Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>The astronomical emission features, formerly known as the unidentified infrared bands, are now commonly ascribed to polycyclic aromatic hydrocarbons (PAHs). The laboratory experiments and computational modeling performed at NASA Ames Research Center generated a collection of PAH IR spectra that have been used to test and refine the PAH model. These data have been assembled into the NASA Ames PAH IR Spectroscopic Database (PAHdb). PAHdb’s library of computed spectra, currently at version 3.20, contains data on more than 4000 species and the library of laboratory-measured spectra, currently at version 3.00, contains data on 84 species. The spectra can be perused and are available for download at  <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="uri" xlink:href="http://www.astrochemistry.org/pahdb/" xlink:type="simple">www.astrochemistry.org/pahdb/</jats:ext-link>. This paper introduces the library of laboratory-measured spectra. Although it has been part of PAHdb since its inception, the library of laboratory-measured spectra lacked a proper description in the literature. Here, the experimental methods used to obtain the data are described in detail, an overview of the contents of the experimental library is given, and specific tools developed to analyze and interpret astronomical spectra with the laboratory data are discussed. In addition, updates to the website, documentation and software tools since our last reporting are presented. Software tools to work with the spectroscopic libraries are being developed actively and are available at GitHub. Lastly, a comprehensive demonstration showing how the laboratory-measured data can be applied to explore absorption features in observations toward embedded sources is presented. This demonstration suggests that PAHs very likely contribute to interstellar absorption spectra associated with dense clouds and underscores the need for further IR spectroscopic studies of PAHs trapped in water ice.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Studies of Galactic structure and evolution have benefited enormously from Gaia kinematic information, though additional, intrinsic stellar parameters like age are required to best constrain Galactic models. Asteroseismology is the most precise method of providing such information for field star populations en masse, but existing samples for the most part have been limited to a few narrow fields of view by the CoRoT and Kepler missions. In an effort to provide well-characterized stellar parameters across a wide range in Galactic position, we present the second data release of red giant asteroseismic parameters for the K2 Galactic Archaeology Program (GAP). We provide <jats:inline-formula> <jats:tex-math> <?CDATA ${\nu }_{\max }$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>ν</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>max</mml:mi> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjsabbee3ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> and <jats:inline-formula> <jats:tex-math> <?CDATA ${\rm{\Delta }}\nu $?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">Δ</mml:mi> <mml:mi>ν</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjsabbee3ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> based on six independent pipeline analyses; first-ascent red giant branch (RGB) and red clump (RC) evolutionary state classifications from machine learning; and ready-to-use radius and mass coefficients, <jats:italic>κ</jats:italic> <jats:sub> <jats:italic>R</jats:italic> </jats:sub> and <jats:italic>κ</jats:italic> <jats:sub> <jats:italic>M</jats:italic> </jats:sub>, which, when appropriately multiplied by a solar-scaled effective temperature factor, yield physical stellar radii and masses. In total, we report 4395 radius and mass coefficients, with typical uncertainties of 3.3% (stat.) ± 1% (syst.) for <jats:italic>κ</jats:italic> <jats:sub> <jats:italic>R</jats:italic> </jats:sub> and 7.7% (stat.) ± 2% (syst.) for <jats:italic>κ</jats:italic> <jats:sub> <jats:italic>M</jats:italic> </jats:sub> among RGB stars, and 5.0% (stat.) ± 1% (syst.) for <jats:italic>κ</jats:italic> <jats:sub> <jats:italic>R</jats:italic> </jats:sub> and 10.5% (stat.) ± 2% (syst.) for <jats:italic>κ</jats:italic> <jats:sub> <jats:italic>M</jats:italic> </jats:sub> among RC stars. We verify that the sample is nearly complete—except for a dearth of stars with <jats:inline-formula> <jats:tex-math> <?CDATA ${\nu }_{\max }\lesssim 10\mbox{--}20\,\mu \mathrm{Hz}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>ν</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>max</mml:mi> </mml:mrow> </mml:msub> <mml:mo>≲</mml:mo> <mml:mn>10</mml:mn> <mml:mo>–</mml:mo> <mml:mn>20</mml:mn> <mml:mspace width="0.25em" /> <mml:mi>μ</mml:mi> <mml:mi>Hz</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjsabbee3ieqn3.gif" xlink:type="simple" /> </jats:inline-formula>—by comparing to Galactic models and visual inspection. Our asteroseismic radii agree with radii derived from Gaia Data Release 2 parallaxes to within 2.2% ± 0.3% for RGB stars and 2.0% ± 0.6% for RC stars.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Analysis of hyperfine structure constants of singly ionized cobalt (Co II) were performed on cobalt spectra measured by Fourier transform spectrometers in the region 3000–63,000 cm<jats:sup>−1</jats:sup> (33333 – 1587 Å). Fits to over 700 spectral lines led to measurements of 292 magnetic dipole hyperfine interaction <jats:italic>A</jats:italic> constants, with values between −32.5 mK and 59.5 mK (1 mK = 0.001 cm<jats:sup>−1</jats:sup>). Uncertainties of 255 <jats:italic>A</jats:italic> constants were between ±0.4 mK and ±3.0 mK, the remaining 37 ranged up to ±7 mK. The electric quadrupole hyperfine interaction <jats:italic>B</jats:italic> constant could be estimated for only one energy level. The number of Co II levels with known <jats:italic>A</jats:italic> values has now increased tenfold, improving and enabling the wider, more reliable, and accurate application of Co II in astronomical chemical abundance analyses.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Magnetohydrodynamic (MHD) spectroscopy is central to many astrophysical disciplines, ranging from helio- to asteroseismology, over solar coronal (loop) seismology, to the study of waves and instabilities in jets, accretion disks, or solar/stellar atmospheres. MHD spectroscopy quantifies all linear (standing or traveling) wave modes, including overstable (i.e., growing) or damped modes, for a given configuration that achieves force and thermodynamic balance. Here, we present <jats:monospace>Legolas</jats:monospace>, a novel, open-source numerical code to calculate the full MHD spectrum of one-dimensional equilibria with flow, balancing pressure gradients, Lorentz forces, centrifugal effects, and gravity, and enriched with nonadiabatic aspects like radiative losses, thermal conduction, and resistivity. The governing equations use Fourier representations in the ignorable coordinates, and the set of linearized equations is discretized using finite elements in the important height or radial variation, handling Cartesian and cylindrical geometries using the same implementation. A weak Galerkin formulation results in a generalized (non-Hermitian) matrix eigenvalue problem, and linear algebraic algorithms calculate all eigenvalues and corresponding eigenvectors. We showcase a plethora of well-established results, ranging from <jats:italic>p</jats:italic> and <jats:italic>g</jats:italic> modes in magnetized, stratified atmospheres, over modes relevant for coronal loop seismology, thermal instabilities, and discrete overstable Alfvén modes related to solar prominences, to stability studies for astrophysical jet flows. We encounter (quasi-)Parker, (quasi-)interchange, current-driven, and Kelvin–Helmholtz instabilities, as well as nonideal quasi-modes, resistive tearing modes, up to magnetothermal instabilities. The use of high resolution sheds new light on previously calculated spectra, revealing interesting spectral regions that have yet to be investigated.</jats:p>