[Aavso-photometry] B-V from V-I

[Arne Henden]

There are differences between colors of giants and dwarfs, but
primarily at the cool end.  The giants have lower gravity and need
lower temperature to match the same spectral type of dwarfs,
so the colors of "cool" (say, G/K) giants are typically redder.
Arne

Michael Koppelman wrote:
> Great, thank you.
> 
> An implicit question hidden in my question was: should this really 
> depend on what kind of star it is? Do we start getting complications 
> from emission and absorption on some stars or something? Seems like a 
> blackbody should pretty well approximate most stars when talking about 
> these fairly large bandpasses.
> 
> Thanks!
> 
> Cheers,
> Michael Koppelman
> http://www.lolife.com/astronomy/
> 
> On Feb 20, 2005, at 11:19 AM, Arne Henden wrote:
> 
>> For dwarfs, the relation is approximately
>> (B-V) = -0.07 + 0.88*(V-I)
>>
>> In other words, (B-V) is usually slightly smaller than (V-I).
> 
> 
> 
>