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 A) 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 coude exit of the 150 cm telescope. Then, it will be able to make more accurate observations at any direction in the sky.
Highlights
The exosphere and the upper thermosphere, called the geocorona, is the uppermost region of the earth’s atmosphere characterized by low densities long, mean free paths, and non-Maxwellian velocities (Chamberlain 1987; Chamberlain and Hunten 1987)
It has been designed to be used at the coudé focus of the 150 cm telescope installed at TUG, but since the coudé exit of the telescope was not ready at that time, the spectrometer was set up in a room on the upper floor of the telescope building, and observations began in the zenith direction in October 2002
Since the resolution of Dual Etalon Fabry-Perot Optical Spectrometer (DEFPOS) is 11000, which corresponds to instrumental line width of 27 km s-1, and the line width of the geocoronal Hα line is around 7 km s-1, it is impossible to determine the temperature of the geocoronal hydrogen line with this resolution
Summary
The exosphere and the upper thermosphere, called the geocorona, is the uppermost region of the earth’s atmosphere characterized by low densities long, mean free paths, and non-Maxwellian velocities (Chamberlain 1987; Chamberlain and Hunten 1987). Fabry-Perot observations have been made continuously both at the Arecibo and Wisconsin sites since the early 1980s (Meriwether et al 1980; Shih et al 1985; Yelle and Roesler 1985; Kerr et al 1986; Kerr and Hecht 1996; Nossal et al 1998, 2001). Similar to these two groups, we have designed and built the DEFPOS (Dual Etalon Fabry-Perot Optical Spectrometer) to measure Balmer α emission from the geocorona and the interstellar medium of our Galaxy (Sahan et al 2005). We introduce the spectrometer itself and present the very first results of geocoronal measurements obtained with it
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