LS-4825 - A BLUE SUPERGIANT ON THE FAR SIDE OF THE GALAXY

We present high-resolution spectroscopic observations of LS 4825, a V = 12 B-type star in the Galactic center direction. On the basis of its stellar and interstellar spectra, we infer that it is likely to be a young supergiant at a distance of 21 +/- 5 kpc, and hence lying on the far side of the 'Galaxy. Adopting this hypothesis, a differential abu ndance analysis shows LS 4825 to have a chemical composition that is c onsistent with local B-type supergiants. These observations therefore represent the first detailed investigation of a star on the far side o f the Galactic center. We trace multiple interstellar components in Ca II K and Na I D spectra, with velocities -206 less than or equal to v (lst) less than or equal to +93 km s(-1). We consider the likely origi n of this gas and find that some components appear to trace matter lyi ng close to the Galactic center. We discuss the possible use of such s ight lines in furthering our understanding both of the nature of gas a round the Galactic center and of the abundance gradient of the Galaxy.