ECLIPSING BINARIES IN THE MAGELLANIC CLOUDS .1. ABSOLUTE DIMENSIONS AND DISTANCE MODULUS FOR HV-2226 IN THE SMALL MAGELLANIC CLOUD

Absolute dimensions and the distance modulus have been established for the early-type eclipsing binary HV 2226 in the SMC. Analyses of the new radial velocities reported here, and CCD light curves published by Jensen et al., yield component masses of 9.3 +/- 0.7 and 5.6 +/- 0.5 M., respectively. The radii are 5.6 +/- 0.2 and 5.3 +/- 0.2 R. with the secondary component filling its Roche lobe which implies that HV 2226 must have evolved through a case A mass-transfer process. More radial-velocity data are needed for definitive orbital parameters of HV 2226, and new 5-15 M. evolutionary models at reduced metallicities are needed for detailed studies of SMC and LMC binaries in general. A distance modulus of (m(V)-M(V))O = 18.6 +/- 0.3 mag is derived, marginally lower than the adopted mean of 18.9 mag for the SMC. The position of HV 2226, however, indicates that it is in fact situated in the near side of the SMC. In the present case, the accuracy of this estimate is limited mainly by the uncertainties of almost-equal-to 2000 K in the effective temperatures. We point out that distance moduli with uncertainties of +/- 0.15 mag can be achieved from accurate radial velocities, light curves and colour indices of eclipsing binaries; such systems in the SMC and LMC are therefore promising distance indicators and work on further selected candidates is in progress.