Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>We develop the theoretical basis for the connection of the variety of anisotropic distributions with the statistical correlations among particles’ velocity components. By examining the most common anisotropic distribution function, we derive the correlation coefficient among particle energies, show how this correlation is connected to the effective dimensionality of the velocity distribution, and derive the connection between anisotropy and adiabatic polytropic index. Having established the importance of the correlation among particles in the formulation of anisotropic kappa distributions, we generalize these distributions within the framework of nonextensive statistical mechanics and based on the types of homogeneous or heterogeneous correlations among the particles’ velocity components. The formulation of the developed generalized distributions mediates the main two types of anisotropic kappa distributions that consider either (a) equal correlations, or (b) zero correlations, among different velocity components. Finally, the developed anisotropic kappa distributions are expressed in terms of the energy and pitch angle in arbitrary reference frames.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A morphological search for molecular shells and cavities was performed around 63 Galactic supernova remnants (SNRs) at 10° ≤ <jats:italic>l</jats:italic> ≤ 50°, ∣<jats:italic>b</jats:italic>∣ ≤ 1° using the FOREST Unbiased Galactic Imaging survey with the Nobeyama 45 m telescope CO-line data at high-angular (20″) and high-velocity (1.3 km s<jats:sup>−1</jats:sup>) resolutions. The results are presented as supplementary data for general purpose investigations of the interaction between SNRs and interstellar matter in the form of an atlas of CO-line maps superposed on radio continuum maps at 20 cm along with a list of their kinematic distances determined from CO-line radial velocities.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present an efficient algorithm to follow spectral evolution of cosmic rays (CR) coupled with an MHD system on Eulerian grids. The algorithm is designed for studies of CR energy spectrum evolution in MHD simulations of a galactic interstellar medium. The base algorithm for CR transport relies on the two-moment piece-wise power-law method, known also as coarse-grained momentum finite volume (CGMV), for solving the Fokker–Planck CR transport equation, with a low number of momentum bins extending over several decades of the momentum coordinate. We propose an extension of the CGMV with a novel feature that allows momentum boundaries to change in response to CR momentum gains or losses near the extremes of the population distribution. Our extension involves a special treatment of momentum bins containing spectral cutoff. Contrary to the regular bins of fixed width, those bins have variable width, and their outer edges coincide with spectral cutoffs. The cutoff positions are estimated from the particle number density and energy density in the outer bins for an assumed small value of an additional parameter representing the smallest physically significant level of CR spectral energy density. We performed a series of elementary tests to validate the algorithm and demonstrated, whenever possible, that results of the test simulations correspond, with a reasonable accuracy, to the results of analogous analytical solutions. In a more complex test of the galactic CR-driven wind problem, we obtained results consistent with expectations regarding the effects of advection, diffusion, adiabatic, and synchrotron cooling of a CR population.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We have used the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) low-resolution and medium-resolution spectroscopic surveys to explore the chromospheric statistical properties and variations of M stars. There are 738,477 LAMOST low-resolution spectra of 622,523 M stars. We have calculated equivalent widths of the Ca <jats:sc>ii</jats:sc> H&amp;K, H<jats:italic>α</jats:italic>, H<jats:italic>β</jats:italic>, H<jats:italic>γ</jats:italic>, H<jats:italic>δ</jats:italic>, He <jats:sc>i</jats:sc> D3, and Ca <jats:sc>ii</jats:sc> infrared triplet lines. Based on the H<jats:italic>α</jats:italic> EWs, we found that 33,374 objects showed H<jats:italic>α</jats:italic> emissions. We revised the relationship between the active fraction and spectral subtype, and confirmed that the active fractions increased from M0 to M3, and possibly declined from M4 to subsequent types. Among 86,005 objects with repeated spectra, 19,422 objects showed H<jats:italic>α</jats:italic> variations. The variation fraction of stars with M4 and subsequent types with a fully convective envelope was higher than those of M0–M3 with a partially convective envelope. By combining the distances from Gaia, we have determined the positions of the M dwarfs in the catalog for M stars. The active fraction decreased rapidly in the height range of 0–400 pc above and below the Galactic plane, and maintained a steady trend in 400–1000 pc. We cross-matched the M catalog of the LAMOST low-resolution survey with LAMOST medium-resolution spectra. We obtained 272,181 spectra of 13,355 M objects and calculated the H<jats:italic>α</jats:italic> EWs. Among them, 3813 stars show variations, which might be caused by chromospheric activity evolution with orbital phase or time. The H<jats:italic>α</jats:italic> emission for 972 objects shows variations over short and long timescales, especially on short timescales of 20 minutes.