[vsnet-chat 743] Re: CHAT - Relation between I-V and/or R-V magnitudes?

[aah@nofs.navy.mil]

Robert Fidrich asked,
>...Could you give something figures what is the relation between
>I-V, R-V magnitudes?
  The FASTT variables are only listed with R magnitudes since the telescope
is a transit instrument with a single CCD and can only get one 'image' of
each field per night.  We picked R because that was the maximum sensitivity
of the CCD; other sites probably had similar reasons.
  The usual rule of thumb is that (B-V) = (V-I), and (V-R) = (R-I).  This means
that, for most objects, they will be 'brighter' at R and I than they are at V.
The USNO-A catalog reports R-like magnitudes for all of its stars and can be
used to set up a rough sequence.
Arne
--------------------------------------------------------------------
Arne Henden                               Instruments/software/CCDs
US Naval Observatory Flagstaff Station    Cepheids/photometry/IR
P.O. Box 1149                             http: ftp.nofs.navy.mil  
Flagstaff, AZ 86002-1149                  Voice: (520)779-5132
aah@nofs.navy.mil                         FAX:   (520)774-3626

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