Observation of the Geocoronal Balmer Alpha with DEFPOS

Abstract

Instrumental improvements in sensitivity of Fabry-Perot spectrometers with the development of Charged Coupled Device (CCD) cameras enable measurement of faint emission lines. A Dual Etalon Fabry-Perot Optical Spectrometer (DEFPOS) has recently been built to observe hydrogen Balmer alpha ( Hα : 6563 Å) emission lines from the Earth’s upper atmosphere and the interstellar medium in our Galaxy. This spectrometer is now located at TUBITAK National Observatory (TUG), Antalya, Turkey, and has been observing in the zenith direction with a field-of-view of 4°.76 and with 1200 s exposure time. This paper briefly describes the DEFPOS spectrometer, data analysis, and results from data taken on 47 nights between 2002 and 2004. For the averaged geocoronal Balmer α intensities measured in nighttime, we found that the intensity was generally greater than 1 R and less than 12 R. These first results show that there is agreement with the theory and measurements made by other groups regarding the geocoronal Balmerα intensities. DEFPOS observations from Turkey offer potential to combine with geocoronal hydrogen observations at other locations such as Arecibo, Puerto Rico, Wisconsin Pine Bluff Observatory (PBO), and WHAM, Kitt Peak, Arizona, enhancing our global knowledge of the upper atmosphere. In the near future, DEFPOS will be used at coudé exit of the 150 cm telescope. Then, it will be able to make more accurate observations at any direction in the sky.

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