iraf.net

[color=red:c1429c0040][Moderator's Note: Posted on behalf of user ghang.naoc@gmail.com] [/color:c1429c0040]hi all,
I need to do photometry for program ID GS-2010B-Q-63 by Gemini-S.
Now I meet some problems which confuse me much.Could someone please help me?
I pick out four fits from the archive data.You can download them from
http://www3.cadc-ccda.hia-iha.nrc-cnrc.gc.ca/cadcbin/gsa/gsaDsscAttr.pl a raw G band image A:S20100802S0035.fits
the corresponding calibrated image B:mrgS20100802S0035_add.fits
I just found one bias and one flat C:gS20100802S0072_bias.fits
gS20100814S0019_flat.fits Q1 GAIN
http://www.gemini.edu/?q=node/10426
Gain values of the two fits A and B are 1.89,2,3.I get it from the fits header.Generally the header info is right,right?The gain values change after calibration?And they are not included in the link above.I notice that there are gain values higher than 11 for some fits.
Q2 pixel scale
It should be 0.073arcsec/pixel,right?Why are the pixel scale of both of the two fits is 0.146arcsec/pixel?The raw image is binned too?
Q3 pixel value
why are the pixel vales of B higher than A,since mrgS20100802S0035_add.fits=(
S20100802S0035.fits-bias)/flat?
Q4 Since the pixel number of A is different from C and D?How to know which pixel of A corresponds to which pixel of B and C?