20010320 report
Empirical correction tested, twice
Grade 3 weather was used to check the empirical correction installed
on 20010314.
The
map16 method
was used with Mars as the source :
- from (az,el) = (157,45) at HST 04:18 to (210,42) at 07:04
- transit occurred at HST 05:29 at an elevation of 48 degrees.
The seeing was between 0.6" and 0.9".
The pointing residuals are displayed below :
The azimuth performance is reasonable, with an rms scatter of 0.6".
The elevation residuals show a 2" undercorrection at azimuth 185
and a 1.5" overcorrection at azimuth 195, with an apparent mid point at
azimuth 190. I would not have expected errors in excess of 1"
from the fit to the data from 20010314 -
see the plotted residuals from
those data -
so this is rather surprising, and at worst suggests further evolution
of the defect.
22 Mar 2001
A further test was done this morning using 3c279 :
- from (az,el) = (159,63) at HST 00:39 to (211,60) at 02:18
- transit occurred at HST 01:18 at an elevation of 64 degrees.
The seeing was recorded as 0.4" while tau_cso was approximately 0.18.
The pointing residuals are displayed below :
The rms scatter in each coordinate is 1.0".
There is a weak similarity in the behaviour of the elevation residuals
inasmuch as they show excursions at azimuths 185 (+ve) and 195 (-ve) as
before, but this effect is of magnitude 1" today and is comparable to
probable atmospheric effects. (There is no other way to explain
the strong azimuth excursion at azimuth 190). With this caveat
the data do not replicate the excursions seen 2 days ago,
and from these data alone one would judge that the empirical correction
is performing adequately.
Ho hum.
Iain Coulson
Latest Update : 22 Mar 2001
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