The carbon Cepheid RT Trianguli Australis:: additional evidence of triple-α and CNO cycling

We have used echelle spectra of resolving power 35 000 to derive chemical abundances and the C-12/C-13 ratio in the 1.9-d carbon Cepheid RT TrA and the Cepheid U TrA, employed as a comparison star. We confirm that RT TrA is very metal-rich with [Fe/H ] = +0.4. In addition, C and N are substantially in excess, and a small deficiency in O is present. We interpret these anomalies as resulting from the appearance on the stellar surface of material enriched in C-12 by the 3-alpha process, followed by CNO cycling to convert C-12 to C-13 and N-14. In addition, some O-16 has been processed to N-14. The partial processing of O-16 to N-14 indicates that substantial O-17 may be present. Proton capture seems to have enhanced Na-23 from the Ne isotopes.