Summary of dicussion during chop-nod analysis telecon of Jan 23, 2008

Hiroko, Lero, Mike, John, Giles

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M82 analysis:

We discussed Lero's continued work on the data from April 28th.  

The hwp angles look fine (within 3 degrees) for all files except those
that are marked in the excel log as having bad hwp angles.  This was
established with readsharc.  Lero points out that it would be good to have
access to the actual numbers, not just the plot.  John says that this is
possible with a simple IDL command, but notes that there will be a lot of
numbers to scan through as they all get dumped to the screen.

The "grading" of the I images shows that most are fine ("0") but about a
third were graded as being questionable ("1").  When John and Giles looked
at the files that Lero graded as "1", some (or perhaps all) were judged to
be OK.  Lero will revisit.

Giles pointed out that when using ds9 on a color scheme the bad pixels
show up as looking very different from all the others.  But with fv, this
seems not possible, making it hard to judge the images.

John argued that, while the -w flag is good for getting a sense of the
data quality from the I images (and, of course, for developing pointing
corrections), it is probably safest to NOT use this flag for the
polarimetry analysis.  (I.e., after doing the pointing corrections and
"data editing", rerun sharpinteg_2 *without* this flag.)  We agreed.

Some next steps for Lero's analysis of late July M82 data:

regrade the I
grade the Q and U (with Giles' help)
do the pointing corrections (with Mike's help)

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Reduced-chi-squared procedures:

The concerns raised two weeks ago (see posted summary) turned out to be
symptoms of a bug: The NaN's from sharp_combine output are not being read
correctly by Mike's "c" routines.  They are being read as very small
numbers rather than NaN's.  One work-around would be to read John's Mask
image, but this does not work as John uses additional criteria to reject
data-points and replace them with NaN.  So instead Mike discriminates
between NaN and regular numbers by treating any number that is
sufficiently small as an NaN.

Mike is planning on computing the reduced-chi-squared not just from the
region where all bins have data, but instead using all regions where more
than one bin has data.  Giles thinks this is fine, in principle.

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The following items were not discussed on the telecon:

Mike's plans to make a smoothed tau for November 2007 

linked list-serves for SHARP (Giles action item)

i.p issues (specifically 450 micron i.p. and Jan 2006 i.p.)

alternate ideas for telecon - iChat on Mac

postscript problems on Lero's Mac and on kilauea, and Hiroko's
investigation of the kilauea problems.  In any case, I guess these are
solved.

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