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In this work, we present the first results of the long-term high-cadence spectroscopic monitoring of 15 PG quasars with relatively strong Fe <jats:sc>ii</jats:sc> emission, as a part of a broader reverberation mapping campaign performed using the Calar Alto Observatory’s 2.2 m telescope. The <jats:italic>V</jats:italic>-band, 5100 Å continuum, and H<jats:italic>β</jats:italic> broad emission line light curves are measured for a set of quasars for periods ranging from dozens to more than a hundred epochs between 2017 May and 2020 July. Accurate time lags between the variations of the H<jats:italic>β</jats:italic> broad-line fluxes and the optical continuum strength are obtained for all 15 quasars, ranging from <jats:inline-formula> <jats:tex-math> <?CDATA ${17.0}_{-3.2}^{+2.5}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>17.0</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3.2</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>2.5</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjsabd774ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> to <jats:inline-formula> <jats:tex-math> <?CDATA ${95.9}_{-23.9}^{+7.1}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>95.9</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>23.9</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>7.1</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjsabd774ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> days in the rest frame. The virial masses of the central supermassive black holes are derived for all 15 quasars, ranging between <jats:inline-formula> <jats:tex-math> <?CDATA ${0.50}_{-0.19}^{+0.18}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>0.50</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.19</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.18</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjsabd774ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> and <jats:inline-formula> <jats:tex-math> <?CDATA ${19.17}_{-2.73}^{+2.98}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>19.17</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2.73</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>2.98</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjsabd774ieqn4.gif" xlink:type="simple" /> </jats:inline-formula> in units of 10<jats:sup>7</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. For 11 of the objects in our sample, this is the first reverberation analysis to be published. Of the rest, two objects have been the subject of previous reverberation studies, but we determine time lags for these that are only half as long as those found in the earlier investigations, which had only been able to sample much more sparsely. The remaining two objects have previously been monitored with high sampling rates. Our results here are consistent with the earlier findings, in the sense that the time lag and the line width vary inversely, consistent with virialization.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>This paper describes algorithms for nonrelativistic hydrodynamics in the toolkit for high-order neutrino radiation hydrodynamics (<jats:monospace>thornado</jats:monospace>), which is being developed for multiphysics simulations of core-collapse supernovae (CCSNe) and related problems with Runge–Kutta discontinuous Galerkin (RKDG) methods. More specifically, <jats:monospace>thornado</jats:monospace> employs a spectral-type nodal collocation approximation, and we have extended limiters—a slope limiter to prevent nonphysical oscillations and a bound-enforcing limiter to prevent nonphysical states—from the standard RKDG framework to be able to accommodate a tabulated nuclear equation of state (EoS). To demonstrate the efficacy of the algorithms with a nuclear EoS, we first present numerical results from basic test problems in idealized settings in one and two spatial dimensions, employing Cartesian, spherical-polar, and cylindrical coordinates. Then, we apply the RKDG method to the problem of adiabatic collapse, shock formation, and shock propagation in spherical symmetry, initiated with a 15 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> progenitor. We find that the extended limiters improve the fidelity and robustness of the RKDG method in idealized settings. The bound-enforcing limiter improves the robustness of the RKDG method in the adiabatic collapse application, while we find that slope limiting in characteristic fields is vulnerable to structures in the EoS—more specifically, in the phase transition from nuclei and nucleons to bulk nuclear matter. The success of these applications marks an important step toward applying RKDG methods to more realistic CCSN simulations with <jats:monospace>thornado</jats:monospace> in the future.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a data-driven method to estimate absolute magnitudes for O- and B-type stars from the LAMOST spectra, which we combine with Gaia DR2 parallaxes to infer distance and binarity. The method applies a neural network model trained on stars with precise Gaia parallax to the spectra and predicts <jats:italic>K</jats:italic> <jats:sub>s</jats:sub>-band absolute magnitudes <jats:inline-formula> <jats:tex-math> <?CDATA ${M}_{K{\rm{s}}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjsabd6baieqn1.gif" xlink:type="simple" /> </jats:inline-formula> with a precision of 0.25 mag, which corresponds to a precision of 12% in spectroscopic distance. For distant stars (e.g., &gt;5 kpc), the inclusion of constraints from spectroscopic <jats:inline-formula> <jats:tex-math> <?CDATA ${M}_{K{\rm{s}}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjsabd6baieqn2.gif" xlink:type="simple" /> </jats:inline-formula> significantly improves the distance estimates compared to inferences from Gaia parallax alone. Our method accommodates for emission-line stars by first identifying them via principal component analysis reconstructions and then treating them separately for the <jats:inline-formula> <jats:tex-math> <?CDATA ${M}_{K{\rm{s}}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjsabd6baieqn3.gif" xlink:type="simple" /> </jats:inline-formula> estimation. We also take into account unresolved binary/multiple stars, which we identify through deviations in the spectroscopic <jats:inline-formula> <jats:tex-math> <?CDATA ${M}_{K{\rm{s}}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjsabd6baieqn4.gif" xlink:type="simple" /> </jats:inline-formula> from the geometric <jats:inline-formula> <jats:tex-math> <?CDATA ${M}_{K{\rm{s}}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjsabd6baieqn5.gif" xlink:type="simple" /> </jats:inline-formula> inferred