Images taken through the Kitt Peak Mayall corrector show a ghost donut near the middle; it is most pronouced in images taken through the interference filters, and at U and I. We need to get rid of the ghost pupil image in the flat fields, and we need to create a good ghost image pupil that we can use to subtract from our data.
We run both the combined dome flats and sky flats through mscpupil (with type=ratio) produces
ghost-free verions:
PACKAGE= mscred TASK = mscpupil input = domeU List of input images output = domeUp.fits List of output images (masks = BPM) List of masks (type = ratio) Output type (lmedian= no) Subtract line-by-line median? (xc = 27.) Pattern center offset (pixels) (yc = 9.) Pattern center offset (pixels) (rin = 300.) Radius of inner background ring (pixels) (drin = 20.) Width of inner background ring (pixels) (rout = 1500.) Radius of outer background ring (pixels) (drout = 20.) Width of outer background ring (pixels) (funcin = chebyshev) Inner azimuthal background fitting function (orderin= 2) Inner azimuthal background fitting order (funcout= spline3) Outer azimuthal background fitting function (orderou= 2) Outer azimuthal background fitting order (rfuncti= spline3) Radial profile fitting function (rorder = 40) Radial profile fitting order (abin = 0.) Azimuthal bin (deg) (astep = 0.) Azimuthal step (deg) (niterat= 3) Number of rejection iterations (lreject= 3.) Low rejection rms factor (hreject= 3.) High rejection rms factor (datamin= INDEF) Minimum good data value (datamax= INDEF) Maximum good data value (verbose= yes) Print information? (fd = ) (mode = ql)
We can now decide which type of flat does a better job of flattening our data by simply taking a few examples and running them through ccdproc.