H-ALPHA DETECTION OF A CLUMP OF DISTANT HII-REGIONS IN THE MILKY-WAY

A group of 8 HII regions has been detected at a distance of 10 kpc fro m-the Sun at galactic longitude 298 degrees, using Ha wavelength obser vations. The observations were made with a scanning Fabry-Perot interf erometer to provide a detailed Ha: profile, which enables us to separa te these distant HII regions from the 3 other layers of ionized gas se en along the line of sight. A comparison of 5 GHz continuum and IRAS d ata allows us to analyse the nature of each source. Most of the distan t HIT regions were already known as radio sources or IRAS sources but one of them has no radio or IRAS counterpart. Inversely, IRAS sources without radio continuum nor an H alpha counterpart have been detected. Closer to us, on the same line of sight, we detected diffuse Ha: emis sion linking the Sagittarius arm with the Carina arm at a distance of about 2.5 kpc, where no usual tracer of spiral structure had previousl y been found. The HII region RCW 64, also seen in this direction, seem s to be located between the two main spiral arms.