PROFIT -- Implements the fitting method described in
1989, PASP, 101, 1032 for fitting the fractions needed
for optimal extraction when the spectrum is tilted or curved.
There are circumstances when extopt behaves poorly because the spectra
are too strongly tilted. This is when 'profit' followed by 'optext'
should be used.
In principle PROFIT should collapse with a dead-straight spectrum as the
linear equations become ill-conditioned. However I have yet to have it do
this and even on spectra tilted by less than a pixel it has been fine.
However you should keep an eye out if you are trying to apply it very
straight spectra. Use extopt if it does fail in such cases.
Parameters are:
IMAGE -- The data file under analysis.
FLAT -- balance frame.
DLOAD -- TRUE if dark frame is required.
DARK -- Dark frame representing counts unaffected by slit
profile. This will be subtracted off data before applying
the balance factors.
REGION -- Contains the sky/object region limits (only the object
limits matter in this case).
SKY -- Contains fits to the background sky in the region of
the object.
TRACK -- Contains fit to position of spectrum.
FRACT -- Output file containing fit evaluated over region of
extraction.
YSTART, YEND -- The Y pixel limits of the extraction.
READOUT -- The readout noise of the detector in RMS data units/pixel
PHOTON -- The number of photons per data number.
NPOLY -- Number of coefficients for profile polynomial fits.
Should not be more than 3 or 4 normally.
SIZEX -- The separation in pixels between the polynomials.
THRESH -- Sigma threshold for poly fits.
NSLOW -- Number of bad pixels to reject one by one. Standardly profit
rejects pixels in whole swathes. This parameter allows you to
force the safe-but-slow reject the single worst pixel at each
point. The larger you make it the safer it should be. For subtle
reasons, the safest values of this parameter are either 0 (which
gives standard old-style behaviour) or a large number like 100
BADVAL -- Value above which a pixel will automatically be ignored.
Use as a way of avoiding horrendous cosmics which can
upset 'profit'. Should obviously be way above any feasible
data values.
NBLOCK -- Data will be taken in groups of NBLOCK rows.
NMED -- Low signals with large numbers of cosmic rays can go completely wrong
owing to the profiles with cosmic rays in them being given EXTRA weight. e.g.
if the total signal is typically 100 counts but a cosmic rays comes
along with 10000 counts, that profile looks particularly good. To reduce
this, this option median filters the profile sums before they are divided
in to estimate fractions. Should not be too wide if target has lots of
narrow line features. Must be odd. thsi number can be traded against NBLOCK
to some extent.
PLOT -- TRUE to make plots.
DEVICE -- Plot device
This command belongs to the classes: extract , fitting , tilted