainties on the tip by a factor of 3. With the expected releases of improved parallax measurements from Gaia, the method of calibrating the TRGB luminosity from field giants is expected to reach ~0.01 mag uncertainty, which is an important step toward a precise TRGB-based determination of the Hubble constant.

Keywords: milky way galaxy; calibration; red giant tip; distance indicators; hubble constant; parallax; maximum likelihood estimation; absolute magnitude; field stars
The Universe is Brighter in the Direction of Our Motion: Galaxy Counts and Fluxes are Consistent with the CMB Dipole

An observer moving with respect to the cosmic rest frame should observe a concentration and brightening of galaxies in the direction of motion and a spreading and dimming in the opposite direction. The velocity inferred from this dipole should match that of the cosmic microwave background (CMB) temperature dipole if galaxies are on average at rest with respect to the CMB rest frame. However, recent studies have claimed a many-fold enhancement of galaxy counts and flux in the direction of the solar motion compared to the CMB expectation, calling into question the standard cosmology. Here we show that the sky distribution and brightness of extragalactic radio sources are consistent with the CMB dipole in direction and velocity. We use the first epoch of the Very Large Array Sky Survey combined with the Rapid Australian Square Kilometer Array Pathfinder Continuum Survey to estimate the dipole via several different methods, and all show similar results. Typical fits find a ${331}_{-107}^{+161}$ km s-1 velocity dipole with apex $({\ell },b)=({271}_{-58}^{+55},{56}_{-35}^{+13})$ in Galactic coordinates from source counts and ${399}_{-199}^{+264}$ km s-1 toward $({\ell },b)=({301}_{-30}^{+30},{43}_{-17}^{+19})$ from radio fluxes. These are consistent with the CMB-solar velocity, 370 km s-1 toward (ℓ, b) = (264, 48), and show that galaxies are on average at rest with respect to the rest frame of the early universe, as predicted by the canonical cosmology.

Keywords: cosmic anisotropy; solar motion; extragalactic radio sources; radio source catalogs; radio source counts; cosmological models; observational cosmology; relativistic cosmology; special relativity; relativistic aberration
Ground Testing of Digital Terrain Models to Prepare for OSIRIS-REx Autonomous Vision Navigation Using Natural Feature Tracking

The OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer) spacecraft collected a sample from the asteroid Bennu in 2020. This achievement leveraged an autonomous optical navigation approach called Natural Feature Tracking (NFT). NFT provided spacecraft state updates by correlating asteroid surface features rendered from previously acquired terrain data with images taken by the onboard navigation camera. The success of NFT was the culmination of years of preparation and collaboration to ensure that feature data would meet navigation requirements. This paper presents the findings from ground testing performed prior to the spacecraft's arrival at Bennu, in which synthetic data were used to develop and validate the technical approach for building NFT features. Correlation sensitivity testing using synthetic models of Bennu enabled the team to characterize the terrain properties that worked well for feature correlation, the challenges posed by smoother terrain, and the impact of imaging conditions on correlation performance. The team found that models constructed from image data by means of stereophotoclinometry (SPC) worked better than those constructed from laser altimetry data, except when test image pixel sizes were more than a factor of 2 smaller than those of the images used for SPC, and when topography was underrepresented and resulted in incorrect shadows in rendered features. Degradation of laser altimetry data related to noise and spatial sampling also led to poor correlation performance. Albedo variation was found to be a key contributor to correlation performance; topographic data alone were insufficient for NFT.

Keywords: asteroid surfaces; asteroids
Hα Time Delays of Active Galactic Nuclei from the Zwicky Transient Facility Broadband Photometry

In our previous work on broadband photometric reverberation mapping (PRM), we proposed the interpolated cross-correlation function (ICCF)-Cut process to obtain the time lags of the Hα emission line from two broadband lightcurves via subtracting the continuum emission from the line band. Extending the work, we enlarge our sample to the Zwicky Transient Facility (ZTF) database. We adopt two criteria to select 123 type 1 active galactic nuclei (AGNs) with sufficient variability and smooth light curves from 3537 AGNs at z < 0.09 with more than 100 epoch observations in the g and r bands from the ZTF database. We calculate the Hα time lags for 23 of them that have previous spectroscopic reverberation mapping (SRM) results using the ICCF-Cut, Just Another Vehicle for Estimating Lags In Nuclei (JAVELIN), and χ 2 methods. Our obtained Hα time lags are slightly larger than the Hβ time lags, which is consistent with the previous SRM results and the theoretical model of the AGN broad-line region. The comparisons between the SRM and PRM lag distributions and between the subtracted emission line light curves indicate that after selecting AGNs with the two criteria, combining the ICCF-Cut, JAVELIN, and χ 2 methods provides an efficient way to get the reliable Hα lags from the broadband PRM. Such techniques can be used to estimate the black hole masses of a large sample of AGNs in large multiepoch photometric sky surveys such as the Legacy Survey of Space and Time and the survey from the Wide Field Survey Telescope in the near future.

