An improved solution to geometric distortion using an orthogonal method
  The geometric distortion of CCD field of view has direct influence on the positional measurements of CCD observations. In order to obtain high precision astrometric results, the geometric distortion should be derived and corrected precisely. As presented in our previous work Peng et al. (2012), a convenient solution has been carried out and also been made with successful application to Phoebe's observations. In order to further improve the solution, an orthogonal method based on the Zernike polynomials is used in this work. Four nights of CCD observations including Himalia, the sixth satellite of Jupiter, and open clusters (NGC1664 or NGC2324) on each night have been processed to make an application. The observations were obtained from the 2.4 m telescope administered by Yunnan Observatories. The catalog UCAC4 was used to match reference stars in all of the CCD frames. The ephemeris of Himalia is retrieved from the (IMCCE). Our results show that the means of observed minus computed (O-C) positional residuals are -0.034 and -0.026 arcsec in right ascension and declination, respectively. The corresponding standard deviations are 0.031 and 0.028 arcsec. The measurement dispersion is significantly improved than that by using our previous solution. 
Huan-Wen Peng, Qing-Yu Peng and Na Wang
astro-ph.IM astro-ph.EP