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arXiv · 2008.12150

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

Ya. V. Pavlenko·A. Evans·D. P. K. Banerjee·T. R. Geballe·U. Munari·R. D. Gehrz·C. E. Woodward·S. Starrfield
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Abstract

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 $μ$m and 3.985--4.155 $μ$m 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 $^{16}$O/$^{17}$O ratio. The $^{28}$Si/$^{29}$Si ratio is found to be $8.6\pm3.0$, and that for $^{28}$Si/$^{30}$Si is $21.5\pm3.0$. The $^{12}$C/$^{13}$C ratio ($10\pm2$) is somewhat lower than expected for first dredge-up. The $^{16}$O/$^{18}$O ratio ($41\pm3$) is highly inconsistent with that expected either from red giant evolution ($\sim550$) 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.

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Ya. V. Pavlenko, A. Evans, D. P. K. Banerjee, T. R. Geballe, U. Munari, R. D. Gehrz, C. E. Woodward, S. Starrfield. 2020-08-27. Isotopic ratios in the red giant component of the recurrent nova T Coronae Borealis. https://doi.org/10.1093/mnras%2Fstaa2658

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