Monthly report for August 2001 by Christian A. Hummel:

Hummel reanalysed the astrometric data taken on 1999-03-06 
when the feed direction was centered on the siderostat. 
(The feed direction is usually offset from the center to
avoid obscuration by the cats-eye.) He showed that with 
metrology correction and using the improved dispersion
correction code, the residual delay RMS could be reduced to
2.5 microns. This is markedly better than in nights with 
off-center feed and is evidence for the systematic errors
caused by this alignment if left uncorrected.

Hummel worked on the analysis of the siderostat motor angle
data and pointing models to investigate the possibility of 
correcting off-center feed observations using the derived
precise mirror orientations. In the course of this, he
identified and measured the periodic errors in the siderostat
drives.

Hummel prepared material for a session he is moderating
at the IAU working group meeting on optical interferometry
in France, the last two days of August. This session is on
common software development. Other sessions include the
adoption of a common data format for optical interferometry,
imaging algorithms, and long term plans.