SIMULTANEOUS OBSERVATIONS OF SiO AND H2O MASERS TOWARD SYMBIOTIC STARS

We present the results of simultaneous observations of SiO upsilon = 1, 2, J = 1-0, (SiO)-Si-29 upsilon = 0, J = 1-0, and H2O 6(16)-5(23) maser lines performed with the KVN Yonsei 21 m radio telescope from 2009 November to 2010 January. We searched for these masers in 47 symbiotic stars and detected maser emission from 21 stars, giving the first time detection from 19 stars. Both SiO and H2O masers were detected from seven stars of which six were D-type symbiotic stars and one was an S-type star, WRAY 15-1470. In the SiO maser emission, the (SiO)-Si-28 upsilon = 1 maser was detected from 10 stars, while the upsilon = 2 maser was detected from 15 stars. In particular, the (SiO)-Si-28 upsilon = 2 maser emission without the upsilon = 1 maser detection was detected from nine stars with a detection rate of 60%, which is much higher than that of isolated Miras/red giants. The (SiO)-Si-29 upsilon = 0 maser emission was also detected from two stars, H 2-38 and BF Cyg, together with the (SiO)-Si-28 upsilon = 2 maser. We conclude that these different observational results between isolated Miras/red giants and symbiotic stars may be related with the presence of hot companions in a symbiotic binary system.