calibrating Mark IV data

[Stupendous Man <richmond@a188-l009.rit.edu>]

  Tom Droege asked about the Mark IV:

> My guess is that we will have a 5
> mag range between noise and saturation.  If I am correct (from star counts)
> that we can measure mag 15, then we saturate at 10.   This means that we
> will need a catalog of mag 11 or so stars for calibration.  
> Is this available?

  [brief answer: yes]

  Brian Skiff has been steadily scouring the astronomical literature
to compile a set of stars with "reasonable" measurements of magnitude:
not good to 1%, but perhaps good at the 5% to 10% level.  I've been
placing slightly re-formatted copies of his compilations on the 
TASS "Stellar Catalogs" page.  See

         http://a188-L009.rit.edu/tass/catalogs/catalogs.html#loneos

  The catalog has about 22,000 stars at the moment, scattered all over
the sky.  Most of these have only B and V magnitudes, but there are
about 3600 with V-band and I-band measurements.  We will probably 
catch 3-5 stars with V-band measurements in each Mark IV image;
some Mark IV fields will contain no stars with I-band measurements,
but I suspect that about 1 in 5 fields will contain several I-band
standards.

  I think we can do a good job of calibrating the data to the level
of 10% with this catalog, right away.  We could probably go back
later and re-calibrate the data to a higher degree of accuracy
if we wished.

  If Arne puts the first Mark IV into action, I would not be surprised
to see him command it to take pictures of some _real_ standard stars
(such as those in the Landolt catalogs) very frequently -- say,
once or twice per hour.  He could probably tell us a lot about
the photometric transformations necessary to place (his) Mark IV
data onto the standard Johnson-Cousins magnitude scale.

                                    Michael Richmond