adsabs/SciX_UAT_keywords huggingface dataset:
The Nebula N103B in the LMC Contains Parts of Two Supernova Remnants

The nebula N103B in the Large Magellanic Cloud consists of a previously identified small diameter supernova remnant (SNR) on its northeastern edge and a bright eastern arc with a fainter western shell together covering a total of about 8 × 5' at the canonical distance of 50 kpc. The latter also has a nonthermal radio spectrum and is apparently another SNR. I propose that the small bright northeastern SNR be renamed N103B-NE and the newly identified large SNR be called N103B-extended.

Keywords: large magellanic cloud; supernova remnants; discrete radio sources
Distances, Radial Distribution, and Total Number of Galactic Supernova Remnants

We present a table of 215 supernova remnants (SNRs) with distances. New distances are found to SNR G51.26 + 0.11 of 6.6 ± 1.7 kpc using H I absorption spectra and to five other SNRs using maser/molecular cloud associations. We recalculate the distances and errors to all SNRs using a consistent rotation curve and provide errors where they were not previously estimated. This results in a significant distance revisions for 20 SNRs. Because of observational constraints and selection effects, there is an apparent deficit of observed number of Galactic SNRs. To investigate this, we employ two methods. The first method applies correction factors for the selection effects to derive the radial density distribution. The second method compares functional forms for the SNR surface density and selection function against the data to find which functions are consistent with the data. The total number of SNRs in the Galaxy is ~3500 (Method 1) or in the range from ~2400 to ~5600 (Method 2). We conclude that the current observed number of SNRs is not yet complete enough to give a well-determined total SNR number or radial density function.

Keywords: supernova remnants; radio astronomy; h i line emission; galaxy structure
List of the Close Asteroid Pairs Strongly Perturbed by Three-body Resonances

The two and three body mean motion resonances with Jupiter and Mars (and possible with Earth) may have a significant effect on the dynamics of very young close asteroid pairs and families. The best known example is the influence 9:16 resonance with Mars to some members of Datura family. It is evident, that the evolution of this family can be properly reconstructed only when this fact has been taken into account. One of the results of resonance perturbation may be the temporary compensation of the Yarkovsky drift in the semimajor axis. Studying this relationship may greatly improve the age estimation of asteroid pairs and families. In this note we give a list of some close asteroid pairs in the vicinity of mean motion resonances.

Keywords: celestial mechanics
Critical Mach Numbers for Magnetohydrodynamic Shocks with Accelerated Particles and Waves

The first critical fast Mach number is defined for a magnetohydrodynamic shock as the Mach number where the shock transitions from subcritical, laminar behavior to supercritical behavior, characterized by incident ion reflection from the shock front. The ensuing upstream waves and turbulence are convected downstream, leading to a turbulent shock structure. Formally, this is the Mach number where plasma resistivity can no longer provide sufficient dissipation to establish a stable shock, and is characterized by the downstream flow speed becoming subsonic. We revisit these calculations, including in the MHD jump conditions terms modeling the plasma energy loss to accelerated particles and the presence of waves associated with these particles. The accelerated particle contributions make an insignificant change, but the associated waves have a more important effect. Upstream waves can be strongly amplified in intensity on passing through the shock, and they represent another means of shock dissipation. The presence of such waves therefore increases the first critical fast Mach number, especially at quasi-parallel shock where wave excitation is strongest. These effects may have significance for the solar regions where shock waves accelerate particles and cause Type II and Type III radio bursts, and they could also contribute to the event-to-event variability of SEP acceleration.

