Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Spectral observations of the type-IIb supernova (SN) 2016gkg at 300–800 days are reported. The spectra show nebular characteristics, revealing emission from the progenitor star’s metal-rich core and providing clues to the kinematics and physical conditions of the explosion. The nebular spectra are dominated by emission lines of [O <jats:sc>i</jats:sc>] <jats:italic>λλ</jats:italic>6300, 6364 and [Ca <jats:sc>ii</jats:sc>] <jats:italic>λλ</jats:italic>7292, 7324. Other notable, albeit weaker, emission lines include Mg I] <jats:italic>λ</jats:italic>4571, [Fe <jats:sc>ii</jats:sc>] <jats:italic>λ</jats:italic>7155, O I <jats:italic>λ</jats:italic>7774, Ca II triplet, and a broad, boxy feature at the location of H<jats:italic>α</jats:italic>. Unlike in other stripped-envelope SNe, the [O <jats:sc>i</jats:sc>] doublet is clearly resolved due to the presence of strong narrow components. The doublet shows an unprecedented emission line profile consisting of at least three components for each [O <jats:sc>i</jats:sc>]<jats:italic>λ</jats:italic>6300, 6364 line: a broad component (width ∼2000 km s<jats:sup>−1</jats:sup>), and a pair of narrow blue and red components (width ∼300 km s<jats:sup>−1</jats:sup>) mirrored against the rest velocity. The narrow component appears also in other lines, and is conspicuous in [O <jats:sc>i</jats:sc>]. This indicates the presence of multiple distinct kinematic components of material at low and high velocities. The low-velocity components are likely to be produced by a dense, slow-moving emitting region near the center, while the broad components are emitted over a larger volume. These observations suggest an asymmetric explosion, supporting the idea of two-component ejecta that influence the resulting late-time spectra and light curves. SN 2016gkg thus presents striking evidence for significant asymmetry in a standard-energy SN explosion. The presence of material at low velocity, which is not predicted in 1D simulations, emphasizes the importance of multidimensional explosion modeling of SNe.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the results of high spatial resolution HCO<jats:sup>+</jats:sup>(1−0) and HCN(1−0) observations of the N55 south region (N55-S) in the Large Magellanic Cloud (LMC), obtained with the Atacama Large Millimeter/submillimeter Array (ALMA). N55-S is a relatively less extreme star-forming region of the LMC characterized by a low radiation field. We carried out a detailed analysis of the molecular emission to investigate the relation between dense molecular clumps and star formation in the quiescent environment of N55-S. We detect 10 molecular clumps with significant HCO<jats:sup>+</jats:sup>(1−0) emission and 8 with significant HCN(1−0) emission, and estimate the molecular clump masses by virial and local thermodynamic equilibrium analysis. All identified young stellar objects (YSOs) in N55-S are found to be near the HCO<jats:sup>+</jats:sup> and HCN emission peaks showing the association of these clumps with recent star formation. The molecular clumps that have associated YSOs show relatively larger line widths and masses than those without YSOs. We compare the clump properties of N55-S with those of other giant molecular clouds (GMCs) in the LMC and find that N55-S clumps possess similar size but relatively lower line width and larger HCN/HCO<jats:sup>+</jats:sup>(1−0) flux ratio. These results can be attributed to the low radiation field in N55-S resulted by relatively low star formation activity compared to other active star-forming regions like 30 Doradus-10 and N159. The dense gas fraction of N55-S is ∼0.025, lower compared to other GMCs of the LMC supporting the low star formation efficiency of this region.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The tearing mode instability is one important mechanism that may explain the triggering of fast magnetic reconnection in astrophysical plasmas, such as the solar corona and the Earth's magnetosphere. In this paper, the linear stability analysis of the tearing mode is carried out for a current sheet in the presence of a guide field, including the Hall effect. We show that the presence of a strong guide field does not modify the most unstable mode in the 2D wavevector space orthogonal to the current gradient direction, which remains the fastest-growing parallel mode. With the Hall effect, the inclusion of a guide field turns the nondispersive propagation along the guide field direction to a dispersive one. The oblique modes have a wavelike structure along the normal direction of the current sheet and a strong guide field suppresses this structure while making the eigenfunctions asymmetric.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Turbulent mixing in the radiative regions of stars is usually either ignored or crudely accounted for in most stellar evolution models. However, there is growing evidence that such mixing is present and can affect various aspects of a star’s life. Here, we present a first attempt at quantifying mixing by horizontal shear instabilities in stars using direct numerical simulations. The shear is driven by a body force, and rapidly becomes unstable. At saturation, we find that several distinct dynamical regimes exist, depending on the relative importance of stratification and thermal diffusion. In each of the regimes identified, we propose a certain number of theoretically motivated scaling laws for the turbulent vertical eddy scale, the turbulent diffusion coefficient, and the amplitude of temperature fluctuations (among other quantities). Based on our findings, we predict that the majority of stars should fall into one of two categories: high Péclet number stratified turbulence, and low Péclet number stratified turbulence. The latter is presented in a related paper by Cope et al., while the former is discussed here. Applying our results to the solar tachocline, we find that it should lie in the high Péclet number stratified turbulence regime, and predict a substantial amount of vertical mixing for temperature, momentum, and composition. Taken as is, the new turbulence model predictions are incompatible with the Spiegel &amp; Zahn model of the solar tachocline. However, rotation and magnetic fields are likely to affect the turbulence, and need to be taken into account in future studies.</jats:p>