**2.3.4. Detached Eclipsing Binaries**

Detached double-spectroscopic eclipsing binaries provide us with a unique
chance to obtain the distance in a semi-geometric way out to LMC or even
farther.
From the information given by the light curve and velocity curve,
one can solve for the orbital parameters and stellar radii
(Andersen 1991,
Paczynski 1997;
Bell et al. 1993
for an earlier application to LMC HV2226;
Torres et al. 1997
for an application to the Hyades). If surface brightness
of the two stars is known from colour or spectrum, one can obtain the
distance as *d* = (*F/f*)^{1/2}*R*_{i}
where *F* and *f* are fluxes at the source and
the observer and *R*_{i} is stellar radius.
Guinan et al. (1998)
applied this method to HV2274 in LMC
and derived *m - M* = 18.30 ± 0.07 with the aid of Kurucz'
model atmosphere
to estimate surface brightness from the spectrum.
Udalski et
al. (1998b)
claimed that the extinction used
is too small by an amount of
*E(B - V)* = 0.037 mag
based on OGLE
multicolour photometry. If we accept this correction the distance becomes
0.11 mag shorter, i.e., *m - M* = 18.19.