Re: NSV 10892 Photometry

[aah@nofs.navy.mil]

>One other question I have: if you take your V observation, then 
>you switch filters, re-focus and take your B observation, the 
>star may have changed by a substantial amount. It changes by 
>0.16 mag/hour between a given max and min, or 0.03 mag in about 
>10 minutes. Can't that screw up B-V sorts of measurements?
  For the record, my BVRI dataset was taken over an interval of
about 4 minutes (counting readout time and filter changes).
The individual exposures were in the 3-7 second range (this is a
very bright star for me).  If the star were an EW, changing
its brightness constantly, then long delays between filters
would add error.  In those cases, your best techniques are
to only observe where things are not changing rapidly (such
as at the maxima), or to observe one night in one color, and
the next night in another color, and interpolate on the
phased light curves to get the star color.  (Or use a TASS system!)
  Usually (V-I) ~ 1.1 * (B-V) for normal stars.
Arne