SIO MASER SURVEY OF THE GALACTIC BULGE IRAS SOURCES .1. THE AN-VERTICAL-BAR-B-VERTICAL-BAR-LESS-THAN-8-DEGREES STRIPS

We have surveyed Galactic bulge IRAS sources in the strips between -15 degrees < l < 15 degrees and 7 degrees < \b\ < 8 degrees in the SiO J = 1-0 v = 1 and 2 transitions. The sources were selected from the IRA S Point Source Catalogue based on the IRAS 12 and 25 mu m flux densiti es, extracting dust-enshrouded objects at a distance of 8 kpc. SiO mas ers were detected in 53 of the 91 sources surveyed in these strips. Be cause distances to the IRAS sources in these strips have been known fr om the period-luminosity relation and periods of intensity variation a t infrared wavelengths measured by others, the contamination by foregr ound sources in the sample can be checked relatively easily and the un certainty in deriving physical parameters of the bulge is minimized. T he detection rate of SiO masers does not depend much on the infrared c olors in the selected color range (logarithm of the IRAS 25 to 12 mu m flux density ratio between -0.15 and 0.3) and the detection rate incr eases with the 12 mu m flux density of the IRAS sources. It has been f ound that the intrinsic SiO maser intensity depends weakly on the mass -loss rate for the bulge and disk SiO maser sources. No systematic dif ference of the SiO maser properties is found between bulge and disk so urces. The radial velocities in the northern strip are shifted systema tically from those in the southern strip by about 50 km s(-1). If this velocity shift is interpreted as due to a tilt of the bulge rotation axis to the galactic longitude circle, the tilt angle of the rotation of the bulge would be 18 degrees((+18 degrees)(-14 degrees)). The angu lar rotation velocity of the bulge stellar system is 7.3 x 10(8) rad y r(-1) (implying the rotation period of 8.6 x 10(7) yr). A Galactic top view of the distribution and the velocity vectors of the bulge SiO ma sers is given.