Rolling your own

The COSMOS software does not do everything, and may very well not do the things it does the way you would like. If you would like to customize the processing, a good starting place would be with the output of adjust-map. The mapfile produced by adjust-map provides all the information you need to extract the spectral data, using any method you may chose. The information necessary to locate any wavelength and slit position is given as a set of polynomials.

The mapfile has the following format:

Xdispersion = dirflat
Fit orders = ord_disp ord_sag ord_tilt ord_sagit ord_len
Scale ~ telscale
Lambda = lamin lamax

SLIT slitnum objectname
LENGTH = slitlength
CHIP chipnum slmax slmin lammin lammax
dispersion polymonial
inverse-dispersionn polynomial
sag polynomial
tilt polynomial
sagitta polynomial
slit-length polynomial
CHIP chipnum slmin slmax lammin lammax
.
.
.

SLIT slitnum objectname
.
.
.
END

The first 4 lines give general parameters:

Xdispersion = dirflat

.dirflat = 1 if the dispersion is along the x direction of the chips (i.e. along the rows), otherwise dirflat = 0.

Fit orders = ord_disp ord_sag ord_tilt ord_sagit ord_len

ord_disp	order of the dispersion fit, and the inverse dispersion fit
ord_sag	order of the spectrum "sag" fit
ord_tilt	order of the spectrum tilt fit
ord_sagitta	order of the slit curvature fit
ord_len	order of the slit length fit

Scale ~ telscale.

.Image scale at ccd focal plane. (Hard-wired into map-spectra.)

Lambda = lamin lamax

.minimum and maximum wavelengths of spectrum fits in this file

For each slit, there is a line:

SLIT slitnum objectname

.slitnum is the sequence number, and objectname the name given in the SMF file

Only well-behaved slits have the following data. A well--behaved slit is one in which both ends of the slit fall onto the same chip (the spectrum may well span several slits in the dispersion direction).

LENGTH = slitlength

.slitlength is the nominal length of the slit, in pixels

for each chip that the spectrum traverses, the following data is given:

CHIP chipnum slmax slmin lammin lammax npixels

chipnum	chip number
slmin	distance to "left" end of slit from object, in pixels
slmax	distance to "right" end of slit from object, in pixels
lammin	minimum wavelength of spectrum on this chip
lammax	maximum wavelength of spectrum on this chip
npixels	length of spectrum on this chip, in pixels

fit of lambda vs pixel coordinate in the dispersion direction and the inverse fit of pixel
                       coordinate vs lambda

fit of pixel coordinate of the object perpendicular to the dispersion direction (i.e. along the
                       slit. Note that this is equal to the slit center only if the mask design places the object midway along the
                       slit.