Date: Mon, 7 Jul 2003 19:16:07 -0500 (CDT)
Subject: SPARO update #5


It's been four weeks since the last update that I wrote on June 10th.  
At that time, we were just starting to get data again after recovering
from the well-known computer problem.  Things have generally been
working well during the last four weeks, and we've been making steady
progress in our science program.

During these last four weeks, I estimate that we lost about 6-7 days due
to various equipment/software problems.  The most significant loss of time
was due to a failure in the SPARO data acquisition system.  It stopped
working shortly after I wrote the last update.  Paolo ended up having to
open up the SPARO Macintosh, pull out the DSP board, and put in the spare.  
That fixed the problem, but we don't know what caused the problem in the
first place.  Paolo, Bob, and Greg worked extremely hard on this, even
through the weekend, so down-time was kept to only 3-4 days.

We also lost smaller amounts of time due to various other computer
problems, some of which probably are residuals of the well-known
computer problem that occurred in early May, and the subsequent computer
rebuilds.  The computer system does seem to be somewhat fragile.  But
these computer problems are getting less and less frequent.

2-3 weeks ago, we had a failure of one of the FOS protection devices on
the az servo system, but Paolo found some spares and replaced the faulty
device, so this is back to normal.  Essentially no observing time was

The 350 micron opacity - "the tau" - has been very low (1.0-1.5) for most
of these last four weeks.  But we have found that low tau does not always
mean that we can get good data because the sky noise can have a
significant effect on the data.  There were several low-tau days when we
did not even take data because the sky noise was so bad.  There were also
long stretches of up to a week at a time when we were able to take
meaningful data, but the sky noise was bad enough to significantly degrade
our polarimetric signal-to-noise.  Then there are stretches when the sky
noise is gone or very low, and the polarimetric detections come more
quickly.  No strong correlation between tau and sky noise is evident.

Unfortunately, the 6-7 days that we lost due to equipment problems seem to
have been among the better days in terms of having both low tau and low
sky noise.  Because of this, I estimate that we could have had about twice
as much data during the last four weeks if there had been no
equipment/computer problems.  This estimate is somewhat uncertain as we
don't know for sure what the sky noise was like during the days we lost to
equipment/computer problems; we only know what it was like before and

Hua-bai is still working on sky-noise subtraction algorithms, so we may
yet improve the signal-to-noise on data that we have already acquired.  
Of course, this situation makes it hard for us to decide when to move on
to a new source, but we think we are doing a reasonable job with this. The
reason that we didn't have these sky noise subtraction algorithms in place
at the beginning of this winter is that we didn't see much sky noise in
winter 2000.  Now we know that this was probably just due to the low
optical efficiency that SPARO had in 2000.

We have now finished our second star formation target, that we call C4,
and we have a good start on our third star-formation target, C5.  C4 shows
levels of polarization of several percent and a lot of interesting
structure in the magnetic field.  I attach a map  (preliminary of 
course) showing these magnetic vectors.  It is significantly different from
Carina, so we still need to observe C5 and several others before we can
say something general about the role of magnetic fields in star formation.