Keywords: solar coronal mass ejection shocks; solar energetic particles; interplanetary particle acceleration; alfven waves
Accumulation of Elastic Strain toward Crustal Fracture in Magnetized Neutron Stars

This study investigates elastic deformation driven by the Hall drift in a magnetized neutron-star crust. Although the dynamic equilibrium initially holds without elastic displacement, the magnetic-field evolution changes the Lorentz force over a secular timescale, which inevitably causes the elastic deformation to settle in a new force balance. Accordingly, elastic energy is accumulated, and the crust is eventually fractured beyond a particular threshold. We assume that the magnetic field is axially symmetric, and we explicitly calculate the breakup time, maximum elastic energy stored in the crust, and spatial shear-stress distribution. For the barotropic equilibrium of a poloidal dipole field expelled from the interior core without a toroidal field, the breakup time corresponds to a few years for the magnetars with a magnetic-field strength of ~1015 G; however, it exceeds 1 Myr for normal radio pulsars. The elastic energy stored in the crust before the fracture ranges from 1041 to 1045 erg, depending on the spatial-energy distribution. Generally, a large amount of energy is deposited in a deep crust. The energy released at a fracture is typically ~1041 erg when the rearrangement of elastic displacements occurs only in the fragile shallow crust. The amount of energy is comparable to the outburst energy on the magnetars.

Keywords: neutron stars; magnetars; compact objects; high energy astrophysics; magnetic fields; soft gamma-ray repeaters
A Variant Stellar-to-nebular Dust Attenuation Ratio on Subgalactic and Galactic Scales

The state-of-the-art geometry models of stars/dust suggest that dust attenuation toward nebular regions ( ${A}_{V,\mathrm{gas}}$ ) is always larger than that of stellar regions ( ${A}_{V,\mathrm{star}}$ ). Utilizing the newly released integral field spectroscopic data from the Mapping Nearby Galaxies at Apache Point Observatory survey, we investigate whether and how the ${A}_{V,\mathrm{star}}/{A}_{V,\mathrm{gas}}$ ratio varies from subgalactic to galactic scales. On a subgalactic scale, we report a stronger correlation between ${A}_{V,\mathrm{star}}$ and ${A}_{V,\mathrm{gas}}$ for more active H II regions. The local ${A}_{V,\mathrm{star}}/{A}_{V,\mathrm{gas}}$ is found to have moderate nonlinear correlations with three tracers of diffuse ionized gas (DIG), as well as indicators of gas-phase metallicity and ionization. The DIG regions tend to have larger ${A}_{V,\mathrm{star}}/{A}_{V,\mathrm{gas}}$ compared to classic H II regions excited by young OB stars. Metal-poor regions with a higher ionized level suffer much less nebular attenuation and thus have larger ${A}_{V,\mathrm{star}}/{A}_{V,\mathrm{gas}}$ ratios. A low- ${A}_{V,\mathrm{gas}}$ and high- ${A}_{V,\mathrm{star}}/{A}_{V,\mathrm{gas}}$ sequence, which can be resolved into DIG-dominated and metal-poor regions, on the three BPT diagrams is found. Based on these observations, we suggest that besides the geometry of stars/dust, local physical conditions such as metallicity and ionized level also play an important role in determining the ${A}_{V,\mathrm{star}}/{A}_{V,\mathrm{gas}}$ . On a galactic scale, the global ${A}_{V,\mathrm{star}}/{A}_{V,\mathrm{gas}}$ ratio has strong correlations with stellar mass (M*), moderate correlations with star formation rate (SFR) and metallicity, and weak correlations with inclination and specific SFR. Galaxies with larger M* and higher SFR that are more metal-rich tend to have smaller ${A}_{V,\mathrm{star}}/{A}_{V,\mathrm{gas}}$ ratios. Such correlations form a decreasing trend of ${A}_{V,\mathrm{star}}/{A}_{V,\mathrm{gas}}$ along the star-forming main sequence and mass-metallicity relation. The dust growth process accompanied by galaxy growth might be one plausible explanation for our observations.

