Abstract
The spectroscopic binary CPD -59°2628 (Sp = O9.5 V) has been discovered to be a detached eclipsing binary, and we present an analysis based on new light curves, published spectroscopy and two new high-resolution spectra. uvby light curves from more than 2000 observations are analysed with the WINK and the Wilson-Devinney (WD) programs. Geometric distortions and photometric effects from the proximity of the components are included in the computations. The detached system has a close circular orbit of high inclination and high maximum projected velocities. We find a photometric period P=1fd47 which is consistent with the spectroscopy-binary period by Solivella & Niemela (\cite{solivella&niemela99}). We use this period to rematch the misidentified radial velocities from Levato et al. (\cite{levato&al91}) and apply them in an analysis using the method of Lehmann-Filhes. We find that CPD -59°2628 is a young system close to the ZAMS. Its distance is 2.6+/-0.1 kpc and it has a systemic velocity of -19 km s^{-1}, confirming its membership in the cluster Trumpler 16 (radial velocity -23.5 km s^{-1}). The temperatures are 32 000 K for the hotter star (A) and 30 000 K for the cooler (B). We determine the absolute dimensions (solar units): M_A=14.0+/-2.0, R_A=5.29+/-0.26, M_B=11.7+/-1.8 and R_B=4.38+/-0.22. By adopting E(b-y)=0.306, we get M_{bol,A}=-6.3+/-0.1, M_{V,A}=-3.2+/-0.1, M_{bol,B}=-5.6+/-0.1 and M_{V,B}=-2.7+/-0.1. Theoretical stellar models from Claret (\cite{claret95}), including convective-core overshooting and mass loss for a composition (X=0.70, Z=0.02), appear to fit the components at an age of ~ 2 Myr. Based on observations obtained at the European Southern Observatory at La Silla, Chile (Applications 62H-0110, 62H-0110 and 64.L-0031) and the South African Astronomical Observatory, Sutherland, South Africa.