SiO Maser Survey of the Large-Amplitude Variables in the Galactic Center

We have surveyed ~400 known large-amplitude variables within 15' of thegalactic center in the SiO J=1--0 v=1 and 2 maser lines at 43 GHz, resulting in179 detections. SiO lines were also detected from 16 other resulting in 180detections. SiO lines were also detected from 16 other sources, which arelocated within 20" (the telescope half beamwidth) of the program objects. Thedetection rate of 48 percent is comparable to that obtained in Bulge IRASsource surveys. Among the SiO detections, five stars have radial velocitiesgreater than 200 km/s. The SiO detection rate increases steeply with the periodof light variation, particularly for stars with P>500 d, where it exceeds 80%.We found that, at a given period, the SiO detection rate is approximately threetimes that for OH. These facts suggest that the large-amplitude variables inthe Nuclear Disk region are AGB stars similar in their overall properties tothe inner and outer Bulge IRAS/SiO sources. From the set of radial velocitydata, the mass distribution within 30 pc of the galactic center is derived by anew method which is based on the collisionless Boltzmann equation integratedalong the line of sight. The mass within 30 pc is about 6.4 [\pm 0.7] \times10^7 M_{\odot} and the mass of the central black hole is 2.7 [\pm 1.3] \times10^6 M_{\odot}. Consideration of the line-of-sight velocity of each star andits potential energy leads to the conclusion that the five high-velocity starscome from galactocentric distances as high as 300 pc. The high-velocitysubsample of stars with negative radial velocities exhibits a tendency to havebrighter K magnitudes than the subsample of stars with positive velocities. Theorigin of these high-velocity stars is discussed.