1996A&A...311..273K

O-rich Semiregular Variables (SRVs) of types SRa and SRb have been observed in the ¹²CO(J=1-0) and (J=2-1) lines using the SEST, La Silla, Chile, and the 20-m telescope at Onsala, Sweden. In total 22 detections (13 are new ones) and 1 tentative detection can be reported among the 48 stars observed. In 7 cases detections are precluded because of strong interference from interstellar CO emission. The majority of the detected objects, covering both small and longer periods, are weak in CO, i.e. they are low mass-loss rate objects (≤10^–7M_☉/yr), and have, with only a few exceptions, envelopes with small expansion velocities (the mean value is ≃8km/s). However, in this respect their properties are very similar to those of bright O-rich Mira variables, whose pulsational periods are on the average 2-3 times higher. A comparison between stellar and circumstellar properties shows that the gas expansion velocity does not depend on the stellar effective temperature, nor on the period. Likewise, we find no correlation between mass-loss rate and period, but there might be a weak dependence of the former on the stellar effective temperature.