When we look at the light curve for an eclipsing binary system with
total eclipses, how can we tell which star is hotter?

"The analysis of the minimum of the light curve corresponding to the
primary eclipse would yield several important parameters. We obtained
the distance d to the binary system. Then the ratio of the relative
depths of the minima (in terms of the apparent visual magnitudes mv)
gives us the ratio of the absolute visual magnitudes Mv through the
modulus equation:

Mv= mv - 5log10d - 5 + A

The ratio of the absolute visual magnitudes then gives a ratio of
luminosities if we use the relation:

M = Msun - 2.5 log10(L/Lsun)

Finally this, with the Stefan Boltzman law:

L = 4 pi sigma r^2 T^4


gives a ratio of the temperatures

(Tl/Ts)^4

where Tl is the effective temperature of the larger companion and Ts
that of the smaller."

http://www.macalester.edu/astronomy/research/phys40/momar/webpage.html
"A study of eclipsing binary systems." by Momar Dieng

sincerely,

Wonko

Terrific!