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Hello,My Mosaic data taken from CTIO-4m on 2004 and 2005 seem have astrometry problem. MSCCMATCH seems run ok through them and the rms is less than 1.
But be dithered images could not be stack well, especially at the center of the image. By examining the individual images, I found that the same star have different RA and Dec (2-3 arcsec off) on different images, depends on which chip it landed on.I used the same process for the Mosaic data from year 2000-2003. They never had this problem and can be stacked well.Anyone encountered the same problem? What's the solution for this?Thanks!Ping Zhao

My experience with Mosaic (both the northern and southern) is that one
expects that the RMS of a fit is about 0.2-0.3". If it is significantly larger
than this, such as 1", chances are quite good that you are fitting noise or
confused identifications. If it helps any, have a look at how we reduced the Local Group Galaxies
Survey Data:
http://www.lowell.edu/users/massey/lgsurvey/splog2.html
specifically section 5.Hope this helps.---phil massey

Dear Phil,Thank you for your reply. I will try your way.Ping