[Aavso-photometry] BVRI Observing Program

[arne]

Keith Graham wrote:
> I was wondering if the BVRI Photometry Observing Program is still in operation. If so, are there new charts for those stars in the program? I see that the photometry charts for these stars in VSP does not include Rc and Ic mags. I also see some changes in the V mags in the updated charts.
> 
Good question.
There are some holes in the current VSP/VSD update.  First, all stars
with magnitudes more than 0.2mag different than their old chart values
were not uploaded.  Second, all CCD charts, BVRI photometry charts, etc.
had photometry listed on them that did not get copied into VSD.  This
will happen during the January load.

The CCD BVRI program picked 8 stars to follow: S Per, U Ori, VX Gem,
DH Dra, VX UMa, W Leo, RU Vir, and RR Boo.  Many of the comp stars
were bright (some of these are bright Miras, after all), and those
were filled in using Tycho2 values during this initial load of the
comp star database.  I'd recommend using the original BVRI charts
and not VSP for these 8 stars until we properly populate the database.

On the other hand, a couple of those fields were observed by me for
other reasons.  An example is VX Gem.  It is interesting to compare
my 3-night BVRI calibration at Sonoita with the calibration on the
BVRI chart:

91, 94 101 and 104 are saturated at SRO, as our goal was accurate
photometry from 11-15mag

ID     B       V      Rc      Ic
110  12.035  10.990  10.440   9.940 SRO
      12.043  11.017  10.466   9.956 CCD

115  12.172  11.509  11.134  10.780 SRO
      12.155  11.509  11.138  10.776 CCD

122  12.899  12.219  11.848  11.516 SRO
      12.893  12.235  11.867  11.503 CCD

127  13.266  12.715  12.384  12.079 SRO
      13.284  12.746  12.412  12.095 CCD

128  13.898  12.826  12.257  11.735 SRO
      13.928  12.859  12.284  11.669 CCD

139  14.428  13.940  13.624  13.324 SRO
      14.478  13.989  13.673  13.196 CCD

You can see that, in general, the agreement is quite good.  As the
stars get fainter, there appears to be a systematic offset for BVR,
and a very obvious difference at Ic.  Who is right?  You might observe
yourself and see which set of magnitudes comes closest to your own
transformed values, using perhaps the 115 star as the zeropoint.
I'd like to hear your answers!  The Howell, Mattei and Benson paper
(1993, JAAVSO 22, 2) indicated that they had two clear nights and
two partly cloudy nights, and that they covered 19 fields (of which
8 were used to create the BVRI program).  I don't know if the other
11 were finally processed.  They indicate that they did 3 measures
on one night for each of the fields, and did not give the standard
deviation of the measures in the paper.
Arne