2007AJ....133.2457K

We use photometric and spectroscopic observations of the detached eclipsing binary V209 ω Cen to derive the masses, radii, and luminosities of the component stars. The system exhibits total eclipses and, based on the measured systemic velocity and the derived distance, is a member of the globular cluster ω Cen. We obtain 0.945±0.043 M_☉, 0.983±0.015 R_☉, and 6.68±0.88 L_☉ for the cooler but larger and more luminous primary component. The secondary component has 0.144±0.008 M_☉, 0.425±0.008 R_☉, and 2.26±0.28 L_☉. The effective temperatures are estimated at 9370 K for the primary and at 10,866 K for the secondary. On the color-magnitude diagram of the cluster, the primary component occupies a position between the tip of the blue straggler region and the extended horizontal branch, while the secondary component is located close to the red border of the area occupied by hot subdwarfs. However, its radius is too large and its effective temperature is too low for it to be an sdB star. We propose a scenario leading to the formation of a system with such unusual properties, with the primary component ``reborn'' from a former white dwarf that accreted a new envelope through mass transfer from its companion. The secondary star has lost most of its envelope while starting its ascent onto the subgiant branch. It failed to ignite helium in its core and is currently powered by a hydrogen-burning shell.