There are several things I want to make sure before I start to do photometry on my drizzle-combined images.
1. If I choose cts as the pixel unit of my final drizzle combined image, is this in the units of electrons or ADU?
2. How is the final output drizzled image combined if I use EXP as type of weighting (median? average? or sum?). I am asking this because this is important in terms of determining the effective gain factor and readout noise of the final drizzle-combined image.
3. The "MDRIZSKY" keyword in the header of each input FLT image, is that the average sky value subtracted from each FLT file? According to drizzlepac handbook, if I were to do photometry with DAOPHOT, I need to add the sky value back to the image, so can I calculate the average value using MDRIZSKY from all input FLT files, and add that average to the final drizzle-combined image? For example, in pyraf, can I do:
hselect *_flt.fits MDRIZSKY yes | average
imcalc my_img.drz my_img_skyadded.drz "im1+sky_average"
4. Where to find the maximum good data value (the count level at which the detector saturate)?