The fits located here are least square polynomial fits of the 225 Ghz and 350 micron CSO tau sky dippers. As the tau meters scan the sky every 10 minutes, they can produce noisy data. A single tau measurement can be a poor indicator of the actual tau. Thus, the tau stored in each scan may not be the most apropriate value to use in your reduction. As a helpful tool, these fits show the tau trends during the course of each evening and attempt to produce a tau value that is more realistic than the individual measurements.
The SHARC reduction tool, CRUSH, will automatically look at these
fits (if available) to obtain a tau value for use in reduction. The
user may opt to override this feature and enter a specific tau value,
or just use the tau value recorded in the FITS image header. Please
see CRUSH documentation for more information.
In order to obtain the best reduced data possible, these fits
must be used with caution. While they do an excellent job of
predicting the tau 90-95 % of the time, they are not perfect. Nights
with rapidly changing tau produce problems. On this page you will
find the analytic fits for both 225 Ghz and 350 micron data along with
a readme file for each. Further, plots are available for every
fit. To obtain accurate results, observers should inspect the nights
of their data and verify that the correct tau value is being
used.
A good place to start is the tau fit qualitative analysis
page. This page lists all the nights that SHARC II has been online. It
reports if 225 Ghz or 350 micron data is available for a particular
night and gives a qualitative analysis of the fit (including time
ranges that do not have a good fit).
Qualitative analysis of fits
Overview and Readme file for 350 micron tau fits
Overview and Readme file for 225 Ghz tau fits
225 Ghz fits
350 micron fits
The interested reader may also want to look at the JCMT/SCUBA polynomial fits.
To request fits for missing dates or request that a fit be redone contact John Vaillancourt (johnv_at_submm.caltech.edu).