Keywords: interstellar dust extinction; galaxy evolution; interstellar medium; warm ionized medium; h ii regions
Impact of Planetary Mass Uncertainties on Exoplanet Atmospheric Retrievals

In current models used to interpret exoplanet atmospheric observations, the planetary mass is treated as a prior and is measured/estimated independently with external methods, such as radial velocity or transit timing variation techniques. This approach is necessary as available spectroscopic data do not have sufficient wavelength coverage and/or signal-to-noise to infer the planetary mass. We examine here whether the planetary mass can be directly retrieved from transit spectra as observed by future space observatories, which will provide higher quality spectra. More in general, we quantify the impact of mass uncertainties on spectral retrieval analyses for a host of atmospheric scenarios. Our approach is both analytical and numerical: we first use simple approximations to extract analytically the influence of each atmospheric/planetary parameter to the wavelength-dependent transit depth. We then adopt a fully Bayesian retrieval model to quantify the propagation of the mass uncertainty onto other atmospheric parameters. We found that for clear-sky, gaseous atmospheres the posterior distributions are the same when the mass is known or retrieved. The retrieved mass is very accurate, with a precision of more than 10%, provided the wavelength coverage and signal-to-noise ratio are adequate. When opaque clouds are included in the simulations, the uncertainties in the retrieved mass increase, especially for high altitude clouds. However, atmospheric parameters such as the temperature and trace-gas abundances are unaffected by the knowledge of the mass. Secondary atmospheres, expected to be present in many super-Earths, are more challenging due to the higher degree of freedom for the atmospheric main component, which is unknown. For broad wavelength range and adequate signal-to-noise observations, the mass can still be retrieved accurately and precisely if clouds are not present, and so are all the other atmospheric/planetary parameters. When clouds are added, we find that the mass uncertainties may impact substantially the retrieval of the mean molecular weight: an independent characterization of the mass would therefore be helpful to capture/confirm the main atmospheric constituent.

Keywords: exoplanet atmospheres
Stochastic Parker Spirals in the Solar Wind

An analytic model for the angular dispersion of magnetic field lines resulting from the turbulence in the solar wind and at the solar source surface is presented. The heliospheric magnetic field lines in our model are derived from a Hamiltonian ${H}_{{\rm{m}}}(\mu ,\phi ,r)$ with the pair of canonically conjugated variables the cosine of the heliographic colatitude μ and the longitude φ. In the diffusion approximation, the Parker spirals are modeled by a set of stochastic differential equations for θ and φ as functions of r. These stochastic Parker spirals are realizations of a standard random walk on a sphere of increasing radius, superimposed on an angular drift due to solar rotation. The Green function solution of the Fokker-Planck equation describing the angular diffusion of the field line density is obtained in terms of spherical harmonics. Magnetic field lines traced from an observer back to the Sun are realizations of a Brownian bridge. Our model incorporates the effect of the random footpoint motions at the source surface, which is associated with the zero-frequency component of the solar wind turbulence. Assuming that the footpoint motion is diffusive, its contribution to the angular diffusivity of the stochastic Parker spirals is then given by the angular diffusivity of the footpoints divided by the solar wind speed and is controlled by a unique parameter, which is the Kubo number.

Keywords: solar flares; interplanetary magnetic fields; interplanetary turbulence
Investigating the Time Evolution of the Thermal Emission from the Putative Neutron Star in SN 1987A for 50+ Years

Observations collected with the Atacama Large Millimeter/submillimeter Array (ALMA) and analysis of broadband X-ray spectra have recently suggested the presence of a central compact object (CCO) in SN 1987A. However, no direct evidence of the CCO has been found yet. Here we analyze Chandra X-ray observations of SN 1987A collected in 2007 and 2018, and synthesize 2027 Chandra and 2037 Lynx spectra of the faint inner region of SN 1987A. We estimate the temporal evolution of the upper limits of the intrinsic luminosity of the putative CCO in three epochs (2018, 2027, and 2037). We find that these upper limits are higher for higher neutron star (NS) kick velocities due to increased absorption from the surrounding cold ejecta. We compare NS cooling models with both the intrinsic luminosity limits obtained from the X-ray spectra and the ALMA constraints with the assumption that the observed blob of SN 1987A is primarily heated by thermal emission. We find that the synthetic Lynx spectra are crucial to constrain the physical properties of the CCO, which will be confirmed by future observations in the 2040s. We draw our conclusions based on two scenarios, namely the nondetection and detection of the NS by Lynx. If the NS is not detected, its kick velocity should be ≃700 km s-1. Furthermore, nondetection of the NS would suggest rapid cooling processes at the age of 40 yr, implying strong crust superfluidity. Conversely, in the case of NS detection, the mass of the NS envelope must be high.

