Re: Re: USNO A2.0 "R"

[aah@nofs.navy.mil]

My conversion tables for USNO-A gave transformations
between any combination of BVRI and OEJFN.  Dave Monet
used primarily Tycho2 for setting the zeropoint of each
plate since there were sufficient Tycho2 stars to cover
the spatial extent.  However, these tables with fainter
stars can also be used for removing the nonlinearity of
the photographic process.  I don't think that was done,
but we did it for USNO-UJ.
  Regarding what USNO-A "R" refers to, it is the native
E-plate magnitudes, but zeropointed on the Cousins Rc system.
So there is a rough correspondence with Cousins Rc, especially
for the modal color, but there will be large errors at
extreme colors.
Arne