Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Measurements made with the Voyager 1 spacecraft indicate that significant levels of compressive fluctuations exist in the inner heliosheath. Some studies have already been performed with respect to the mirror-mode instability in the downstream region close to the solar wind termination shock, and here we extend the investigation to the whole inner heliosheath. We employ quasilinear theory and results from a global magnetohydrodynamic model of the heliosphere to compute the time evolution of both the temperature anisotropy and the energy density of the corresponding magnetic fluctuations, and we demonstrate their likely presence in the inner heliosheath. Furthermore, we compute the associated, locally generated density fluctuations. The results can serve as inputs for future models of the transport of compressible turbulence in the inner heliosheath.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Radioactive isotopes produced in core-collapse supernovae (CCSNe) provide useful insights into the underlying processes driving the collapse mechanism and the origins of elemental abundances. Their study generates a confluence of major physics research, including experimental measurements of nuclear reaction rates, astrophysical modeling, and <jats:italic>γ</jats:italic>-ray observations. Here we identify the key nuclear reaction rates to the nucleosynthesis of observable radioactive isotopes in explosive silicon burning during CCSNe. Using the nuclear reaction network calculator SkyNet and current REACLIB reaction rates, we evolve temperature–density–time profiles of the innermost 0.45 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> ejecta from the core collapse and explosion of a 12 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> star. Individually varying 3403 reaction rates by factors of 100, we identify 141 reactions that cause significant differences in the isotopes of interest, namely, <jats:sup>43</jats:sup>K, <jats:sup>47</jats:sup>Ca, <jats:sup>44,47</jats:sup>Sc, <jats:sup>44</jats:sup>Ti, <jats:sup>48,51</jats:sup>Cr, <jats:sup>48,49</jats:sup>V, <jats:sup>52,53</jats:sup>Mn, <jats:sup>55,59</jats:sup>Fe, <jats:sup>56,57</jats:sup>Co, and <jats:sup>56,57,59</jats:sup>Ni. For each of these reactions, we present a novel method to extract the temperature range pertinent to the nucleosynthesis of the relevant isotope; the resulting temperatures lie within the range <jats:italic>T</jats:italic> = 0.47–6.15 GK. Limiting the variations to within 1<jats:italic>σ</jats:italic> of STARLIB reaction rate uncertainties further reduces the identified reactions to 48 key rates, which can be used to guide future experimental research. Complete results are presented in tabular form.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The atmospheric circulation of tidally locked planets is dominated by a superrotating eastward equatorial jet. We develop a predictive theory for the formation of this jet, proposing a mechanism in which the three-dimensional stationary waves induced by the day–night forcing gradient produce an equatorial acceleration. This is balanced in equilibrium by an interaction between the resulting jet and the vertical motion of the atmosphere. The three-dimensional structure of the zonal acceleration is vital to this mechanism. We demonstrate this mechanism in a hierarchy of models. We calculate the three-dimensional stationary waves induced by the forcing on these planets and show the vertical structure of the zonal acceleration produced by these waves, which we use to suggest a mechanism for how the jet forms. General circulation model simulations are used to confirm the equilibrium state predicted by this mechanism, where the acceleration from these waves is balanced by an interaction between the zonal-mean vertical velocity and the jet. We derive a simple model of this using the “Weak Temperature Gradient” approximation, which gives an estimate of the jet speed on a terrestrial tidally locked planet. We conclude that the proposed mechanism is a good description of the formation of an equatorial jet on a terrestrial tidally locked planet and should be useful for interpreting observations and simulations of these planets. The mechanism requires assumptions such as a large equatorial Rossby radius and weak acceleration due to transient waves, and a different mechanism may produce the equatorial jets on gaseous tidally locked planets.