Circularization in B-type eclipsing binaries in the Magellanic Clouds

Making use of detached eclipsing binaries discovered by the OGLE and MACHO teams in the SMC and in the LMC respectively, we give the value of the fractional radius above which circularization occurs. We show that this critical radius is consistent with that found for galactic binaries by Giuricin et al. (1984) and does not, therefore, depend strongly on metallicity. This conclusion is consistent with Zahnʹs (1975) theory of tidal dissipation. The critical radius seems slightly larger in the SMC than in the LMC, but this small difference is hardly significant and should be confirmed by a larger sample. We also explore empirically to what extent the critical radius might depend on stellar mass and surface gravity.