Detection Of Faint Objects And Precise CCD Positions Of Galilean Satellite-pairs

In this paper we have done research on two aspects: Detection of faint objects betweenstreak-like stellar images and Precise CCD positions of Galilean satellite-pairs. On the one hand,we propose a novel method based on the characteristics of the object that we are interested in todistinguish it from other stars, whose images are line-shaped trails. The point-like object andstreak-like stellar images become more visible after some pre-processing, and operated byboundary tracking, and then they can be preliminarily identified by their form factors. Thecoordinates of the object on the CCD-frame can be further calculated by a two-dimensionalGaussian fitting in the original exposure. Experiment tests show that the new method candistinguish the object and other stars rapidly and precisely. The codes developed under theenvironment of Windows/Visual C++6.0can be applied to both a single exposure and series ofimages to identify an artificial satellite or space debris in motion.On the other hand, we present526precise CCD positions of Galilean satellite-pairs ofJupiter, which have been extracted from441CCD frames captured by a1-m telescope at theYunnan Observatory from2002to2010. The four Galilean satellites (Io, Europa, Ganymede andCallisto) are used to calibrate the CCD field of view by comparing their pixel positions with theirtheoretical positions computed from two modern ephemerides of the Galilean satellites, L2andJUP230, which have been developed by the Institut de Méchanique Céleste et de Calcul deséphémérides and the Jet Propulsion Laboratory, respectively. In this paper, we focus on therelative position of a pair of satellites with short separation (less than85arcsec) for good internalprecision. The mean (O C)(observed minus computed) values of all these satellite-pairs inright ascension and declination are found to be no larger than6mas and2mas, respectively, foreach ephemeris. The estimated precision for one single observation is better than30mas in eachdirection. This precision makes them comparable to currently the word’s most high-precisionobservations (the mutual events and space observations).