The cluster ages experiment (CASE). VII. Analysis of two eclipsing binaries in the globular cluster NGC 6362

Abstract

We use photometric and spectroscopic observations of the detached eclipsing binaries V40 and V41 in the globular cluster NGC 6362 to derive masses, radii, and luminosities of the component stars. The orbital periods of these systems are 5.30 and 17.89 d, respectively. The measured masses of the primary and secondary components ($M_p$, $M_s$) are (0.8337$\pm$0.0063, 0.7947$\pm$0.0048) M${}_{\odot }$ for V40 and (0.8215$\pm$0.0058, 0.7280$\pm$0.0047) M${}_{\odot }$ for V41. The measured radii ($R_p$, $R_s$) are (1.3253$\pm$0.0075, 0.997$\pm$0.013) R${}_{\odot }$ for V40 and (1.0739$\pm$0.0048, 0.7307$\pm$0.0046) R${}_{\odot }$ for V41. Based on the derived luminosities, we find that the distance modulus of the cluster is 14.74$\pm$0.04 mag -- in good agreement with 14.72 mag obtained from CMD fitting. We compare the absolute parameters of component stars with theoretical isochrones in mass-radius and mass-luminosity diagrams. For assumed abundances [Fe/H] = -1.07, [$\alpha$/Fe] = 0.4, and Y = 0.25 we find the most probable age of V40 to be 11.7$\pm$0.2 Gyr, compatible with the age of the cluster derived from CMD fitting (12.5$\pm$0.5 Gyr). V41 seems to be markedly younger than V40. If independently confirmed, this result will suggest that V41 belongs to the younger of the two stellar populations recently discovered in NGC 6362. The orbits of both systems are eccentric. Given the orbital period and age of V40, its orbit should have been tidally circularized some $\sim$7 Gyr ago. The observed eccentricity is most likely the result of a relatively recent close stellar encounter.

Accepted by AJ

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