Keywords: active galactic nuclei; reverberation mapping; supermassive black holes
To E or Not to E : Numerical Nuances of Global Coronal Models

In recent years, global coronal models have experienced an ongoing increase in popularity as tools for forecasting solar weather. Within the domain of up to 21.5 R ⊙, magnetohydrodynamics (MHD) is used to resolve the coronal structure using magnetograms as inputs at the solar surface. Ideally, these computations would be repeated with every update of the solar magnetogram so that they could be used in the ESA Modeling and Data Analysis Working Group magnetic connectivity tool (http://connect-tool.irap.omp.eu/). Thus, it is crucial that these results are both accurate and efficient. While much work has been published showing the results of these models in comparison with observations, not much of it discusses the intricate numerical adjustments required to achieve these results. These range from the details of boundary condition formulations to adjustments as large as enforcing parallelism between the magnetic field and velocity. By omitting the electric field in ideal MHD, the description of the physics can be insufficient and may lead to excessive diffusion and incorrect profiles. We formulate inner boundary conditions that, along with other techniques, reduce artificial electric field generation. Moreover, we investigate how different outer boundary condition formulations and grid design affect the results and convergence, with special focus on the density and radial component of the B -field. The significant improvement in accuracy of real magnetic map-driven simulations is illustrated for an example of the 2008 eclipse.

Keywords: magnetohydrodynamical simulations; active solar corona; heliosphere; space weather
Analysis of Solar-like X-class Flare on Wolf 359 Observed Simultaneously with TESS and XMM-Newton

We present an analysis of a flare on the Wolf 359 star based on simultaneous observations of Transiting Exoplanet Survey Satellite and XMM-Newton. A stellar flare with energy comparable to an X-class solar flare is analyzed on this star for the first time. The main goal of the study was to determine whether the same physical processes drive and occur in stellar flares as in solar flares. We tried to estimate the flare class by various direct and indirect methods. Light curves and spectra in different energy ranges were used to determine the parameters and profiles of the flare. From the XMM-Newton EPIC-pn X-ray data, we estimated the temperature and emission measure during the flare. The thermodynamical timescale and the loop semi-length were also determined with two different methods. The RGS spectra enabled us to calculate the differential emission measure (DEM) distributions. The obtained DEM distributions have three components at temperature values of 3, 7, and 16-17 MK. The analysis of the line ratio in helium-like triplets allowed us to determine the plasma electron density. Our results for the flare loop on Wolf 359 were compared to typical parameters for solar flares observed with GOES and RHESSI. This supports our conclusion that the processes taking place in stellar flares are like those in solar flares. The determined geometrical parameters of the phenomenon do not differ from the values of analogs occurring on the Sun.

Keywords: stellar flares; stellar activity; x-ray astronomy; stellar magnetic fields
Caught in the Act: A Metal-rich High-velocity Cloud in the Inner Galaxy

We characterize the chemical and physical conditions in an outflowing high-velocity cloud (HVC) in the inner Galaxy. We report a supersolar metallicity of [O/H] = +0.36 ± 0.12 for the HVC at v LSR = 125.6 km s-1 toward the star HD 156359 (l = 328.°7, b = -14.°5, d = 9 kpc, z = -2.3 kpc). Using archival observations from the Far-Ultraviolet Spectroscopic Explorer (FUSE), the Hubble Space Telescope Imaging Spectrograph, and the European Southern Observatory Fiber-fed Extended Range Optical Spectrograph we measure high-velocity absorption in H I, O I, C II, N II, Si II, Ca II, Si III, Fe III, C IV, Si IV, N V, and O VI. We measure a low H I column density of log N(H I) = 15.54 ± 0.05 in the HVC from multiple unsaturated H I Lyman series lines in the FUSE data. We determine a low dust depletion level in the HVC from the relative strength of silicon, iron, and calcium absorption relative to oxygen, with [Si/O] = -0.33 ± 0.14, [Fe/O] = -0.30 ± 0.20, and [Ca/O] = -0.56 ± 0.16. Analysis of the high-ion absorption using collisional ionization models indicates that the hot plasma is multiphase, with the C IV and Si IV tracing 104.9 K gas and N V and O VI tracing 105.4 K gas. The cloud's metallicity, dust content, kinematics, and close proximity to the disk are all consistent with a Galactic wind origin. As the HD 156359 line of sight probes the inner Galaxy, the HVC appears to be a young cloud caught in the act of being entrained in a multiphase Galactic outflow and driven out into the halo.

