Turbulence, Convection, and Mixing in Red Giant Stars: Some Empirical Approaches Based on High Resolution Spectroscopy
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.
KeywordsRadial Velocity Equivalent Width Asymptotic Giant Branch Carbon Star Cool Star
Unable to display preview. Download preview PDF.
- Connes, P. and Michel, G.: 1974, Astrophys. J. 190 L29.Google Scholar
- Hall, D. N. B., Ridgway, S. T., Bell, E. A., and Yarborough, J. M.: 1979, Proc. Soc. Photo-Opt. Instrum. Eng. 172, 121.Google Scholar
- Nordlund, A.: 1980, in D. F. Gray and J. L. Linsky (eds.), ‘Stellar Turbulence’, IAU Colloq. 51, 213.Google Scholar
- Osawa, K.: 1965, Astron. Herald 58, 28 (in Japanese).Google Scholar
- Pierce, A. K. and Breckinridge, J. B.: 1973, Kitt Peak National Observatory Contr., No. 559.Google Scholar
- Ridgway, S. T. and Friel, E. D.: 1981, in C. Chiosi and R. Stalio (eds.),Effects of Mass Loss on Stellar Evolution, D. Reidel, Publ. Co., Dordrecht, Holland, p. 119.Google Scholar
- Smith, M. A.: Astrophys. J. 242 LI 15.Google Scholar
- Tsuji, T.: 1979, New Zealand J. Sci. 22, 415, ( Proc. First Asian-South Pacific Regional Meeting of IAU ).Google Scholar
- Tsuji, T.: 1985, in M. Jaschek and P. C. Keenan (eds.), Cool Stars with Excesses of Heavy Elements, D. Reidel, Publ. Co., Dordrecht, Holland, p. 295.Google Scholar