SIO MASER SURVEY OF THE GALACTIC BULGE IRAS SOURCES .2. THE AN-VERTICAL-BAR-B-VERTICAL-BAR-LESS-THAN-5-DEGREES STRIPS

We have surveyed Galactic bulge IRAS sources in the strips between -15 degrees < l < 15 degrees and 4 degrees < \b\ < 5 degrees in the SiO J = 1-0 upsilon = 1 and 2 transitions. The sources were selected from t he IRAS Point Source Catalog based on the IRAS 25/12 mu m flux density ratio, extracting dust-enshrouded objects at a distance of about 8 kp c. The SiO masers were detected in 62 of 93 sources surveyed in these strips. The JHKL photometric data (1.2, 1.6, 2.2, and 3.4 mu m) were a lso obtained for 85 sources. Because distances to the IRAS sources in these strips are not known, we have evaluated the distance based on th e observed luminosity. The probability of the objects being a bulge so urce is calculated assuming that the luminosity function of these infr ared sources is the same as that of previously observed \b\ = 7 degree s-8 degrees sources. The contamination due to foreground sources in th e sample is minimized by excluding sources with the bulge probability less than 50%. The SiO maser properties of the \b\ = 4 degrees-5 degre es sources are found to be very similar to those of \b\ = 7 degrees-8 degrees sources. No systematic difference between bulge and disk sourc es is found for the SiO J = 1-0 upsilon = 2/1 intensity ratio. The ave rage rotation rate of the bulge stellar system for the \b\ = 4 degrees -5 degrees sources is found to be 10.8 (+/-2.6) km s(-1) deg(-1), indi cating no sign of increase of the rotation rate at this strip compared with the rate obtained for the \b\ = 7 degrees-8 degrees sources. On the contrary, the velocity dispersions of stars, 91.0 +/- 9.5 km s(-1) , for the \b\ = 4 degrees-5 degrees sources seems appreciably larger t han the dispersion, 72.5 +/- 8.9 km s(-1) obtained for the \b\ = 7 deg rees-8 degrees sources. A small, systematic velocity shift of the radi al velocities is found between the south and north strip sources. If t his shift is interpreted as due to a tilt of the bulge, the tilt angle of the bulge rotation axis to the Galactic circle would be 8(-31)(+27 ) deg, which is slightly smaller than the value obtained for the \b\ = 7 degrees-8 degrees sources.