THE ORBITAL ECCENTRICITIES OF BINARY MILLISECOND PULSARS IN GLOBULAR-CLUSTERS

Low-mass binary millisecond pulsars (LMBPs) are born with very small orbital eccentricities, typically of order e(i) similar to 10(-6)-10(-3). In globular clusters, however, higher eccentricities e(f) much greater than e(i) interactions with passing stars. Here we show that the cross section for this process is much larger than previously estimated. This is because, even for initially circular binaries, the induced eccentricity e(f) for an encounter with pericenter separation r(p), beyond a few times the binary semimajor axis a declines only as a power law, e(f) proportional to (r(p)/a)(-5/2), and not as an exponential. We find that all currently known LMBPs in dusters were probably affected by interactions, with their current eccentricities typically greater than at birth by an order of magnitude or more.