C, N, O, and Their Isotope Abundances in Coolest Stars of the Red Giant Branch

Abstract

A quantitative analysis based on model atmospheres is applied to high resolution IR spectrum of α Herculis(M5Ib-II) observed by P.Connes with his Fourier Transform Spectrometer. Analysis on CO, OH, and CN(first detected in such a cool oxygen-rich giant) gives: (1)[C/H]= -0.7±0.3,[N/H] =+0.8±0.4,[O/H]=-0.2±0.4, where[M/H]=log(M/H)_*-log(M/H)_⊙, and (C+N+O)/H is solar within 15%. (2) ¹²/ C=¹³ ±5. (3) ¹⁶0/¹⁷0=180± 80. This shows that the products of CNO tri-cycles are mixed to the surface, but actual process of the mixing is still to be identified. For this purpose, similar analysis is being extended to a larger sample of red giant stars.