Late-type Stars in the Inner Galaxy

Asymptotic Giant Branch (AGB) stars are good tracers of the Galactic structure. They are bright in the infrared and can therefore be detected even in the most obscured regions of the Galaxy. Maser emission from their circumstellar envelopes can be detected throughout the Galaxy, and reveals the stellar line-of-sight velocities with an accuracy of a few km/s. Our SiO maser survey of AGB stars was able to detect 255 new maser sources, thereby doubling the number of known stellar line-of-sight velocities toward the inner Galaxy. The longitude-velocity diagram of the SiO maser stars clearly reveals a stellar Galactic nuclear disk and suggests that they are related to the bar component. Using DENIS, 2MASS, ISOGAL, MSX and IRAS photometry, we can study the nature of the masing stars, deriving their luminosities and mass-loss rates, and establishing them as mostly variable AGB stars. In deriving extinction corrections from the surrounding field population colors, we were also able to constrain the near-infrared extinction law toward the inner Galaxy.