Photometry with AIP4Win 2

Community
1

Good morning friends.
I would like to submit a question: I use AIP4Win 2 to do multicolor aperture differential photometry (B, V, Rc, Ic) of variable stars.
The output text file shows, in addition to the time values, the Var-Com (V-C) and the Chk-Com (K-C) values in each color with relative error bars.
The question is following: having the magnitudes of the comparison (C) and of the check (K) in the BVRcIc standard and having the instrumental transformation coefficients, is it possible, and if so, with which formulas, to obtain the trasformed magnitudes of the variable (V) in B, V, Rc and Ic?
Thanks in advance to all those who can help me.

Massimiliano Martignoni
Milan, IT

2

Here are the formulae I use for B and V filters. Those for other filter pairs can be obtained by substitution.

(B-V)var = (B-V)comp +Tbv[(b-v)var – (b-v)comp]
Vvar = Vcomp + vvar – vcomp +Tv_bv[(B-V)var – (B-V)comp]

B-V is the calculated transformed colour index, or catalogue colour index
V is the calculated transformed or catalogue V magnitude
b-v is the instrumental BV colour index
v is the instrumental V magnitude
var is the variable
comp is the comparison star
Tbv is the transformation coefficient obtained by plotting b-v (y axis) against B-V (x axis). The coefficient is the reciprocal of the slope.
Tv_bv is the transformation coefficient obtained by plotting V-v (y axis) against B-V (x axis). The coefficient is the slope.

For the check star, simply substitute check for var.

I’m not sure how many people know this, but these formulae can be derived algebraically from those that describe the transformation plots.

Roy