Not totally within CIAO, but I have an easy suggestion: Pull up your image
in DS9. Turn on the contours feature, and select your preferred contour
level; save the contour region, and use it to extract a spectrum for the
bright features. Then exclude the region to extract the faint spectrum.
The difficulty is that these contours apparently can't go to zero
smoothness, but then your objects probably aren't exactly square-edged either.
> Hi all,
> I have some ACIS data of a complicated extended source. I have reason to
> believe that the bright regions and faint regions have different spectra,
> and would like to see if this is indeed the case.
> One thing I can do is draw boxes around all the bright areas by hand,
> and then extract the appropriate spectrum. But does anyone know if
> there is a way within CIAO to extract a spectrum from an event file
> corresponding to those pixels in the image which are brighter than a
> certain threshold? I.e. is there I way I can get the spectrum only of
> those image pixels with (say) >10 counts in them?
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