I forgot to mention…Stars in a binary system do not necessarily have the same mass, size or brightness. In a certain binary-star system, each star has the same mass which is 2.4 times of that of the Sun, and they revolve about their center of mass. A star's mass will vary over its lifetime as mass is lost with the stellar wind or ejected via pulsational behavior, or if additional mass is accreted. In other words, stars themselves set their own masses. This helps explain why stars formed in disparate environments still have similar masses! But anyways, enjoy your time!