2007A&A...461.1065C

In order to increase the limited number of B-stars with accurately known dimensions, and also the number of well studied eclipsing binaries in open clusters, we have undertaken observations and studies of four southern double-lined eclipsing B-type binaries; DW Car, BF Cen, AC Vel, and NSV 5783. Complete uvby light curves were observed between January 1982 and April 1991 at the Danish 0.5m telescope at ESO La Silla, since 1985 known as the Stroemgren Automatic Telescope (SAT). Standard indices for the systems and the comparison stars, as well as additional minima observations for AC Vel, have been obtained later at SAT. For DW Car and AC Vel, high-resolution spectra for definitive spectroscopic orbits have also been obtained; they are presented as part of the detailed analyses of these systems. A few spectra of NSV 5783 are included in the present paper. For all four systems, the first modern accurate light curves have been established. DW Car is a detached system consisting of two nearly identical components. It is member of the young open cluster Cr228. A detailed analysis, based on the new light curves and 29 high-resolution spectra, is published separately. BF Cen is semidetached and is member of NGC 3766. Modern spectra are needed for a detailed study. AC Vel is a detached system with at least one more star. A full analysis, based on the new light curves and 18 high-resolution spectra, is published separately. NSV 5783 is discovered to be an eclipsing binary consisting of two well-detached components in an 11-day period eccentric (e=0.18) orbit. Secondary eclipse is practically total. From the light curves and a few high-resolution spectra, accurate photometric elements and preliminary absolute dimensions have been determined. The quite similar components have masses of about 5M_☉ and radii of about 3.5R_☉, and they seem to have evolved just slightly off the ZAMS. The measured rotational velocities (≃150km/s) are about 6 times those corresponding to pseudosynchronization.