Mass loss from evolved stars. I - Observations of 17 stars in the CO/2-1/ line

Abstract

Observations of 29 evolved stars in the CO J = 2-1 line are reported. For 17 of the stars, CO emission from circumstellar molecular gas is detected. Four of the stars (R Leo, R LMi, RX Boo, and Alpha Ori) are detected as CO sources for the first time. The data are analyzed using a simple approximate model of the molecular emission from a stellar molecular envelope, and values of the mass-loss rate are found. Most of the stellar envelopes are found to be optically thick in the CO lines. The mass loss rates for the carbon stars are seen as too large in many cases to be driven by radiation pressure on dust in the envelope. For the Mira variables and possibly for the S stars, the fraction of the stellar photon momentum corresponding to the observed mass loss rate is found to correlate with the amount of dust in the envelope.