The Space multi-band Variable Object Monitor (SVOM) is a proposed Chineseastronomical satellite, dedicated to the detection, localization andmeasurement of the gamma-ray bursts (GRBs) on the cosmological scale. Anefficient algorithm is developed for the purpose of onboard star extractionfrom the CCD images obtained with the Visible Telescope (VT) on board SVOM. TheCCD pixel coordinates of the reference stars will be used to refine theastronomical position of the satellite, which will facilitate trigger rapidground-based follow-up obsevations of the GRBs. In this algorithm, the image isdivided into a number of grid cells and the "global" pixel-value maximum withineach cell is taken as the first-guess position of a "bright" star. The correctcenter postion of a star is then computed using a simple iterative method.Applying two additional strategies, i.e., scanning the image only by even (orodd) lines or in a black-white chess board mode, are proposed to further reducethe time to extract the stars. To examine the efficiency of the aboveaglorithms, we applied them to the experimental images obtained with aground-based telescope. We find that the accuracy of the astronomicalpositioning achieved by our method is comparable to that derived by using theconventional star-extraction method, while the former needs CPU time about 25times less than the latter. This will significantly improve the performance ofthe SVOM VT mission.
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