Keywords: galactic center; ultraviolet astronomy; high-velocity clouds; chemical abundances; galactic winds
An Application of the Global ILC Algorithm over Large Angular Scales to Estimate the CMB Posterior Using Gibbs Sampling

In this work, we formalize a new technique to investigate the joint posterior density of the cosmic microwave background (CMB) signal and its theoretical angular power spectrum given the observed data, using the global internal-linear-combination method first proposed in a paper by Sudevan & Saha in 2017. We implement the method on low-resolution CMB maps observed by the Wilkinson Microwave Anisotropy Probe (WMAP) and the Planck satellite missions, using Gibbs sampling, assuming that the detector noise is negligible on large angular scales of the sky. The main products of our analysis are a best-fit cleaned CMB map and its theoretical angular power spectrum, along with their error estimates. We validate the method by performing Monte Carlo simulations that include realistic foreground models and noise levels consistent with WMAP and Planck observations. Our method has a unique advantage: the posterior density is obtained without any need to explicitly model foreground components. Second, the power spectrum results with the error estimates can be directly used for cosmological parameter estimations.

Keywords: observational cosmology; diffuse radiation; cosmic microwave background radiation; gibbs sampler
On the Parameters of the Spherically Symmetric Parameterized Rezzolla-Zhidenko Spacetime through Solar System Tests, the Orbit of the S2 Star about Sgr A*, and Quasiperiodic Oscillations

In this paper, we find the higher-order expansion parameters α and λ of spherically symmetric parameterized Rezzolla-Zhidenko (PRZ) spacetime by using its functions of the radial coordinate. We subject the parameters of this spacetime to classical tests, including weak gravitational field effects in the solar system, observations of the S2 star that is located in the star cluster close to the Sgr A⋆, and of the frequencies of selected microquasars. Based on this spherically symmetric spacetime, we perform the analytic calculations for solar system effects such as perihelion shift, light deflection, and gravitational time delay to determine limits on the parameters by using observational data. We restrict our attention to the limits on the two higher-order expansion parameters α and λ that survive at the horizon or near the horizon of spherically symmetric metrics. The properties of the expansion of these two small parameters in PRZ parameterization are discussed. We further apply Markov Chain Monte Carlo simulations to analyze and obtain the limits on the expansion parameters by using observations of the phenomena of the S2 star. Finally, we consider the epicyclic motions and derive analytic expressions of the epicyclic frequencies. Applying these expressions to the quasiperiodic oscillations of selected microquasars allows us to set further limits on the parameters of the PRZ spacetime. Our results demonstrate that the higher-order expansion parameters can be given in the range α, λ = (-0.09, 0.09) and of order ~10-2 as a consequence of three different tests and observations.

Keywords: black holes; x-ray binary stars
Long Live the Disk: Lifetimes of Protoplanetary Disks in Hierarchical Triple-star Systems and a Possible Explanation for HD 98800 B

The gas dissipation from a protoplanetary disk is one of the key processes affecting planet formation, and it is widely accepted that it happens on timescales of a few million years for disks around single stars. In recent years, several protoplanetary disks have been discovered in multiple-star systems, and despite the complex environment in which they find themselves, some of them seem to be quite old, a situation that may favor planet formation. A clear example of this is the disk around HD 98800 B, a binary in a hierarchical quadruple stellar system, which at an ~10 Myr age seems to still be holding significant amounts of gas. Here we present a 1D+1D model to compute the vertical structure and gas evolution of circumbinary disks in hierarchical triple-star systems considering different stellar and disk parameters. We show that tidal torques due to the inner binary, together with the truncation of the disk due to the external companion, strongly reduce the viscous accretion and expansion of the disk. Even allowing viscous accretion by tidal streams, disks in these kind of environments can survive for more than 10 Myr, depending on their properties, with photoevaporation being the main gas dissipation mechanism. We particularly apply our model to the circumbinary disk around HD 98800 B and confirm that its longevity, along with the current nonexistence of a disk around the companion binary HD 98800 A, can be explained with our model and by this mechanism.

Keywords: protoplanetary disks