1998A&A...336..654K

We report on the first systematic study of the mass-loss properties of O-rich irregular variables of type Lb. ¹²CO(J=1-0, 2-1, and 3-2) line observations were carried out using the SEST, the Onsala 20m TELESCOPE, the JCMT and the IRAM 30m ANTENNA. In total 20 stars were detected among the 31 objects observed (all are new detections; in three cases detections are precluded because of strong interference from interstellar CO emission). Hence, the detection rate is very high for this sample selected on the basis of the 60µm flux strength. The majority of the detected objects are weak in CO, and the inferred mass-loss rates are low (≲10^–7M_☉/yr). They have, with only a few exceptions, envelopes with small gas expansion velocities (the mean value is ≃8km/s). We find that their mass-loss properties are very similar to those of bright O-rich semiregular (SRa or SRb) and Mira variables, i.e., at least in this mass-loss rate range the stellar mass-loss properties are not strongly influenced by the pulsational behaviour of the star.