Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Helioseismic observations have revealed many properties of the Sun: the depth and helium abundance of the convection zone, the sound speed, and the density profiles in the solar interior. Those constraints have been used to judge the stellar evolution theory. With the old solar composition (e.g., GS98), the solar standard model is in reasonable agreement with the helioseismic constraints. However, a solar model with a revised composition (e.g., AGSS09) with a low abundance <jats:italic>Z</jats:italic> of heavy elements cannot be consistent with those constraints. This is the so-called “solar abundance problem,” standing for more than 10 yr even with the recent upward revised Ne abundance. Many mechanisms have been proposed to mitigate the problem. However, there is still no low-<jats:italic>Z</jats:italic> solar model satisfying all helioseismic constraints. In this paper, we report a possible solution to the solar abundance problem. With some extra physical processes that are not included in the standard model, solar models can be significantly improved. Our new solar models with convective overshoot, the solar wind, and early mass accretion show consistency with helioseismic constraints, the solar Li abundance, and observations of solar neutrino fluxes.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a detailed spectroscopic analysis of RR Lyrae (RRL) variables in the globular cluster NGC 5139 (<jats:italic>ω</jats:italic> Cen). We collected optical (4580–5330 Å), high-resolution (<jats:italic>R</jats:italic> ∼ 34,000), high signal-to-noise ratio (∼200) spectra for 113 RRLs with the multifiber spectrograph M2FS at the <jats:italic>Magellan</jats:italic>/Clay Telescope at Las Campanas Observatory. We also analyzed high-resolution (<jats:italic>R</jats:italic> ∼ 26,000) spectra for 122 RRLs collected with FLAMES/GIRAFFE at the Very Large Telescope, available in the ESO archive. The current sample doubles the literature abundances of cluster and field RRLs in the Milky Way based on high-resolution spectra. Equivalent-width measurements were used to estimate atmospheric parameters, iron, and abundance ratios for <jats:italic>α</jats:italic> (Mg, Ca, Ti), iron peak (Sc, Cr, Ni, Zn), and s-process (Y) elements. We confirm that <jats:italic>ω</jats:italic> Cen is a complex cluster, characterized by a large spread in the iron content: −2.58 ≤  [Fe/H] ≤  −0.85. We estimated the average cluster abundance as <jats:inline-formula> <jats:tex-math> <?CDATA $\langle [\mathrm{Fe}/{\rm{H}}]\rangle =-1.80\pm 0.03$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab2e76ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, with <jats:italic>σ</jats:italic> = 0.33 dex. Our findings also suggest that two different RRL populations coexist in the cluster. The former is more metal-poor ([Fe/H] ≲ − 1.5), with almost solar abundance of Y. The latter is less numerous, more metal-rich, and yttrium enhanced ([Y/Fe] ≳ 0.4). This peculiar bimodal enrichment only shows up in the s-process element, and it is not observed among lighter elements, whose [X/Fe] ratios are typical for Galactic globular clusters.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the first joint observation of a small microflare in X-rays with the <jats:italic>Nuclear Spectroscopic Telescope ARray</jats:italic> (<jats:italic>NuSTAR</jats:italic>), in UV with the <jats:italic>Interface Region Imaging Spectrograph</jats:italic> (<jats:italic>IRIS</jats:italic>), and in EUV with the <jats:italic>Solar Dynamics Observatory</jats:italic>/Atmospheric Imaging Assembly (<jats:italic>SDO</jats:italic>/AIA). These combined observations allow us to study the hot coronal and cooler chromospheric/transition region emission from the microflare. This small microflare peaks from 2016 July 26 23:35 to 23:36 UT, in both <jats:italic>NuSTAR</jats:italic>, <jats:italic>SDO</jats:italic>/AIA, and <jats:italic>IRIS</jats:italic>. Spatially, this corresponds to a small loop visible in the <jats:italic>SDO</jats:italic>/AIA Fe <jats:sc>xviii</jats:sc> emission, which matches a similar structure lower in the solar atmosphere seen by <jats:italic>IRIS</jats:italic> in SJI1330 and 1400 Å. The <jats:italic>NuSTAR</jats:italic> emission in both 2.5–4 and 4–6 keV is located in a source at this loop location. The <jats:italic>IRIS</jats:italic> slit was over the microflaring loop, and fits show little change in Mg <jats:sc>ii</jats:sc> but do show intensity increases, slight width enhancements, and redshifts in Si <jats:sc>iv</jats:sc> and O <jats:sc>iv</jats:sc>, indicating that this microflare had most significance in and above the upper chromosphere. The <jats:italic>NuSTAR</jats:italic> microflare spectrum is well fitted by a thermal component of 5.1 MK and 6.2 × 10<jats:sup>44</jats:sup> cm<jats:sup>−3</jats:sup>, which corresponds to a thermal energy of 1.5 × 10<jats:sup>26</jats:sup> erg, making it considerably smaller than previously studied active region microflares. No non-thermal emission was detected but this could be due to the limited effective exposure time of the observation. This observation shows that even ordinary features seen in UV can remarkably have a higher-energy component that is clear in X-rays.</jats:p>