[vsnet-chat 5557] Re: [AAVSO-DIS] Re: The curious case of BD+59 224

[Brian Skiff <Brian.Skiff@lowell.edu>]

     I appreciate Doug's eeforts in getting the U-B color
for BD+59 224---to the extent of getting a U filter for his camera.
Although the numbers aren't definitive yet, I think this does point to the
star being a close binary with both a very hot and a cool component
like VV Cep or zeta Aur (without the eclipses).  Actually, there isn't
enough study to rule out the eclipses, which might be years apart.
     For Stan:  I tend to associate "blue" U-B colors in M-type stars with the
emission features seen in Miras, and thus would discount it in this
case because there is no evidence that the star is substantially
variable in the BD or any later astrometric catalogue.  The Tycho-2 
photometry errors are about what's expected for a star of this brightness.
This doesn't exclude small-amplitude variations of a couple tenths of
a magnitude or less, and I would expect something like this for this star.
     I don't quite know what Doug is doing in re his reductions, but
the description gives me the impression that he isn't taking into account
color terms in his system, and this is producing the wide dispersion of
results when he compares against different stars.  My recommendation
to Doug would be to spend the time on three or four stable "photometric"
nights to hit a couple dozen bona-fide standard stars/fields to determine
color coefficients for his system.  Assuming these yield consistent results,
simply _assume_ that they are stable thereafter (check them a couple times
per year on good nights).  Then when observing a field with just one or
two comparison stars with "known" values, you can get reasonably good
results from the colors of those stars because you have the color terms
pretty well nailed independently.  You don't have to rely on data taken
just from that current night to determine them.

\Brian

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