Image Shift-and-Add For Astrometry Of Jovian Faint Natural Satellites

The high precision measurements of natural satellites are of significance to the exploration of the origin,formation and evolution of the solar system.Among them,the natural satellite with higher brightness can obtain higher measurement accuracy by the traditional method.Faint natural satellites,they move fast,in the observation,if the exposure time is too long,the target image will appear a serious tail phenomenon,affecting the follow-up work.Therefore,it is impossible to obtain the image with high signal-to-noise ratio by simply extending the exposure time.Try to shift and add several CCD images with short exposures to improve the signal-to-noise ratio of the imaging of faint natural satellite,so as to obtain the highly accurate measurement results of faint natural satellites.The principle of image stacking has been studied in depth by predecessors,but no one has discussed the specific stacking method for moving faint natural satellites in detail until now,and no one has analyzed the astrometric results after stacking.In this paper,the implementation process of stacking images on faint natural satellite images is discussed in detail,and the measurement accuracy of the stacked objects is analyzed.In the shift-and-add process,each CCD image is shifted to align the stars in the field of view.In the process of displacement,Compared the transformation models including four constant model,six constant model,bilinear interpolation and cubic spline interpolation.It is found that the six constant model and bilinear interpolation have high performance in running speed and accuracy.For four consecutive nights in April 2018,229 images of Jupiter's five faint satellites were taken with the 1-m optical telescope at the Yunnan Observatory,the experiment and data reduction were carried out.At the same time,used the same measurements obtained from the Yunnan observatory's 2.4-m optical telescope at a nearby dates for comparison.In the position reduction,Gaia DR2 is used for our reference stars,and the Jet Propulsion Laboratory is usedfor the target theoretical position.The results show that by using the method of shift-and-add,the limit of the observation of faint natural satellite by 1-m telescope is increased from about16 magnitude to nearly 19 magnitude by stacking about 10 images with each exposure time of100 s,and the accuracy is better than 0.13 arcseconds,which is in good agreement with the measurement results of 2.4-m telescope.It can be concluded that the image shift-and-add technique applied to the measurement of faint natural satellites,can be used to detect previously undetectable targets by small-aperture telescopes with no less accuracy than large-aperture telescopes.