Visibilities larger than unity
If the data reduction returns visibilities grater than unity, it could
be related to a chopping problem during the photometry. Check the
ESO HIERARCH ISS CHOP THROW keyword, which, when set to zero,
indicates a problem with chopping. (This does not necessarily
mean that the template contained
a value of zero for the chopping throw.) This reduces the flux in the
chopped spectrum and consequently leads to a normalization of the fringe spectrum
with a flux too small, causing larger than real visibilities.
Christian A. Hummel
European Southern Observatory
Casilla 19001
Santiago 19
Chile
