VLBI observations of SiO masers at a wavelength of 7 millimeters in late-type stars

Abstract

Results are reported for VLBI observations (75 km baseline, minimum fringe spacing of 0.02 arcsec) of emission from the v = 1, J = 1 - 0 transition of SiO at 43 GHz in the M supergiant VX Sgr and the Mira variable R Cas. It is found that the strongest features of the SiO maser toward R Cas are slightly resolved and have apparent angular diameters of 0.006 arcsec as well as peak brightness temperatures of about 20 billion K, that all these maser features are clustered within a region 0.02 arcsec in diameter, and that the maser features are probably saturated. For the maser in VX Sgr an apparent angular diameter of 0.007 arcsec is determined, along with a peak brightness temperature of 10 billion K and a cluster size of less than 0.05 arcsec. This maser is also shown to be saturated.