| Abstract
| - We consider the formation and migration of protoplanetary embryos in discs around the stars in tight binary systems (separations of ∼20 au). In such systems, the initial stages of runaway embryo formation are expected to only take place within some critical disc radius acrit, due to the perturbing effect of the binary companions. We perform N-body simulations of the evolution of such a population of inner-disc embryos surrounded by an outer disc of smaller planetesimals. Taking Alpha Centauri-B as our fiducial reference example in which acrit∼ 0.7 au, and using a Minimum Mass Nebular Model with Σ∝a−3/2, we find that within 106 yr (107 yr), systems will on average contain embryos which have migrated out to 0.9 au (1.2 au), with the average outermost body having a mass of 0.2 M⊕(0.4 M⊕). 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 the semimajor axis of the outermost embryo in these simulations is found to be essentially independent of acrit, and we note that little further embryo migration takes place beyond 107 yr. We conclude that the suppression of runaway growth outside acrit does not mean that the habitable zones in such tight binary systems will be devoid of detectable, terrestrial mass planets, even if acrit lies significantly interior to the inner edge of the habitable zone.
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