Keywords: supernovae; neutron stars; supernova remnants; compact objects; x-ray astronomy; x-ray sources
The Impact of Multifluid Effects in the Solar Chromosphere on the Ponderomotive Force under SE and NEQ Ionization Conditions

The ponderomotive force has been suggested to be the main mechanism to produce the so-called first ionization potential (FIP) effect-the enrichment of low-FIP elements observed in the outer solar atmosphere, in the solar wind, and in solar energetic events. It is well known that the ionization of these elements occurs within the chromosphere. Therefore, this phenomenon is intimately tied to the plasma state in the chromosphere and the corona. For this study, we combine IRIS observations, a single-fluid 2.5D radiative magnetohydrodynamics (MHD) model of the solar atmosphere, including ion-neutral interaction effects and nonequilibrium (NEQ) ionization effects, and a novel multifluid multispecies numerical model (based on the Ebysus code). Nonthermal velocities of Si IV measured from IRIS spectra can provide an upper limit for the strength of any high-frequency Alfvén waves. With the single-fluid model, we investigate the possible impact of NEQ ionization within the region where the FIP may occur, as well as the plasma properties in those regions. These models suggest that regions with strongly enhanced network and type II spicules are possible sites of large ponderomotive forces. We use the plasma properties of the single-fluid MHD model and the IRIS observations to initialize our multifluid models to investigate the multifluid effects on the ponderomotive force associated with Alfvén waves. Our multifluid analysis reveals that collisions and NEQ ionization effects dramatically impact the behavior of the ponderomotive force in the chromosphere, and existing theories may need to be revisited.

Keywords: solar atmosphere; solar corona; solar abundances; stellar coronae; solar chromosphere; stellar physics; stellar atmospheres; solar spicules; solar magnetic fields
Empirical Test for Relativistic Kinetic Theories Based on the Sunyaev-Zel'dovich Effect

We propose a new method to determine the electron velocity (EV) distribution function in the intracluster gas (ICG) in clusters of galaxies based on the frequency dependence of the Sunyaev-Zel'dovich (SZ) effect. It is generally accepted that the relativistic equilibrium EV distribution is the one suggested by Jüttner. However, there is an ongoing debate on the foundation of relativistic kinetic theory, and other distributions have also been proposed. The mildly relativistic ICG provides a unique laboratory to test relativistic kinetic theories. We carried out Monte Carlo simulations to generate SZ signal from a single-temperature gas assuming the Jüttner EV distribution assuming a few percent errors. We fitted SZ models based on nonrelativistic Maxwellian, and its two relativistic generalizations, the Jüttner and modified Jüttner distributions. We found that a 1% error in the SZ signal is sufficient to distinguish between these distributions with high significance based on their different best-fit temperatures. However, in any line of sight (LOS) in a cluster, the ICG contains a range of temperatures. Using our N-body/hydrodynamical simulation of a merging galaxy cluster and assuming a 1% error in the SZ measurements in an LOS through a bow shock, we find that it is possible to distinguish between Jüttner and modified Jüttner distributions with high significance. Our results suggest that deriving ICG temperatures from fitting to SZ data assuming different EV distribution functions and comparing them to the temperature in the same cluster obtained using other observations would enable us to distinguish between the different distributions.

