This fact, as far as the oxygen isotopic ratios are concerned, leaves little space for the operation of any extra mixing mechanism during the AGB phase. For most of the stars the 16O / 17O / 18O ratios derived are in good agreement with theoretical predictions confirming that, for AGB stars, are established using the values reached after the first dredge-up (FDU) according to the initial stellar mass. The CNO isotope ratios derived in a homogeneous way, were compared with theoretical predictions for low-mass (1.5–3 M ⊙) AGB stars computed with the FUNS code assuming extra mixing both during the RGB and AGB phases. Synthetic spectra calculated in local thermodynamic equillibrium (LTE) with spherical carbon-rich atmosphere models and updated molecular line lists were used. Oxygen isotopic ratios were derived from spectra in the K-band in a sample of galactic AGB carbon stars of different spectral types and near solar metallicity. We aim to redetermine the oxygen ratios in these stars using new spectral analysis tools and further develop discussions on the carbon and nitrogen isotopic ratios in order to elucidate this problem. Previous determinations of the oxygen isotopic ratios in asymptotic giant branch (AGB) carbon stars were at odds with the existing theoretical predictions. When the different dredge-up events mix the burning material with the envelope, valuable information on the nucleosynthesis and mixing processes can be extracted by measuring these isotope ratios.Īims. The abundance ratios of the main isotopes of carbon, nitrogen and oxygen are modified by the CNO-cycle in the stellar interiors. Física Teórica y del Cosmos, Universidad de Granada, 18071 Granada, SpainĮ-mail: Observatorio Astronómico Calar Alto, 04550 Gergal (Almería), Spainģ INAF, Osservatorio Astronomico di Collurania, 64100 Teramo, ItalyĬontext. Astronomical objects: linking to databasesĬ.Including author names using non-Roman alphabets.Suggested resources for more tips on language editing in the sciences Punctuation and style concerns regarding equations, figures, tables, and footnotes
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