from Gaia parallax. This method of binary identification is particularly efficient for unresolved binaries with near equal-mass components and thus provides a useful supplementary way to identify unresolved binary or multiple-star systems. We present a catalog of spectroscopic <jats:inline-formula> <jats:tex-math> <?CDATA ${M}_{K{\rm{s}}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjsabd6baieqn6.gif" xlink:type="simple" /> </jats:inline-formula>, extinction, distance, flags for emission lines, and binary classification for 16,002 OB stars from LAMOST DR5. As an illustration, we investigate the <jats:inline-formula> <jats:tex-math> <?CDATA ${M}_{K{\rm{s}}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjsabd6baieqn7.gif" xlink:type="simple" /> </jats:inline-formula> of the enigmatic LB-1 system, which Liu et al. had argued consists of a B star and a massive stellar-mass black hole. Our results suggest that LB-1 is a binary system that contains two luminous stars with comparable brightness, and the result is further supported by parallax from the Gaia eDR3.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Milky Way contains thousands of H <jats:sc>ii</jats:sc> region candidates identified by their characteristic mid-infrared morphology, but lacking detections of ionized gas tracers such as radio continuum or radio recombination line emission. These targets thus remain unconfirmed as H <jats:sc>ii</jats:sc> regions. With only ∼2500 confirmed H <jats:sc>ii</jats:sc> regions in the Milky Way, Galactic surveys are deficient by several thousand nebulae when compared to external galaxies with similar star formation rates. Using sensitive 9 GHz radio continuum observations with the Karl G. Jansky Very Large Array, we explore a sample of H <jats:sc>ii</jats:sc> region candidates in order to set observational limits on the actual total population of Galactic H <jats:sc>ii</jats:sc> regions. We target all infrared–identified “radio-quiet” sources from the Wide-field Infrared Survey Explorer Catalog of Galactic H <jats:sc>ii</jats:sc> regions between 245° ≥ <jats:italic>ℓ</jats:italic> ≥ 90° with infrared diameters less than 80<jats:sup>′′</jats:sup>. We detect radio continuum emission from 50% of the targeted H <jats:sc>ii</jats:sc> region candidates, providing strong evidence that most of the radio-quiet candidates are bona fide H <jats:sc>ii</jats:sc> regions. We measure the peak and integrated radio flux densities and compare the inferred Lyman continuum fluxes using models of OB stars. We conclude that stars of approximately spectral type B2 and earlier are able to create H <jats:sc>ii</jats:sc> regions with similar infrared and radio continuum morphologies as the more luminous H <jats:sc>ii</jats:sc> regions created by O stars. From our 50% detection rate of “radio-quiet” sources, we set a lower limit of ∼7000 for the H <jats:sc>ii</jats:sc> region population of the Galaxy. Thus the vast majority of the Milky Way’s H <jats:sc>ii</jats:sc> regions remain to be discovered.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The goal of the present work is to solve the magnetohydrodynamic (MHD) system of extended generalized Lagrange multiplier (EGLM) formulation with Galilean invariance (G-EGLM MHD equations) through a modified path-conservative HLLEM finite-volume method. A second-order least-squares reconstruction with Venkatakrishnan limiter is employed for state variables, and a solenoidality-preserving condition is considered for the magnetic field with the purpose of magnetic divergence cleaning. The two-stage Runge–Kutta time-integration method is utilized to advance the MHD governing equations. Compared with the original path-conservative HLLEM method, the modified method in this paper is shock stable and is able to adjust the diffusion according to the smoothness of the physical flow so as to automatically apply more diffusion near strong shocks and less in smooth regions near rarefaction waves and at contact discontinuities. Meanwhile, it can be robustly defined in the low plasma-<jats:italic>β</jats:italic> region. After several tests of smooth Alfvén wave, strong Lax, odd–even perturbation, and blast-wave problems, the large-scale structures of the solar corona for Carrington Rotation 2185 are numerically modeled in a six-component grid system of spherical coordinates with input from a Carrington rotation synoptic map provided by the Helioseismic and Magnetic Imager. Numerical results show the model’s capability of producing a structured solar wind in agreement with the observations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the largest sample of giant radio quasars (GRQs), which are defined as having a projected linear size greater than 0.7 Mpc. The sample consists of 272 GRQs, of which 174 are new objects discovered through cross-matching the NRAO Very Large Array Sky Survey and the Sloan Digital Sky Survey 14th Data Release Quasar Catalog (DR14Q) and confirmed using Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) radio maps. In our analysis we compare the GRQs with 367 smaller, lobe-dominated radio quasars found using our search method, as well as with quasars from the SDSS DR14Q, investigating the parameters characterizing their radio emission (i.e., total and core radio luminosity, radio core prominence), optical properties (black hole masses, accretion rates, distribution in Eigenvector 1 plane) and infrared colors. For the GRQs and smaller radio quasars we find a strong correlation between [O <jats:sc>III</jats:sc>] luminosity and radio luminosity at 1.4 GHz, indicating a strong connection between radio emission and conditions in the narrow-line region. We spot no significant differences between GRQs and smaller radio quasars, however we show that most extended radio quasars belong to a quasar population of evolved active galactic nuclei with large black hole masses and low accretion rates. We also show that GRQs have bluer W2–W3 colors compared to SDSS quasars with FIRST detections, indicating differences in the structure of the dusty torus.</jats:p>