ABSOLUTE POSITIONS OF SIO MASERS

The Hat Creek millimeter array was used to measure the absolute radio positions of the v = 1, J = 2 - 1 (v = 86 GHz) SiO masers toward nine stars, including the infrared source IRc2 in Orion. Typical position uncertainties are ± 0.15 arcsec. Optical positions accurate to ± 0.05″ are available for seven of the stars. For six of these - O Cet, R Leo, W Hya, Χ Cyg, R Aqr, and R Cas - the stellar and maser positions differ by less than 0.35″. The exception is VY CMa, for which the optical position is displaced by 1.1″ from the maser. The optical position of the eighth star, VX Sgr, is less accurately known, but is marginally consistent with the maser position. The SiO maser toward Orion-IRc2 is coincident, within the uncertainties, with a radio-continuum source observed at the VLA.