Rotating Models of Low Mass Giants: Rotational Evolution and Surface Abundance Anomalies

Abstract

We present some first results of stellar models of low mass, solar metallicity giants that include rotation and the mixing associated with it. We base our choice of initial conditions and input physics on observational constraints obtained for main sequence (MS) and horizontal branch (HB) stars, and obtain what can be regarded as a “best case scenario” for rotational mixing. These observations suggest local conservation of angular momentum in the cores and constant specific angular momentum in convective regions on the red giant branch (RGB). We show that under these circumstances and with moderate rotation rates at the turnoff it is possible to obtain enough mixing in order to reproduce the anomalous abundance ratios of the CNO species seen in giants. It is also shown that solid body rotation in the convective envelope fails to account for the observations. It is found that rotational mixing is inefficient on the lower RGB, so there is no need to invoke any inhibiting role of μ–gradients.