Defpos: Design, performance characteristics and first results

Fabry-Perot spectrometer has been built to observe faint optical Ha emission line from the diffuse ionized hydrogen gas in our galaxy. The spectrometer has been called DEFPOS (Dual Etalon Fabry Perot Optical Spectrometer) and it has consisted of two 7.5 cm diameter Fabry-Perot etalons. A CCD (2086x2048 pixels)with high quantum efficiency (%78 at Ha) has been used as a detector. Resolving power of the DEFPOS has been measured as 11000. DEFPOS has been located at Bakirhtepe and it has directly looked at zenith direction with 4.76° field of view. We have observed and observe geocoronal and galactic Ha emission lines in this direction with 1200s exposure time. It has been collected 545 H a spectra, between 30 September 2002 and 21 September 2003 within 27 nights. All the data has been analyzed and geocoronal Ha and ionized hydrogen intensities and their velocity with respect to LSR has been determined. Key Words: Fabry-Perot Spectrometer, Interstellar Medium, Hû Regions, Geocoronal Hydrogen Balmer-a Emission