[Aavso-photometry] U Gem R and I

[arne]

Walt Cooney wrote:
> I got an hour and a half run on U Gem last night mostly in V but with B, R, and
> I interspersed.  I can reduce and submit the B and V data with the sequence on
> the AAVSO web site.  Are there any recommendations for comp star magnitudes in R
> and I?
> 
Brian Skiff has obtained R,I magnitudes for a few stars in the
field of U Gem from the literature; do a VizieR search of the U Gem field
and find his UBVRI photometry of faint field stars catalog
(II/277/loneos).

SDSS covers this field; you can also get BVRI transformations of
their ugriz photometry, but only for stars fainter than 14th.
See Ivezic et al. 2007, astro-ph/073157 for the transformation
equations.

I also have been meaning to create a V-r' transformation, which
could then make use of the Henden BV calibration of this field
along with the CMC14 r' photometry of the field to derive Rc,Ic
magnitudes.  Haven't done it yet.

TASS has covered this field; again, you can obtain the data through
VizieR.  That gives you rough estimates of Ic for the field stars.

Finally, for input to the AAVSO, you can just guestimate the magnitude
of any comp star, use that guess and submit.  Put the chosen magnitude
in the comment field so that the data can be corrected later.  Good
guesses are
(V-Rc) = 0.5 (B-V)
(V-Ic) = 1.1 (B-V)

Many of my NOFS calibrations were just B and V, as their intent was
to improve visual sequences on charts and were done as a back-burner
project to help the AAVSO.  Since then, CCD photometry has become
more prevalent and red calibrations are commonly requested.  At SRO,
we are doing BVRI calibrations routinely, but the older fields still
suffer.
Arne