Keywords: galaxy clusters; sunyaev-zeldovich effect
GRB Afterglow of the Sub-relativistic Materials with Energy Injection

Sub-relativistic materials launched during the merger of binary compact objects and the core collapse of massive stars acquire velocity structures when expanding in a stratified environment. The remnant (either a spinning magnetized neutron star (NS) or a central black hole) from the compact object or core collapse could additionally inject energy into the afterglow via spin-down luminosity or/and by accreting fallback material, producing a refreshed shock, modifying the dynamics, and leading to rich radiation signatures at distinct timescales and energy bands with contrasting intensities. We derive the synchrotron light curves evolving in a stratified environment when a power-law velocity distribution parameterizes the energy of the shock, and the remnant continuously injects energy into the blast wave. As the most relevant case, we describe the latest multiwavelength afterglow observations (≳900 days) of the GW170817/GRB 170817A event via a synchrotron afterglow model with energy injection of a sub-relativistic material. The features of the remnant and the synchrotron emission of the sub-relativistic material are consistent with a spinning magnetized NS and the faster blue kilonova afterglow, respectively. Using the multiband observations of some short bursts with evidence of kilonovae, we provide constraints on the expected afterglow emission.

Keywords: gamma-ray bursts; non-thermal radiation sources
Evidence of First Stars-enriched Gas in High-redshift Absorbers

The first stars were born from chemically pristine gas. They were likely massive, and thus they rapidly exploded as supernovae, enriching the surrounding gas with the first heavy elements. In the Local Group, the chemical signatures of the first stellar population were identified among low-mass, long-lived, very metal-poor ([Fe/H] < -2) stars, characterized by high abundances of carbon over iron ([C/Fe] > +0.7): the so-called carbon-enhanced metal-poor stars. Conversely, a similar carbon excess caused by first-star pollution was not found in dense neutral gas traced by absorption systems at different cosmic time. Here we present the detection of 14 very metal-poor, optically thick absorbers at redshift z ~ 3-4. Among these, 3 are carbon-enhanced and reveal an overabundance with respect to Fe of all the analyzed chemical elements (O, Mg, Al, and Si). Their relative abundances show a distribution with respect to [Fe/H] that is in very good agreement with those observed in nearby very metal-poor stars. All the tests we performed support the idea that these C-rich absorbers preserve the chemical yields of the first stars. Our new findings suggest that the first-star signatures can survive in optically thick but relatively diffuse absorbers, which are not sufficiently dense to sustain star formation and hence are not dominated by the chemical products of normal stars.

Keywords: chemical abundances; quasar absorption line spectroscopy; metallicity
The Empirical and Radiative Transfer Hybrid (EaRTH) Disk Model: Merging Analyses of Protoplanetary Dust Disk Mineralogy and Structure

Our understanding of how exoplanets form and evolve relies on analyses of both the mineralogy of protoplanetary disks and their detailed structures; however, these key complementary aspects of disks are usually studied separately. We present initial results from a hybrid model that combines the empirical characterization of the mineralogy of a disk, as determined from its mid-infrared spectral features, with the MCFOST radiative transfer disk model, a combination we call the Empirical and Radiative Transfer Hybrid (EaRTH) Disk Model. With the results of the mineralogy detection serving as input to the radiative transfer model, we generate mid-infrared spectral energy distributions (SEDs) that reflect both the mineralogical and structural parameters of the corresponding disk. Initial fits of the SED output by the resulting integrated model of Spitzer Space Telescope mid-infrared spectra of the protoplanetary disk orbiting the nearby T Tauri star MP Mus demonstrate the potential advantages of this approach by revealing details like the dominance of micron-sized olivine and micron-sized forsterite in this dusty disk. The simultaneous insight into disk composition and structure provided by the EaRTH Disk methodology should be directly applicable to the interpretation of mid-infrared spectra of protoplanetary disks that will be produced by the James Webb Space Telescope.

Keywords: protoplanetary disks; circumstellar dust; dust composition; young stellar objects
The Ultraviolet Spectra of Alpha Draconis Recorded by IUE

The comparison of all unpublished archival IUE spectra of the bright spectroscopic binary α Draconis shows that the far-ultraviolet flux has remained constant over the 18 yr of the mission, except possibly for one spectrum which shows significantly less flux below 1800 Å. The Si II lines undergo large radial velocity variations which are due to the orbital motion of α Draconis around the center of mass of the system. The far-UV energy distribution of α Draconis has more flux than that of Sirius A (α CMa) which reflects the weaker abundances of the metals in α Draconis compared to Sirius A.

Keywords: a giant stars