Studying the Galactic Bulge Through Spectroscopy of Microlensed Sources: II. Observations

The spectroscopy of microlensed sources towards the Galactic bulge provides a unique opportunity to study (i) the kinematics of the Galactic bulge, particularly its far-side, (ii) the effects of extinction on the microlensed sources, and (iii) 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 European Southern Observatory (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. It is shown that there is an extinction shift between the microlensed population and the non-microlensed 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.