[vsnet-chat 5676] Re: B-V question

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

     You can get fairly good V-R from B-V for stars of ordinary color.
A pretty good transformation is:  V-R = 0.508(B-V) = 0.040   which is
very good in the range 0.3 < B-V < 0.9, and goodo enough bluer than this,
and out to about B-V = 1.2.

>>  should I use Guide 7 magnitudes or is it better to use the values
>>  that Simbad returns.

     If the SIMBAD values are from "real" photoelectric or CCD
photometry, then this will generally be preferable.

>>  differential photometry of a eclipsing binary in V, R, and I...

     One might ask _why_ all three colors rather than just, say, V and I
or V and R.  If it's to get some temperature information about the
components of the binary, then using V-I will give you the best baseline
(and R or V-R will be superfluous).
     Is there previous photometry of the binary you are interested in?
If so, it could be that someone has calibrated some nearby comparison
stars.  Also, have a look at this big photometric reference file:

http://ftp.lowell.edu/pub/bas/starcats/loneos.phot

...to see if there happen to be some stars near your target.
     Hope this helps.

\Brian

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