Important notes for users
The program needs bias-subtracted, flat-fielded, unskysubtracted
images. Flatfielding is usually not critical, bias subtraction is!
If the sky was subtracted from an image, the program will add the
sky back in if skyval>0.
For long slit data the program offers the option of subtracting the sky
and/or the objects before identifying cosmic rays. These fits are
strongly recommended - in particular fitting the sky
lines. The order of the sky line fit depends on the size of the image;
typical values are yorder=2 for y < 50, yorder=3 for
50 < y < 80, and yorder=5 for y > 80. The sky subtraction is time
consuming: if only part of the spectrum is of interest it will help
to cut out the relevant image section.
The processing time is approximately proportional
to the number of pixels; scale from 1 minute per iteration for an
800x800 image on an Ultra1 (200 MHz).
For users with no access to IDL and no experience with IRAF (assumes
image is in fits format):
- make sure iraf is installed and you have a directory with a login.cl
- if not, type 'mkiraf' and/or ask system management
- edit the login.cl file: add/uncomment line "set imtype=fits"
- make sure this line does NOT read "set imtype=fits,noinherit" (is the
case in some IRAF installations)
- start iraf by typing 'cl' in the directory where the login.cl resides
- type 'stsdas'
- if error message: ask system management to install the stsdas package
- type 'task lacos_im = path/lacos_im.cl' where path/ is the path to
the script you downloaded
- edit the parameters by typing 'epar lacos_im'
- get out of the editing mode using CTRL-D
- start lacosmic by typing 'lacos_im input output outmask'