Giles
asked that I take the same Orion files that Hua-bai used for his recent
Orion map and run them through the current version of our Hertz-mode software. (See Hua-bai's results for comparison.)
This contains 3 polarization scans (files 028583 - 028586, 87-90, and 92-95)
with parallactic angles -3.4 -- +4.0 degrees and telescope elevations
of 65.05 -- 65.03 degrees, tau225 ranges from 0.049 - 0.054. I think
the results are very promising.
These were run through the latest version of sharpinteg (dated 2006-Apr-13) and sharp_combine (v2.2). Sharp_combine takes into account the sky and telescope rotation and any applied pointing offsets, and corrects for atmospheric opacity (using the header tau225 value). I used the HWP offset angle of +32 degrees.
In sharp_combine I smoothed the I-image with a gaussian kernel of FWHM 2 arcsec and a cutoff radius of 5 arcsec. The q and u images were smoothed with a 5 arcsec FWHM and 5 arcsec cutoff radius.
In the attached figure I have only plotted every
4th vector (that is the vector at every 4th pixel, the pixel size
is ~2.4 arcsec). The polarization signal to noise ranges from 4 --
20, with polarizations of 0.6 - 4.7 % (median = 2.1 %). The median
polarization angle is 21 degrees E of N.
I have
carried out the same operation for the files in which the pointing was
offset 20 arcsec to the south of Orion-KL (4 polarization scans in file
numbers 28825 - 28840).
Combining
both pointing sets yields the image at right.