Light from celestial objects, when passing through the Earth's atmosphere,is subject to attenuation in °ux and change in spectral shape due to extinction which is caused by the effects of scattering and absorption by atmospheric particles and molecules. It is therefore essential to quantify the amount of extinction in order to measure the true radiation from celestial objects in ground-based as-tronomical observations in the optical band. Besides, on account of instrumental response, including telescope,detector and optical filter applicated in observation,transformed to the standard system is a necessary section. So, The measurement of atmospheric extinction of the site, as well as the determination of the transformations of the natural photometric system to the standard magnitude system,are among the basic calibration procedures for an astronomical telescope. In this thesis, I present preliminary results as part of our undergoing efforts to measure the atmospheric extinction and to calibrate the photometric sys-tem for the newly commissioned 2.4m telescope of Yunnan Observatory at the Gaomeigu observatory of Lijiang. For this purpose we have carried out observations at the 2.4m telescope, by observing sets of Landolt's standard star fields, in several observational runs in 2008-2009 in the U,B,V,R,I filters. I have systematically learned astronomical observations using telescopes and optical photometric data reduction and analysis. The reduction of the observed photometric data was performed using IRAF and the analysis of the data using IDL programming.As results, we derived the extinction coecients for the above 5 bands for some of the nights with acceptable data quality. We also give the mean extinction coefficients. Meanwhile, the transformations from the 2.4m photometric system to the standard magnitude system are also obtained for the five bands. In addition, two independent pieces of work are also presented. The first is on preliminary result of optical spectroscopic identication of the XMM-Newton X-ray Slew Survey sources which were observed in the SDSS spectroscopic survey.A small sample of seven new X-ray sources are identied, whose SDSS spectra are partly presented. They are all classied as active galactic nuclei, which were previously unknown. The second is a review on the detection of exoplanets and observational techniques, with the emphasis given to the LiJET project, an ongoing exo-planet project to be carried out at the Lijiang 2.4m telescope.
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