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Isotopic ratios in the red giant component of the recurrent nova T Coronae Borealis


We report the determination of abundances and isotopic ratios for C, O and Si in the photosphere of the red giant component of the recurrent nova T Coronae Borealis from new 2.284–2.402 µm and 3.985–4.155 µm spectroscopy. Abundances and isotopic ratios in the photosphere may be affected by (i) processes in the red giant interior which are brought to the surface during dredge-up, (ii) contamination of the red giant, either during the common envelope phase of the binary evolution or by material synthesised in recurrent nova eruptions, or a combination of the two. We find that the abundances of C, O and Si are reasonably consistent with the expected composition of a red giant after first dredge-up, as is the 16O/17O ratio. The 28Si/29Si ratio is found to be 8.6 ± 3.0, and that for 28Si/30Si is 21.5 ± 3.0. The 12C/13C ratio (10 ± 2) is somewhat lower than expected for first dredge-up. The 16O/18O ratio (41 ± 3) is highly inconsistent with that expected either from red giant evolution (~ 550) or from contamination of the red giant by the products of a nova thermonuclear runaway. In particular the C and O isotopic ratios taken in combination are a puzzle. We urge confirmation of our results using spectroscopy at high resolution. We also encourage a thorough theoretical study of the effects on the secondary star in a recurrent nova system of contamination by ejecta having anomalous abundances and isotopic ratios.

Acceptance Date Aug 26, 2020
Publication Date Sep 8, 2020
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Publisher Oxford University Press
Pages 4853-4863
Keywords nuclear reactions, nucleosynthesis, abundances — stars: AGB and post-AGB — stars: abundances — stars: individual (T CrB) — novae: cataclysmic variables — infrared: stars
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