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Solar-type young stellar objects undergo periodic, energetic outbursts that appear to be the result of enhanced mass accretion driven by the gravitational instability of their disks. Such FU Orionis outbursts may have profound consequences for the earliest solids in a protoplanetary disk, namely the refractory inclusions containing abundant calcium and aluminum (CAIs). We present models of the orbital evolution of centimeter-radius particles representing large CAIs in marginally gravitationally unstable disks. The hydrodynamical evolution of the disks is calculated with a fully three-dimensional code, including compressional heating and cooling in the beta cooling approximation. The particles are initially distributed uniformly throughout the disk, which extends from 1 to 10 au around a solar-mass protostar, but within ∼100 yr the particles are concentrated by gas drag into regions surrounding the spiral arms and rings formed by the gas disk. The particles settle down toward the disk midplane, only to be lofted repeatedly upward by shock fronts. Large-scale radial transport both outward and inward occurs, with significant numbers of particles reaching the outer disk (∼10 au) and surviving for considerably longer times than would be the case in a quiescent disk with gas pressure monotonically decreasing with distance from the protostar. Individual particles experience wide ranges of disk temperatures during their journeys, ranging from 60 K in the outer disk to nearly 2000 K in spiral features. Future work will consider the implications for CAI rims of the thermochemical processing experienced during FU Orionis outbursts.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>When galaxies merge, the supermassive black holes in their centers may form binaries and emit low-frequency gravitational radiation in the process. In this paper, we consider the galaxy 3C 66B, which was used as the target of the first multimessenger search for gravitational waves. Due to the observed periodicities present in the photometric and astrometric data of the source, it has been theorized to contain a supermassive black hole binary. Its apparent 1.05-year orbital period would place the gravitational-wave emission directly in the pulsar timing band. Since the first pulsar timing array study of 3C 66B, revised models of the source have been published, and timing array sensitivities and techniques have improved dramatically. With these advances, we further constrain the chirp mass of the potential supermassive black hole binary in 3C 66B to less than (1.65 ± 0.02) × 10<jats:sup>9</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> using data from the NANOGrav 11-year data set. This upper limit provides a factor of 1.6 improvement over previous limits and a factor of 4.3 over the first search done. Nevertheless, the most recent orbital model for the source is still consistent with our limit from pulsar timing array data. In addition, we are able to quantify the improvement made by the inclusion of source properties gleaned from electromagnetic data over “blind” pulsar timing array searches. With these methods, it is apparent that it is not necessary to obtain exact a priori knowledge of the period of a binary to gain meaningful astrophysical inferences.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Through the use of the high-resolution spectral data and the broadband imaging obtained with the Goode Solar Telescope at the Big Bear Solar Observatory on 2013 June 6, the spectra of three typical photospheric bright points (PBPs) have been analyzed. Based on the H<jats:italic>α</jats:italic> and Ca <jats:sc>ii</jats:sc> 8542 Å line profiles, as well as the TiO continuum emission, for the first time, the non-LTE semiempirical atmospheric models for the PBPs are computed. The attractive characteristic is the temperature enhancement in the lower photosphere. The temperature enhancement is about 200–500 K at the same column mass density as in the atmospheric model of the quiet-Sun. The total excess radiative energy of a typical PBP is estimated to be 1 × 10<jats:sup>27</jats:sup>–2 × 10<jats:sup>27</jats:sup> erg, which can be regarded as the lower limit energy of the PBPs. The radiation flux in the visible continuum for the PBPs is about 5.5 × 10<jats:sup>10</jats:sup> erg cm<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup>. Our result also indicates that the temperature in the atmosphere above PBPs is close to that of a plage. It gives clear evidence that PBPs may contribute significantly to the heating of the plage atmosphere. Using our semiempirical atmospheric models, we estimate self-consistently the average magnetic flux density <jats:italic>B</jats:italic> in the PBPs. It is shown that the maximum value is about 1 kG, and it decreases toward both higher and lower layers, reminding us of the structure of a flux tube between photospheric granules.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Recent surveys uncovered new young massive clusters (YMCs) that host dozens of red supergiants (RSGs) in the inner Milky Way. These clusters are ideal for studying the most recent and violent star formation events in the inner Galaxy. However, due to the high extinction that affects the Galactic plane, they need to be studied through infrared (IR) spectroscopy. IR spectra of RSGs have proven to be powerful tools for obtaining chemical abundances. We present the first [Fe/H] measurement (−0.07 ± 0.02) for the YMC VdBH 222 through analysis of its RSGs using Very Large Telescope/X-shooter spectra. We find no evidence for multiple stellar populations in this YMC, contrary to what is routinely observed in older massive clusters.</jats:p>