Re: fits in channel space

From: David P. Huenemoerder <dph_at_email.domain.hidden>
Date: Mon, 3 Aug 2009 14:35:56 -0400
Hi Maurice, 

    Leutenegger> to be in wavelength units. This is not an option
    Leutenegger> unless I cheat. I could a.) use an approximate
    Leutenegger> calibration to convert the spectrum to wavelength,
    Leutenegger> fit the calibration lines, and then convert back to
    Leutenegger> channel space; or b.) pretend that the arbitrary
    Leutenegger> x-axis units are really wavelength (but then it would
    Leutenegger> be very far outside of isis' normal wavelength range
    Leutenegger> of operation).

Don't consider it cheating!  The only restriction is that the
x-coordinate not be <=0.  But even that can be worked with an offset.
I have used isis to fit lines shifted to velocity space.

    Leutenegger> Anyway, I'm sure there must be a relatively simple
    Leutenegger> way to do this, but I don't know isis and slang well
    Leutenegger> enough to have a guess. Any suggestions? Thanks,

define_counts will work w/ appropriate grids and errors.

Don't assign arf, rmf (unless you define an arf, for instance to be
some other arbitrary scale factor).

Then you can use fit_fun and fit_counts.

If you have real-valued data, you can use define_flux(), fit_flux()
instead.


Also note that isis supports "metadata"; see the help for
set_dataset_metadata(); this is where you could put any x-axis offset,
for instance.


-- Dave

David Huenemoerder  617-253-4283 (o); -253-8084 (f); http://space.mit.edu/home/dph
MIT Kavli Institute for Astrophysics and Space Research
70 Vassar St., NE80-6065,
Cambridge, MA  02139
[Admin. Asst.: Elaine Tirrell, 617-253-7480, egt_at_email.domain.hidden
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Received on Mon Aug 03 2009 - 14:35:58 EDT

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