Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>We present a comprehensive model of the ground-based polarization observations from comet 67P/Churyumov–Gerasimenko using two different apertures on its apparitions of 1982 and 2016. Our modeling suggests that the dust composition viewed within the two apertures is the same, but that they have different size distributions, with smaller particles more concentrated in the innermost coma. The best fits to the measurements using the smallest aperture are obtained using a dust size distribution similar to the Rosetta findings. Furthermore, the model parameters providing the best fit to polarimetric observations using the large aperture appear remarkably consistent with what was previously inferred in other comets. This represents an attempt to reconcile the Rosetta results with ground-based observations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Since antiquity, people have observed the night sky. To establish order and predictability, people made maps of the heavens. Two kinds emerged. The first were star maps, organized into constellations but focused on stellar location in the sky. Stars were placed in a coordinate system, initially based on celestial latitude and longitude oriented to the ecliptic, but later based on decl. and R.A. oriented to the celestial equator. Over time, telescopic and scientific needs called for more detailed coordinate systems, and constellation images disappeared. The second kind of heavenly map depicted the solar system and focused on planetary locations and surface characteristics. For many centuries, these were cosmological diagrams with concentric planetary and stellar circles, centered first on the Earth and then the Sun. Now such maps have no stellar boundary, and ever larger telescopes and space probes allow us to view planetary surfaces in unprecedented detail.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present Very Large Array cm continuum observations, as well as 1.3 mm continuum and CO(2–1) observations taken with the Submillimeter Array toward the high-mass protostellar candidate ISOSS J23053+5953 SMM2. Compact cm continuum emission was detected near the center of the SMM2 dust core, and the 1.3 mm thermal dust emission indicates a core mass of 46  <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. The CO(2–1) observation revealed a large, massive molecular flow centered on the SMM2 core. This fast outflow (&gt;50 km s<jats:sup>−1</jats:sup>) appears highly collimated, with a broader, lower-velocity component. The large values for outflow mass (45 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>), and energetics derived are consistent with those of flows driven by high-mass YSOs. The dynamical timescale of the flow is between 1.5−7.2 × 10<jats:sup>4</jats:sup> yr. Our data confirm previous findings that SMM2 is an emerging high-mass protostar in a very early phase of evolution, with an ionized jet, and a fast, highly collimated, and massive outflow.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Many astrophysical environments involve convective or explosive flows driven by thermonuclear reactions (Type Ia supernovae, classical novae, X-ray bursts, stellar evolution). Simulation codes need to accurately capture the interactions between reactions and hydrodynamics to produce realistic models of these events. For astrophysical reacting flows, operator splitting is commonly used to couple hydrodynamics and reactions. Each process operates independent of one another, but by staggering the updates in a symmetric fashion (via Strang splitting) second order accuracy in time can be achieved. However, approximations are often made to the reacting system, including the choice of whether or not to integrate temperature with the species. Here we demonstrate through a simple convergence test that integrating an energy equation together with reactions achieves the best convergence when modeling reactive flows with Strang splitting. Additionally, second order convergence cannot be achieved without integrating an energy or temperature equation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We examine Hubble Space Telescope (HST)/STIS data, complemented with International Ultraviolet Explorer (IUE) data, to delineate interstellar absorption of highly ionized species, C <jats:sc>iv</jats:sc>, Si <jats:sc>iv</jats:sc>, and N <jats:sc>v</jats:sc>, and low ionization species toward four stars in Cygnus. Previous IUE studies indicate two major velocity complexes for C <jats:sc>iv</jats:sc> and Si <jats:sc>iv</jats:sc> extending across Cygnus. We see interstellar N <jats:sc>v</jats:sc> in HST/STIS data for HD 190918 and Cyg X-1. In both stars, the N <jats:sc>v</jats:sc> is at the velocities of interstellar C <jats:sc>iv</jats:sc> and Si <jats:sc>iv</jats:sc>. In HD 190918, the N <jats:sc>v</jats:sc> is weak, possibly due to enhanced X-ray ionization produced by this binary system. The Cyg X-1 data are of low signal-to-noise, but N <jats:sc>v</jats:sc> is quite strong with a small <jats:italic>b</jats:italic>-value, indicating N <jats:sc>v</jats:sc> arises in a cooler H <jats:sc>ii</jats:sc> region resulting from X-ray Auger ionization by Cyg X-1.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report the preliminary modeling of archival Center for High Angular Resolution Astronomy (CHARA)/Visible spEctroGraph and polArimeter interferometric data of a K-giant star using the PHOENIX atmosphere code. We find that our preparatory model that includes only the chromospheric contribution closely reproduces the observed infrared Ca <jats:sc>ii</jats:sc> triplet line profiles of a test star: the K-giant, <jats:italic>β</jats:italic> Cet. This preliminary work requires the additional modeling of the wind contribution to improve the agreement with observations. We plan to perform a systematic study of K-giants chromospheric emission with multi-wavelength and multi-technique observations and modeling. Our plans include extending the modeling work to include the underlying wind component for a larger set of stars. Stellar Parameters and Images with a Cophased Array, the second-generation instrument at CHARA, will be the ideal instrument to perform such observations and reveal the chromospheric activity of K-giants.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In this research note, we outline the extension of the grid of upper atmosphere models first presented in Kubyshkina et al. The original grid is based on a 1D hydrodynamic model and consists of about 7000 models covering planets of a size ranging from that of Earth to twice that of Neptune at orbits corresponding to equilibrium temperatures between 300 and 2000 K around solar-like (0.4 to 1.3 solar mass) stars. The extended and revised grid of models consists of 10,235 points and covers a planetary mass range of up to 109 Earth masses, which allows one to outline the transition between low- and high-gravity hot planets in in short period orbits. We prepared the interpolation tool allowing one to use the grid to define the mass-loss of a planet that falls into the parameter range of the grid. We provide a comparison of our results to common analytical models.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Engulfment of several bulk earthlike planets makes only a small effect on the stellar opacity for a sunlike star.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the discovery of 2MASS J13173072+4833343, a low-mass stellar companion to the ∼5.5 Gyr old white dwarf SDSS J131730.85+483332.8. This companion was discovered through the Backyard Worlds: Planet 9 citizen science collaboration. We obtained a near-infrared spectrum of the companion and determined a spectral type of M8.5. Using the cooling age of the white dwarf, we determined that the stellar companion has a mass of <jats:inline-formula> <jats:tex-math> <?CDATA ${0.077}_{-0.017}^{+0.005}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>0.077</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.017</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.005</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="rnaasabf49aieqn1.gif" xlink:type="simple" /> </jats:inline-formula> <jats:italic>M</jats:italic> <jats:sub>☉</jats:sub>, or <jats:inline-formula> <jats:tex-math> <?CDATA ${80.2}_{-1.8}^{+0.5}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>80.2</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.8</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.5</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="rnaasabf49aieqn2.gif" xlink:type="simple" /> </jats:inline-formula> <jats:italic>M</jats:italic> <jats:sub>Jup</jats:sub>, near the substellar boundary.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Symplectic integrators are widely used for the study of planetary dynamics and other <jats:italic>N</jats:italic>-body problems. In a study of the outer solar system, we demonstrate that individual symplectic integrations can yield biased errors in the semimajor axes and possibly other orbital elements. The bias is resolved by studying an ensemble of initial conditions of the outer solar system. Such statistical sampling could significantly improve measurement of planetary system properties like their secular frequencies. We also compared the distributions of action-like variables between high and low accuracy integrations; traditional statistical metrics are unable to distinguish the distribution functions.</jats:p>