Recently, Delgado-Inglada and collaborators have shown that low-mass (between one and three times the mass of the Sun) planetary nebulae are rich in oxygen, but the standard theoretical models do not predict this. In this work we explain this phenomenon for the first time using theoretical models of nucleosynthesis (production of chemical elements in the interiors of stars) in their precursor AGB stars, which include convective processes, (which transport chemical elements created in the interior to the surface of the star) more efficient than in the standard models. This discovery calls into question the traditional role of planetary nebulae as indicators of metallicity, which is the term used to cover the abundance of the elements which are heavier than hydrogen and helium initially present in the Universe, because now it has been confirmed theoretically that they are intrinsically rich in oxygen. The abundance of oxygen has been used historically to study the differences in the metallicity of our Galaxy and those of other nearby galaxies. In its place, this work confirms that other elements which are not so affected by stellar evolution, such as argon or chlorine should be used as indicators of metallicity. In the future, it will be necessary to use the predictions of these new models to analyse in detail the effect of these oxygen producing stars on the models of chemical evolution of galaxies; in fact they may have an important effect on the characteristic time scales for the formation of the majority of the stars in galaxies.
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H II regions are ionized nebulae associated with the formation of massive stars. They exhibit a wealth of emission lines in their spectra that form the basis for estimation of chemical composition. The amount of heavy chemical elements is essential to the understanding of important phenomena such as nucleosynthesis, star formation and chemical evolution of galaxies. For over 80 years, however, a discrepancy exists of a factor of around two between heavy-element abundances (the so-called metallicity) derived from the two main kinds of emission lines that can be measured in nebular spectra
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CaII Kgrains, i.e., intermittent, short-lived (about 1 minute), periodic (2-4 minutes), pointlike chromospheric brightenings, are considered to be the manifestations of acoustic waves propagating upward from the solar surface and developing into shocks in the chromosphere. After the simulations of Carlsson and Stein, we know that hot shocked gas moving upward interacting with the downflowing chromospheric gas (falling down after having been displaced upward by a previous shock) nicely reproduces the spectral features of the CaII K profiles observed in such grains, i.e., a narrowband emission
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The cosmic evolution of the barred galaxy population provides key information about the secular evolution of galaxies and the settling of rotationally dominated discs. We study the bar fraction in the SMACSJ0723.37323 (SMACS0723) cluster of galaxies at z = 0.39 using the Early Release Observations obtained with the NIRCam instrument mounted on the JWST telescope. We visually inspected all cluster member galaxies using the images from the NIRCam F200W filter. We classified the galaxies into ellipticals and discs and determine the presence of a bar. The cluster member selection was based on a
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