[Aavso-photometry] which stars? which band?

[arne]

Yenal Ogmen wrote:
> Hi all,
> 
> Last night, for the first time, I tried B and R bands
> for various stars. When I got results, I checked the
> other observations from other observers but didnt find
> any other observations on other bands (other than V).
> How shall I know which stars need to be observed on
> other bands too?
> 
Multifilter observations are still in their infancy as far as
most amateurs are concerned.  We recommend V-band measures
for first-time CCD observers, and many people are satisfied
with that and don't progress any further.

Multifilter observations are a "poor man's spectroscopy", as they
are just broadband measures of the star spectrum.  Therefore,
whenever you expect something to be different at one wavelength
than another, multifilter observations will be valuable.  That
occurs with almost everything!  For CVs, the color of the system
is different in outburst than at quiescence; you may detect the
donor star at red wavelengths, but not in the blue; magnetic stars
will show a cyclotron hump at Rc but not at other bandpasses; etc.
Pulsating stars change color as they change temperature during
their pulsational cycle; eclipsing binaries change color as one
star or the other is eclipsed.  Those that change color are
obvious candidates for transformation, which requires at least
two filters.

Now that decent photometry is becoming available for every AAVSO
program star field, feel free to experiment with other bandpasses than
just Johnson V and see what you get.  As for what star needs to
be observed at B or Rc - I'd look at the pulsating stars first,
such as Miras, Cepheids or RR Lyrs.  If you have enough signal,
I'd pick B first, as the (B-V) color generally tells you more
than the (V-Rc) color does.
Arne