Date: Tue, 10 Jun 2003 12:34:53 -0500 (CDT)
Subject: SPARO update #4


This is the fourth update on SPARO 2003.  I wrote the last one in late
March, when we were just starting to do science.

We had very few problems in April.  As expected, the weather was not
good enough for submillimeter work during most of that month, but we did
observe for approximately 20% of the time, and we started getting
science results.  Then the came the well-known computer problem, on May
3, and it took us three and a half weeks to restore the computers to
full functionality.  On May 29th we started collecting science data
again, and we have been operating almost continuously since then.

To date, the integrated time spent doing polarimetry is about 16 days.  
This does not count time spent on the pointing checks that we do many
times per day, the photometric maps that we do in order choose our targets
(these maps are now mostly done), the time spent cycling SPARO, etc.

The main result is a very nice map of the magnetic field in the Carina
nebula - a star forming molecular cloud.  I attach a jpeg of this map,
showing vectors that indicate the magnetic field direction.  This is still
a very preliminary analysis, but it seems to show an "hourglass" or
"pinched" magnetic field geometry.  This geometry appears in scores of
theoretical papers, but has rarely been observed.  There are only two
published observations of such "pinched" magnetic fields, that I know of,
and they pertain to much smaller spatial scales than our Carina pinch.  
So I think that this result, if it holds up under more thorough analysis,
will be very interesting.

To say something general about the role of magnetic fields in star
formation, we need a larger data set.  We think that we have enough data
on Carina, and we have started on our second star-forming cloud.  We want
to observe a total of six star-forming clouds.  Hua-bai has picked out
these clouds, and we have mapped most of them photometrically (see under "Data Analysis").  Carina is by far
the faintest of the six.  In retrospect, Carina was not the best choice to
start on - I had thought it was probably in the top few clouds in terms of
being bright and extended, but I was wrong.  Given the current
improvements in weather, and the greater brightness of the remaining five
clouds, the star formation study could be finished in several weeks. Other
targets are the Galactic center and parts of the Boom-Pol Galactic field.

Viper is working well.  The pointing has been fine.  Last weekend we lost
the computer control of our mirror heating system.  Luckily, we discovered
that we can take data without this feature.  We simply leave the heat
switched on for all mirrors, and use the big HP's current limit knob to
regulate.  Regarding the main heater system, at present we are running it
using only the analog chassis.  We will fix all this eventually, but can
operate just fine in the meantime.

SPARO is working well.  We have verified the improvement in
signal-to-noise expected due to the 2001 optics upgrade.  For example, we
find that at the peak of Sgr B2, our signal is about five times bigger
than in July 2000, and our noise is unchanged.

Thanks very much to everyone who helped us to recover from the
well-known computer problem and other problems.  Everyone has stepped up
when asked to help.  It appears that our hard work is starting to pay