The Wisconsin Hα Mapper (WHAM): A Brief Review of Performance Characteristics and Early Scientific Results

The Wisconsin H α Mapper (WHAM) is a recently completed facility for the detection and study of faint optical emission lines from diffuse ionised gas in the disk and halo of the Galaxy. WHAM consists of a 15 cm diameter Fabry–Perot spectrometer coupled to a 0·6 m ‘telescope’, which provide a 1° diameter beam on the sky and produce a 12 km s −1 resolution spectrum within a 200 km s −1 spectral window. This facility is now located at Kitt Peak in Arizona and operated remotely from Madison, Wisconsin, 2400 km distant. Early results include a velocity-resolved H α map of a 70° × 100° region of the sky near the Galactic anticentre, the first detections of H α emission from the M I and A high velocity clouds, and the first detections of [O I] λ6300 and other faint ‘diagnostic’ lines from the warm ionised medium. Through the summer of 1998, WHAM will be devoted almost exclusively to a survey of the northern sky, which will provide maps of the distribution and kinematics of the diffuse HII through the optical H α line in a manner that is analogous to earlier sky surveys of the HI made through the 21 cm line.