Shift of PRISM spectrum on MIDI detector
This effect, first pointed out in a memo
``Secular shift of spectra on MIDI detector''
by K. Tristram in May 2008, causes a problem for new data reduced with
the current version of MIA+EWS (1.6). This is because the sky windows
used to subtract a baseline from the chopped spectra are
misplaced
relative the the new position of the PRISM spectrum.
It is highly recommended to turn off the sky window baseline subtraction (dsky=99)
if using MIA+EWS 1.6 (or lower) for new data. A new version is to be released soon.
Meanwhile, MyMidiGui 1.6.1 already includes modified versions of utilities.pro,
mask_utilities.pro, and oirChopPhotoImages.c which enable the use of a (spectrum)
curve reference file that is fit to the observed spectra, and from which the sky
windows are offset by a fixed number of pixels. MIA's maskgui has been updated
and can be used
to verify the position of the sky windows with respect to
the spectrum and the edge of the field of view.
Christian A. Hummel
European Southern Observatory
Karl-Schwarzschild-Str. 2
85748 Garching
Germany
