Wavelength Solutions in GMOS MOS spectra (script to fit specific sci extensions)

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    When doing MOS data reductions, one of the tedious steps can be solving for the wavelength solutions and transformations, especially when there are lots of slits and the MOS slit lengths vary wildly, and thus the xorder/yorder transformations need to be tuned for individual slits.

    The automatic (fl_inter=no) wavelength solution in gswavelength is pretty good, and I have found that the most efficient way to do the MOS reductions is to make a first pass of gswavelength non-interactively, then apply the transformation to the arc spectra, and visually inspect (with gdisplay & imexam) the output to make sure that things worked out. Often, I’ll find that for 80+% of the slits, things were great, and just a couple of slits failed.

    The question then is how to most efficiently fix the fits for those slits that failed. The standard gmos reduction scripts don’t allow you to select which extensions to fit; they just loop over all the extensions. I’ve modified the gswavelength script to add a couple of parameters allowing you to select a subset of extensions. That script is attached here as “mgswavelength.cl” The new parameters are called “firstsciext” and “lastsciext”. If these parameters are set to 0, then all the mdf rows will be fit
    (except for the acquisition objects). If you set them to some
    non-zero value, then it will only fit the science extensions
    requested. Note that it actually is the number of the science
    extension, not the mdf row, and there might be a difference of 2 or 3
    between those values. So, for instance, I set firstsciext=lastsciext=7, and
    it fit extension 7, which is MDF row 10.
    To define this task, put the script into some directory, for
    instance /usr/marcel/bin or whatever. Then inside iraf type “task
    mgswavelength=/usr/marcel/bin/mgswavelength.cl”. If it worked
    properly, you should be able to type “lpar mgswavelength” and see the
    full parameter list.

    When you run mgswavelength to fix errant automatic solutions, make sure that the interactive flag is set to yes (fl_inter=yes), and that the overwrite flag is also set to yes (fl_overwrite=yes).

    Please comment on this thread, or contact me directly if you have any questions or problems.


    • This topic was modified 12 months ago by achene achene.
    1. mgswavelength.cl
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