The Photometric Techniques In Mutual Events Of Galilean Satellites

The photometry of mutual occultations and eclipses of natural planetary satellites can be used to infer very accurate astrometric data, which can be further used for improvement of the dynamical models and their ephemerides of the concerned satellites. This can be achieved by processing the light curves of the satellites observed during international campaigns of photometric observations of these mutual events. Emelyanov described and analyzed many light curves which derived from the images about mutual occultations and eclipses of the Galilean satellites during 2002-2003. However, the article did not elaborate on how to obtain the light curves from the images of mutual events, in this article the details of how to get the light curves from the images will be described and discussed.The photometry of the CCD images of mutual occultations and eclipses of the Jupiter's satellites which were observed with the 1-m telescope at Yunnan Observatory and Weihai Observatory in 2003 and 2009 was done and light curves in different situations were obtained. From a Gaussian function fitting to the light curves, the mid-light time and the falling magnitude were calculated in the mutual events.In the practice of image processing,the object satellite was in the halo of the Jupiter in many images and the photometry can't be measured accurately. Because of the good symmetry of the halo, the halo was removed symmetrically around the center of the Jupiter. In this thesis, an ellipse fitting method was used to measure the Jupiter's center and this method has been proved to have high precision in centering the disk of Jupiter. The background was quite flat after removing the halo and the aperture photometric can be made. It is also be found that the size of the apertures has great impact on the final light curves. Experimental results show that the light curves are stable when the photometric apertures are assigned between 1.5 and 4.0 times of FWHM of satellite's image. In the events of mutual eclipse, there are always more than one reference satellite in a frame, photometry for all reference objects should be measured to get better light curves.