[Aavso-photometry] Multi-color photometry

[Michael Koppelman]

Yes, you can do this. Usually, though, you'll have the best S/N in  
certain bandpasses and should just use those. For my system, for  
example, I don't use B-V to determine V, I use V-R or V-I because my  
B data is always worse. I could get V from both and average them.

Michael


On Nov 3, 2005, at 3:37 AM, Brian C. Barnes wrote:

> 1) Assume I have B, V, and R filtered images of M67 along with B,  
> V, and R
> images of a target. I can create transformation coefficients for B- 
> V, and
> using those, I can calculate B and V. I can also create a  
> transformation
> coefficient for V-R, and I can then calculate R by calculating V-R  
> and using
> the V value from the B-V calculation, or I can calculate V-R and  
> then V and
> R individually just like I did with B and V. This would give me one  
> B value,
> 2 V values, and 1 R value. I can then average the 2 V values to get  
> a final
> V value. Is there an advantage to calculating this extra V value  
> and doing
> the averaging?
>
> 2) Extending question one somewhat, if there is an advantage to  
> having 2 V
> values and averaging them, then it would seem that having extra B  
> and R
> values would also be a good thing. This is easily done by creating
> transformation coefficients for B-R, and calculating separate B and  
> R values
> from these. I would then end up with 2 B values, 2 V values, and 2  
> R values,
> which would each be averaged. Is this a valid thing to do? And if  
> so, would
> it also be valid to have transformation coefficients for the other  
> possible
> combinations of UBVRI? (i.e. U-V, U-R, U-I, B-R, B-I, and V-I)
>
> Obviously, this is a lot of number crunching, but automating it all  
> in a
> spreadsheet would be simple enough. I just don't know if I would  
> get better
> numbers, or worse numbers, doing this.