Astron. Astrophys. 319, 607-616 (1997)

6. Conclusions

We have observed a sample of 37 O-rich stars (30 Miras and semiregular variables, and 7 OH-IR objects) with the 30-m IRAM radiotelescope in the lines of SiO v =1 J =2 1 and ¹² CO J =2 1. Broad SiO wings have been detected in 52% of the Mira and semiregular stars. Most of these wings appear in the red part of the line reaching and even exceeding the corresponding CO velocities. A few objects show broad wings in the blue and in the red.

The standard models for the kinematics of the gas in the acceleration region of the circumstellar envelope fail to explain the observations. Pulsation of the gas associated to the star activity, rotation, and asymmetric mass loss processes are the most plausible processes involved in the formation of SiO line wings. Unfortunately, our limited angular resolution precludes a definitive answer to the origin of these wings.

A monitoring of the observed stars seems necessary to follow the variation of the SiO maser line wings as a function of the stellar phase. Such a monitoring has been started with the 30-m IRAM telescope and the results will be published elsewhere.

Sensitive VLBI, VLBA or VLA observations are needed to find the exact spatial extent and position of the blue and red wings observed in the maser emission of SiO in O-rich evolved stars.

© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998
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