Subject: Re: dust shutdowns

From: Eric Deutsch

Submitted: Mon, 6 Oct 97 15:49:54 -0700

Message number: 185 (previous: 184, next: 186 up: Index)

Let me point out that I have added a new feature to the "Weekly Plot" at the
bottom of my "Weather Plots" WWW page:
http://www.astro.washington.edu/deutsch/apoinfo/cloudscan/weatherplot.html

The mean and median 1.0 micron dust counts for the past 7 nights (yes,
nighttime only!) are printed at the top of this weekly data plot.  For
example, today the mean is about 5500 particles per cubic foot (note
that this unit is 10x the raw numbers seen from the instrument!).
Perhaps a strategy of closing the telescope when the the observed value
of dust counts is some factor of the mean for the past week would be
more appropriate than closing at an arbitrary value (16000 PpCF is the
current value, as I understand it, which is ~3x last week's mean).

For example, when the dust counts increase to 10x the mean for the past
7 nights (and one estimates that a night is 10 hours long, and that the
dust accumulation rate is proportional to the dust density) one might
think that the mirror is saved from a night's worth of contamination
for every hour that the dome remains closed.

At some point in the near future, I hope to investigate the situation a
little more closely and/or provide a tidy dataset for other folks to play
with.  However, one item which might be helpful to stir into a simulation
for addressing this problem is the exact times that the dome is open
(and if not, why not!).  Does someone have easy access to a database
furnishing this information, and if not, maybe we ought to keep one.

Eric


----------------------------------------------------------------------
Eric Deutsch                       email: deutsch@astro.washington.edu
Department of Astronomy                          Voice: (206) 616-2788
University of Washington                           FAX: (206) 685-0403
Box 351580               WWW: http://www.astro.washington.edu/deutsch/
Seattle, WA  98195-1580            Physics/Astronomy Bldg., Room B356F



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