High Precision Positional Measurement For Uranian Faint Satellites

High precision position measurement of the solar satellites can improve the accuracy of satellites ephemerides and improve the orbit theory of the satellites,which can serve for future space exploration mission,and it is also important for the researches of the Solar System formation and evolution.Uranus have five major satellites,the position of Miranda were more difficult to obtain since the faint satellite is close to the planet and usually embedded in the primary's halo light.In order to improve the measurement accuracy of the faint satellites,we use the Gaussian function with Polynomial background to develop a position measurement system for the faint satellites near the planets,and apply it to Uranian faint satellite Miranda position measurement experiment.150 CCD frames of Uranus and its satellites were taken by a 1-m telescope at the Yunnan Observatory on November 21 and 23,2016.We use the two to six order polynomial to measure the position of Miranda.The recently released catalogue Gaia-DR1 was chosen to match reference stars.Our results show that the mean(O-C)s(observed minus computed)are 0.008 and-0.007 arcsec in right ascension and declination,respectively.The standard deviation are 0.023 and 0.020 arcsec in right ascension and declination,respectively.At the same time,we have made a detailed comparison and analysis of the measurement results for different order polynomial models.We have found that for the good signal-to-noise ratio observation data,the two-order polynomial and Gaussian function can get a good result for the faint satellites near the planets,three or four-order polynomial can get higher precision than the two-order model,the more higher order polynomial can not improve the accuracy further.Moreover,we have researched where the situation can we use the Gaussian function with Polynomial background method.In order to get higher precision position,when the satellite is not very close to the planet we can use the two-order polynomial,when the satellite is very close to the planet we need to use higher order polynomial,such as the four-order polynomial.This method have some limitations,which can not improve the measurement accuracy of the observation datawith low signal-to-noise ratio.The limitations maybe resolved by remove the contaminated background by the halo light from the planet.Therefore,our next work will to research remove the halo light from the planet.