SiO masers in stars in the inner and outer galactic disk

Observations in the J = 1-0, v = 1 and v = 2 (SiO)-Si-28 and v = 0 (SiO)-Si -29 maser lines were made towards 97 outer- and 19 inner-disk IRAS sources with typical IRAS colors of AGE stars. 21 new (SiO)-Si-28 and 1 new (SiO)-S i-29 maser sources were detected above the 5 sigma level of similar to 1 Jy with the Nobeyama 45 m telescope. Collecting all of the observational data in SiO J = 1-0 maser lines taken with a 45 m telescope, a comparison is ma de between the outer-disk, inner-disk, and bulge samples. The samples, them selves, align a sequence of mid-infrared color, flux at 12 mu m and IRAS va riability index. The detection rates are 66%, 51%, and 31%, respectively, i n the bulge, inner disk, and outer disk. This fact is consistent with the t endency of increasing proportion of C-rich stars in the IRAS sample and met allicity gradient with the galactocentric distance.