From: 	Daniel A Dale <ddale@uwyo.edu>
Date: 	Mon, 09 May 2005 10:03:05 -0600	

Rob,

It turns out that the coordinates we used for NGC 2403 extranuclear
targets were a bit off.  Sangeeta did caution us that there were some
slight displacements in the optical coordinates from the ISOCAM 15
micron coordinates, but she didn't know if those displacements were due
to astrometry error or physical differences.  Unfortunately for the case
of NGC 2403, I didn't double check her work.

I checked several locations using IRAC, DSS, and our H-alpha image. 
Perhaps Sangeeta used our H-alpha image: the coordinates in the H-alpha
image are off by about the same amount our extranuc pointings are off:
between 5 and 9" E and between 5 and 9" S.

The impact is quite small for our LH maps, since they are so large
(~45"x33").  The impact for the SH and SL maps is higher, but somewhat
hard to quantify since these HII regions are rather extended.  Our map
centers are 5-9" E and 5-9" S of the brightest knot in each HII, but
they do capture a lot of interesting extended emission. 

In the attached jpg (IRAC 8.0 microns, plus extranuc map overlays), you
can can start to get a feel for the situation.  JD and I will try to
clarify the situation by looking into the actual maps created by CUBISM.

Danny