AN H-II REGION BEYOND THE OPTICAL DISK OF THE GALAXY

The detection of a faint H II region at a kinematic distance of 28 kpc from the Galactic center is reported. The velocity and morphology of Halpha emission obtained using a Fabry-Perot indicate that the H II region is associated with a molecular cloud detected by Digel et al. (1993). The ionizing source must be close to the cloud and is constrained to be an early B star; a distant blue star, probably an early B supergiant, is identified as the ionizing star. Although its precise luminosity is uncertain, the likely range implies a distance modulus placing the H II region well beyond the optical disk of the Galaxy. Photometry of other stars associated with the GMC/H II region will allow a reliable distance determination and extend the rotation curve of the Galaxy by 60%. The implications of current star formation beyond the optical disk are discussed.