Evolution and Problems of Red Long Period Variables

Abstract

Variability on the red giant branch (RGB) occurs at an interesting and important stage in the life of a star. This phase of evolution is characterized by a substantial amount of mass loss (as a continuous stellar wind or as an abrupt planetary nebula ejection), by flashing of the helium burning shell (at least in stars less massive than ~ 8 M) and by surface enrichment of elements heavier than hydrogen. The galactic importance of these processes is illustrated by the calculations of Cahn and Wyatt (1978) who estimate that material is presently being lost by stars on the RGB at a rate which is roughly equal to the rate at which material is being locked up in stars by star formation. A complementary calculation by Iben and Truran (1978) shows that shell flashing in red giant stars, coupled with mass loss, is a major source of enrichment of the interstellar medium over a wide range of atomic mass from C to heavy s-process elements. Hopefully, studies of the red long period variable (RLPV) stars can assist in the investigation of some of the above processes so that a comprehensive picture of the later phases of stellar evolution can be obtained.