[AstroPy] HST photometry

[gonghang.naoc]

Hi guys,

 Maybe it is not very relevant to the subject here.I am wondering anybody
ever done hst photometry here?I have read dolphot's manual but it is too
terse.Could anybody give me some quick help on the questions below？I have
downloaded c0m and c1m files from stsci.
    cosmic ray problem:There is  a command crrej and it has parameters like
dx and dy.The 2 parameters are powerful enough？We should align the images
before cosmic ray rejection?
If  one filter has more than one exposures we can combine the images to do
photometry.So it should be which step?After cosmic ray rejection?
    astrometry problem:It is the last step just before the workhorse of the
DOLPHOT package dolphot?DOLPHOT can not deal with that,right?Is there any
reliable python way to do that?

Any method except dolphot is welcome.

Thanks,

Hang
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