SiO maser emission in evolved stars : relation to IR continuum.

The authors present observations of SiO masers at 43 GHz (υ = 1, 2; J = 1-0), made with the Yebes radiotelescope. They report the detection of 11 new SiO stars and the confirmation of 1 previous tentative detection, in a total of 64 observed objects. The analysis of the SiO and middle IR measurements yields a very good correlation between maser intensity and 8 μm continuum for oxygen-rich Mira variables and late-type supergiants. This correlation argues in favour of the radiative pump of the maser, against collisional models, and is also useful in the characterization of the SiO maser emitters: the comparison of the respective regions occupied by these groups of objects in the SiO-IR diagram shows that the emission of the C stars is ⪆100 times weaker than that of the oxygen-rich objects, and that the S stars seem to be an intermediate case, being placed between the C and M distributions.