A study of circumstellar envelopes around bright carbon stars. I - Structure, kinematics, and mass-loss rate.

Results are presented of a survey of circumstellar CO emission on a sample of bright carbon stars, which is relatively complete out to about 900 pc from the sun. A total of 68 detections were made. All objects within 600 pc of the sun were detected. It is suggested that the large majority of all carbon stars have circumstellar envelopes. The CO-emitting parts of these envelopes have angular sizes less than about 15 arcsec. The median gas expansion velocity is 12.5 km/s, and the expansion velocities for the majority of the objects fall in the range 9-15 km/s. The median mass-loss rate is 1.5 x 10 exp -7 solar mass/yr, and the mass loss rate for the majority of stars lies within the narrow range (0.8-2.5) x 10 exp -7 solar mass/yr. Circumstellar and photospheric HCN, CN, and CS abundances are estimated and compared for a sample for bright carbon stars. The chemistry in the envelope around R Scl is determined.