Investigations of geocoronal hydrogen alpha emission with DEFPOS

A 7.5 cm dual etalon Fabry-Perot spectrometer called DEFPOS (Dual Etalon Fabry-Perot Optical Spectrometer) has been developed and located at TUBITAK National Observatory (TUG: Antalya/Bakırlıtepe) to observe faint optical emission lines from the earth?s upper atmosphere and from interstellar medium in our Galaxy. Total 448 H alpha data were taken on 21 nights with 4.76 field of view in zenith direction at 1200 s exposure times between 2002-2004. In this study, to determine geocoronal Balmer alpha intensity depending on solar depression angle (SDA) and shadow height (SDWH) , all data were analyzed and then galactic H alpha lines were removed from each individual data. For the averaged geocoronal Balmer ? intensities measured in nighttime, we found that the intensity was generally greater than 1 R and less than 12R. These first results show that there is agreement with the theory and measurements made by other groups regarding the geocoronal Balmer alpha.After completed test observations through the zenith direction the spectrometer has been newly redesigned for coude observations in 2007 and then set up at the coude exit of the telescope to detect and study the faint optical emission lines from selected HII regions and planetary nebulae with small angular size near 4 arcmin FOV.