[vsnet-chat 5528] Re: BVRI

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

     Stan scriveth:

>>  ...but - how do you recognise likely
>>  variable stars in this sytem without the U and with I perhaps not as 
>>  good as
>>  it should be...

     Not sure I follow you here:  in most cases, variability will show
up quite similarly in all filters.  Do you mean how do you recognize
the type of variable star using colors that don't include the U band?

>>  Also, is there any way of determining reddening, etc., using
>>  these filters?

     Well, sorta.  The problem is that the reddening lines in BVRI are
nearly parallel to the color trends, though between mid-F and K types
you can get good reddening if you have high-precision BVI colors.
See Pollacco & Ramsay (1992 MNRAS, 254,228) for application details.

>>  We can probably forget the B as this is useful only in
>>  measuring Cepheids...

     Colors involving the B filter can be useful for just about any
sort of star.  It does turn out that V-I is a more sensitive indicator
of temperature than B-V, particularly for cool stars, but B-V is
just fine for anything hotter.
     For most sorts of variable-star observing, just getting V and some
other color (like B-V, V-R, or V-I) is entirely sufficient.  My opinion
is that this business of trying to get all UBVRI filters is a waste
of effort unless there is good astrophysical reason to do so for a
specific target.

\Brian

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