  We consider the formation and migration of protoplanetary embryos in disks
around the stars in tight binary systems (separations ~ 20 AU. In such systems,
the initial stages of runaway embryo formation are expected to only take place
within some critical disk radius a_{crit}, due to the perturbing effect of the
binary companions (Thebault et al. 2009). We perform n-body simulations of the
evolution of such a population of inner-disk embryos surrounded by an
outer-disk of smaller planetesimals. Taking Alpha Centauri-B as our fiducial
reference example in which a_{crit} ~ 0.7 AU, and using a Minimum Mass Nebular
Model with $\Sigma \propto a^{-3/2}$, we find that within 10^6 yrs (10^7 yrs),
systems will on average contain embryos which have migrated out to 0.9 AU (1.2
AU), with the average outer-most body having a mass of 0.2 M_{earth} 0.4
M_{earth}. Changes to increase the surface density of solids or to use a
flatter profile both produce increased embryo migration and growth. At a given
time, the relative change in semi-major axis of the outer-most embryo in these
simulations is found to be essentially independent of a_{crit}, and we note
that little further embryo migration takes place beyond 10^7 years. We conclude
that the suppression of runaway growth outside a_{crit} does not mean that the
habitable zones in such tight binary systems will be devoid of detectable,
terrestrial mass planets, even if a_{crit} lies significantly interior to the
inner edge of the habitable zone.
