Distance determination of mass losing carbon stars from CO and HCN radio observations

Abstract

A method of distance determination of evolved carbon stars is proposed and applied to six stars for which the terminal velocity of expansion and the angular size are obtained from the CO and HCN radio observations made at the Nobeyama Radio Observatory. The method assumes the radiation driven wind in spherical geometry. Within those small samples, however, two types of mass losing stars that are systematically different in the antenna temperature ratio T _A (CO)/T _A (HCN)≷1, in the velocity ratio ν(CO)/ν(HCN)≶ l, and in the angular size ratio θ(CO)/θ(HCN)≷1 seem to be present, suggesting nonspherical geometry of the outflow.