EFFECT OF INTRUDER MASS ON COLLISIONS WITH HARD BINARIES .2. DEPENDENCE ON IMPACT PARAMETER AND COMPUTATIONS OF THE INTERACTION CROSS-SECTIONS

I simulated over 125 000 encounters between a hard binary (orbital velocity is 10(3) times the impact velocity) with equal mass M0, components and orbital eccentricity e(o) = 0 and intruders with masses ranging from M(i) = (0.01 to 10 000) M0. Each encounter was followed up to a maximum of 5 X 10(6) integration steps to allow long-term "resonances," temporary trinary systems, to break into a binary and a single star. These simulations were done over a range of impact parameters to find the cross sections for various processes occurring in these encounters. Many cross sections, particularly that for energy exchange, tend to approach simple analytic limits if M(i)/M0 much less than 1 and M(i)/M0 much greater than 1. The cross sections tend to have inflection points around M0/M0 = 1 that cannot be modeled except by detailed numerical simulations. A critical impact parameter found in these simulations is the one beyond which no exchange collisions can occur. The closest approach distance, R(min), corresponding to this impact parameter is R(c) congruent to 2.1 a(o)[(M(i) + 2M0)/2M0]1/3 where a(o) is the initial semimajor axis of the orbit. The energy exchange between the binary and a massive intruder decreases greatly in collisions with R(min) greater-than-or-equal-to R(c). The semimajor axes and orbital eccentricity of the surviving binary also drops rapidly at R(c) in encounters with massive intruders. The formation of temporary trinary systems is important for all intruder masses. There is a drastic increase ("rupture") in the median semimajor axis, [a(out)], of the outer member of the trinaries (resonances) formed in encounters where R(min) greater-than-or-equal-to R(c); i.e., [a(out)] typically increases by a factor of 10(4) in going from R(min) = R(c) to 1.5R(c). These trinaries have long lives, so they have a chance of being stabilized by the perturbations of other stars that can decrease the eccentricity of the outer member of the trinary sufficiently that it no longer passes near the inner binary. This can produce stable trinaries with very distant members such as Proxima Centauri orbiting the Alpha Centauri binary.