  We used the database of eclipsing binaries detected by the OGLE microlensing
project in the pencil-beam search volume toward Baade's Window to define a
sample of 74 detached, equal-mass, main-sequence binary stars with short
orbital periods in the range 0.19<P<8 days. The logarithmic slope of the period
distribution, logN propto (-0.8 pm 0.2) logP, was used to infer the
angular-momentum-loss (AML) efficiency for the late, rapidly-rotating members
of close binaries. It is very likely that the main cause of the negative slope
is a discovery selection bias that progressively increases with the orbital
period length. Assuming a power-law dependence for the correction for the bias:
bias propto -C logP (with C ge 0), the AML braking-efficiency exponent alpha in
dH/dt = P^-alpha can take any value alpha = (-1.1 pm 0.2) + C. Very simple
considerations of discovery biases suggest C simeq 4/3, which would give an AML
braking law very close to the "saturated" one, with no dependence on the
period. However, except for plausibility arguments, we have no firm data to
support this estimate of C, so that alpha remains poorly constrained. The
results signal the utmost importance of the detection bias evaluation for
variable star databases used in analyses similar to the one presented in this
study.
