DETECTION OF IONIZED-GAS TOWARD AN OH IR STAR - A MEASURE OF THE UV-RADIATION FIELD NEAR THE GALACTIC-CENTER/

The nature of the ionizing UV radiation field in the inner Galaxy is i nvestigated by searching for radio continuum emission from the outer e nvelope of the population of OH/IR stars toward the Galactic center re gion. Radio continuum observations of a sample of OH/IR stars have bee n made at 3.6 cm using the VLA in its A, B, and DnC configurations. A highly scattered OH/IR star has been detected with a flux density of s imilar to 1 mJy, which suggests that the star is photoionized by an ex ternal radiation field. The UV flux responsible for ionization is esti mated to be 2.5 x 10(9)(M(-5))(-4) photons cm(-2) s(-1), where M(-5) i s the mass-loss rate in units of 10(-5) M(circle dot) yr(-1). We note that the continuum emission should become optically thick below a few hundred megahertz and that measurements at these frequencies will be a ble to determine both the UV flux and M.