Turbulence, Convection, and Mixing in Red Giant Stars: Some Empirical Approaches Based on High Resolution Spectroscopy

Abstract

The differential velocity field in cool stars can be measured effectively on photographic plates by the use of a PDS micro-densitometer, from which it is shown that radial velocity gradients are larger for stars with larger turbulent velocities, which are determined from the high resolution echellograms. This indicates that the stellar turbulence may have something to do with the differential velocity field in stellar atmospheres. As an observational probe of the mixing processes in red giant stars, stellar abundances that are sensitive to mixing are determined on the basis of high resolution Fourier Transform spectroscopy. For example, the ¹²C/¹³C ratio has now been determined for large number of red giant stars and shows characteristic changes through the first red giant branch to the asymptotic giant branch, including both the pre-thermal pulsing and the thermal pulsing phases. This information, together with additional information on the ¹⁶O/¹⁷O ratio and on CNO abundances, provides useful constraints on the theory of mixing in red giant stars.

Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.