HIGH-RESOLUTION SPECTROSCOPY IN THE FAR UV - OBSERVATIONS OF THE INTERSTELLAR-MEDIUM BY IMAPS ON ORFEUS-SPAS

The Interstellar Medium Absorption Profile Spectrograph (IMAPS) is an objective-grating, echelle spectrograph built to observe the spectra o f bright, hot stars over the spectral region 950-1150 Angstrom, below the wavelength coverage of HST. This instrument has a high wavelength resolving power, making it especially well suited for studies of inter stellar absorption lines. Following a series of sounding rocket flight s in the 1980's, IMAPS hew on its first Shuttle-launched orbital missi on in September 1993, as a partner in the ORFEUS-SPAS program sponsore d by the US and German Space Agencies, NASA and DARA. On ORFEUS-SPAS, IMAPS spent one day of orbital time observing the spectra of 10 O- and early B-type stars. In addition to outlining how IMAPS works, we docu ment some special problems that had an influence on the data, and we e xplain the specific steps in data reduction that were employed to over come them. This discussion serves as a basic source of information for people who may use archival data from this flight, as well as those w ho are interested in some specific properties of the data that will be presented in forthcoming research papers. IMAPS is scheduled to fly o nce again on ORFEUS-SPAS in late 1996. On this flight, 50% of the obse rving time available for IMAPS and two other spectrographs on the miss ion will be available to guest observers.