Mass Loss from Evolved Stars and Submillimeter Observations

Abstract

When low and intermediate mass stars evolve off the main sequence, they become red giants. During the first ascent up the red giant branch, the stars lose mass at a modest rate ~10⁻⁹ M₀ yr⁻¹, Dupree 1986). However, during the second ascent up the red giant branch, the asymptotic giant branch (AGB), stars lose mass at a much greater rate; up to 10⁻⁴ Mo yr⁻¹ (Zuckerman 1980, Jura 1986a, Olofsson 1985). Dust grains typically form in these outflows from cool giants and the circumstellar dust absorbs optical light from the photosphere and re-radiates this energy in the infrared and submillimeter. Consequently, asymptotic giant branch stars can be very powerful sources of infrared radiation and many of the brightest 10 µm sources in the sky are evolved stars (Kleinmann, Gillett and Joyce 1981). In fact, in some galaxies, the total emission at 12 µm might even be dominated by these stars (Jura et al. 1987, Soifer et al. 1986, Impey, Wynn-Williams and Becklin 1986). These stars are also powerful sources of submillimeter radiation (Sopka et al. 1985) and they are the major topic of this paper.