SiO maser survey of the large-amplitude variables in the galactic center

Abstract

We have surveyed ∼ 400 known large-amplitude variables within 15′ of the galactic center in the SiO J = 1-0 v = 1 and 2 maser lines at 43 GHz, resulting in 180 detections. SiO lines were detected from 16 other sources located within 20″ of the program objects. The detection rate of 48% is comparable to that in bulge IRAS surveys. Among the detections, five stars have radial velocities greater than 200kms -1. The detection rate increases steeply with the period of light variation, particularly for stars with P > 500 d, where it exceeds 80%. At a given period, the SiO detection rate is approximately three-times that for OH. These facts suggest that the large-amplitude variables in the Nuclear Disk region are AGB stars similar in their overall properties to the inner and outer bulge IRAS/SiO sources. From the set of radial velocity data, the mass distribution within 30 pc of the galactic center was derived based on the collisionless Boltzmann equation integrated along the line of sight. The mass is about 6.5 (±0.7) × 10 7M ⊙ and the mass of the central black hole is 2.7 (±1.3) × 10 6M ⊙. From the line-of-sight velocity of each star and its potential energy we conclude that the five high-velocity stars come from galactocentric distances as far as 300 pc. A high-velocity subsample of stars with negative radial velocities exhibits a tendency to have brighter K magnitudes than a subsample with positive velocities. The origin of these stars is discussed.