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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It is well known that fullerenes – big, complex, and highly resistant carbon molecules with potential applications in nanotechnology – are mostly seen in planetary nebulae (PNe); old dying stars with progenitor masses similar to our Sun. Fullerenes, like C60 and C70, have been detected in PNe whose infrared (IR) spectra are dominated by broad unidentified IR (UIR) plateau emissions. The identification of the chemical species (structure and composition) responsible for such UIR emission widely present in the Universe is a mystery in astrochemistry; although they are believed to be carbon-rich
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Stellar ages are key to several fields of astrophysics such as exoplanet research, galactic-archeology, and of course stellar physics. Obtaining the ages of stars is however not straightforward and requires stellar modeling. The most widely used technique only requires stellar colors or temperature and surface gravity, but the uncertainties are quite large. This technique is most efficient for stars belonging to clusters, as they were born from the same molecular cloud and share the same ages. In the last decades, based on the study of stellar acoustic waves, asteroseismology became the most
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