Period Measurement of AGB Stars in the Outer Galactic Disk

The light variation of the 47 AGB star candidates in the outer galactic disk has been monitored at the I-band for 5 years. Periods were well determined for 18 of them, and less reliably for the other 25. The average period of the objects is then 500 days. According to the period-luminosity relation, the mean luminosity of the sample stars is 10000 LO . Based on the absolute luminosity, derived from the period-luminosity relation and the apparent luminosity from the observation, the distances to the objects were determined. The calculated distances are slightly greater than those obtained previously based on the assumption of a constant luminosity of 8000 LO . In addition, SiO maser emission was detected for most of the observed objects, so that their radial velocities were accurately known. With the assumption of circular rotation in galactic disk, the rotation curve and Oort's constants were derived.