Resolving the Kinematic Distance Ambiguity toward Galactic H II Regions

The spectroscopy of microlensed sources toward the Galactic bulge provides a unique opportunity to study (1) the kinematics of the Galactic bulge, particularly its far side, (2) the effects of extinction on the microlensed sources, and (3) the contributions of the bulge and the disk lenses to the microlensing optical depth. We present the results from such a spectroscopic study of 17 microlensed sources carried out using the ESO Faint Object Spectrograph (EFOSC) at the 3.6 m ESO Telescope. The spectra of the unlensed sources and Kurucz model spectra were used as templates to derive the radial velocities and the extinctions of the microlensed sources with respect to the unlensed sources. There is an extinction shift between the microlensed population and the nonmicrolensed population, but there is no apparent correlation between the extinction and the radial velocity. This extinction offset, in our best model, would imply that 65% of the events are caused by self-lensing within the bulge. The sample needs to be increased to about 100 sources to get a clear picture of the kinematics of the’bulge.