Re: fits in channel space

Maurice,

   There is an ASCII input file format that load_data will
read (!).  Do

isis>  help load_data

...
  In the ASCII format, lines with a # symbol in column 1 are
     ignored and may be used for comments.

     The ASCII file may also contain keywords analogous to the
     header keywords in FITS files.  All keywords must be grouped
     together at the top of the file (possibly with interspersed
     comment lines).  Each keyword line must have a semicolon (;) in
     column 1 and may contain only one keyword name/value pair; a
     maximum of 1024 characters will be scanned on each such line.
     Only the first 8 characters of each keyword name are
     significant; the keyword name and keyword value must be
     separated by at least one space or tab character. Keyword
     values may be of type int, float, double or string; string
     keyword values may contain any printable characters including
     embedded whitespace characters (except newline). The supported
     keyword names are

     ___Keyname____Type____Definition_______________________

         object   string   source name
     instrument   string   e.g. ACIS-S or HRC-S
        grating   string   e.g. HETG or LETG
       exposure   double   exposure [sec]
           tg_m   int      diffraction order
        tg_part   int      e.g. HEG or MEG
       tg_srcid   int      source id number
          xunit   string   physical units of bin coordinates
        bintype   string   bin-value units; [counts|flux]

...

   -Dan

On Aug 3, 2009, at 2:22 PM, Leutenegger, Maurice A. (GSFC-662.0)[OAK  
RIDGE ASSOCIATED UNIVERSITIES (ORAU)] wrote:

> Hi,
>
> I have some uncalibrated laboratory data that I would like to fit  
> with isis. I can supply isis with columns of data that are like a  
> spectrum file: bin_lo, bin_hi, counts, and error. But the units of  
> the x-axis are not wavelength or energy; the data are in an  
> arbitrary channel space. I don't need to do anything particularly  
> complicated. I just want to fit Gaussians to calibration lines, so  
> that I can produce calibrated spectra.
>
> As far as I can tell, if I want to fit spectral data that's not in a  
> pha file, I need to use define_counts. Define_counts needs bin_lo  
> and bin_hi to be in wavelength units. This is not an option unless I  
> cheat. I could a.) use an approximate calibration to convert the  
> spectrum to wavelength, fit the calibration lines, and then convert  
> back to channel space; or b.) pretend that the arbitrary x-axis  
> units are really wavelength (but then it would be very far outside  
> of isis' normal wavelength range of operation).
>
> Anyway, I'm sure there must be a relatively simple way to do this,  
> but I don't know isis and slang well enough to have a guess. Any  
> suggestions? Thanks,
>
> Maurice

     ----------------------------------------------------------
     Daniel Dewey                           dd_at_email.domain.hidden     MIT Kavli Institute              Office:(617) 253-7244
     70 Vassar St., NE80-6085            Fax:(617) 253-8084
     Cambridge, MA 02139         http://space.mit.edu/home/dd
     ----------------------------------------------------------



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