Carbon-rich RR Lyr type stars
George Wallerstein, V. V. Kovtyukh, and S. M. Andrievsky
TL;DR
This study measures CNO element abundances in 12 RR Lyrae stars, revealing some with carbon enhancement likely caused by helium flash processes, offering insights into stellar evolution.
Contribution
It provides new CNO abundance measurements in RR Lyrae stars and proposes a novel explanation for carbon enhancement related to helium flash events.
Findings
Some RR Lyrae stars show significant carbon enhancement.
Carbon enhancement is linked to helium flash and convective mixing.
Red giant progenitors typically show carbon deficiency.
Abstract
We have derived CNO abundances in 12 RR Lyrae stars. Four stars show [C/Fe] near 0.0 and two stars show [C/Fe] = 0.52 and 0.65. Red giant branch stars, which are known to be the predecessors of RR Lyrae stars, generally show a deficiency of carbon due to proton captures during their evolution from the main sequence up the giant branch. We suggest that the enhancement of carbon is due to production during the helium flash combined with mixing to the surface by vigorous convection induced by the flash itself.
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