Total brightness of a binary star system.

Steve Willner wrote:
In article .com,
"sed" writes:
Does anyone know how to calculate a total brightness of a binary system
if brightness of each individual start and their radial separation is
known?


(cut)
" Starlist 2000" by Richard Dibon-Smith, gives the formula,
Combined magnitued of binary stars M1 and M2
= Mcombined = M2 - 2.5*[inv log .4(M2-M1) +1]

- A. McIntire