SiO maser survey toward the inner galactic disk: 40° ≤ l ≤ 70° and |b| ≤ 10°

Abstract

We present the results of an SiO maser survey for color-selected IRAS sources in the area 40° < l < 70° and |b| < 10° in the SiO J = 1-0, v = 1 and 2 transitions (∼ 43GHz). We detected 134 out of 272 observed sources in SiO masers; 127 were new detections. A systematic difference in the detection rates between SiO and OH maser searches was found. Especially, in the color ranges with log(F25/F12) smaller than -0.1, the detection rate of the SiO masers is significantly higher than that of OH masers. We found a possible kinematic influence of the Galactic arm on the distribution of SiO maser sources. It was found that the velocity dispersion of SiO maser sources tends to decrease with the galactocentric distance. Using the present and previous data of SiO maser surveys, we found that the local velocity gradient of the rotational velocity of the Galaxy is consistent with the values obtained from other kinds of disk population stars within a statistical uncertainty. The Oort's constants, A and B, were computed from the gradient of the rotation curve for the present data, and were consistent with the IAU standard values. In addition, in order to check the reliability of IRAS positions, we observed toward the MSX positions for 5 MSX counterparts, which are located more than 20″ away (but within 60″) from IRAS positions. We detected all of these 5 sources in SiO masers.