Eclipsing binaries in the open cluster NGC 2243 - II. Absolute properties of NV CMa.pdf

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Eclipsing binaries in the open cluster NGC 2243 - II. Absolute properties of NV CMa.pdf

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Eclipsing binaries in the open cluster NGC 2243 - II. Absolute properties of NV CMa

a r X i v : a s t r o - p h / 0 6 0 9 3 8 0 v 1 1 4 S e p 2 0 0 6 1 Eclipsing binaries in the open cluster NGC 2243 - II. Absolute properties of NV CMa ? J. K a l u z n y1, W. P y c h1 , S. M. Rucinski2 and I. B. T h o m p s o n3 1Nicolaus Copernicus Astronomical Center, ul. Bartycka 18, 00-716 Warsaw, Poland e-mail: (jka,pych@.pl) 2David Dunlap Observatory, Department of Astronomy and Astrophysics, University of Toronto, P.O. Box 360, Richmond Hill, ON L4C 4Y6, Canada e-mail: (rucinski@astro.utoronto.ca) 3Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101, USA e-mail: (ian@) ABSTRACT We present echelle spectroscopic data for five eclipsing binary stars and two giant stars in the field of the open cluster NGC 2243. The average cluster velocity is determined to be +60.4±0.6 km s?1. Four of the eclipsing binaries are very likely members of the cluster based on their observed radial velocities. The absolute parameters of cluster member NV CMa are determined by analysing photometric and radial velocity data. We obtain 1.089±0.010M⊙ and 1.221±0.031R⊙ for the primary, and 1.069±0.010M⊙ and 1.178±0.037R⊙ for the secondary. Both components of the binary are located on the Main Sequence, about 1 mag. below the turn-off point on the cluster color-magnitude diagram. Using model age-luminosity and age- radius relations we obtain 4.35±0.25 Gyr for the age of NV CMa. The derived age is, however, very sensitive to the adopted metallicity of the cluster. We demonstrate that a meaningful determination of the ages of objects like NV CMa based on evolutionary models is possible only if their metallicity is know with a relative accuracy of a few percent. The distance moduli calculated for the components of NV CMa agree closely with each other, and imply an apparent distance modulus of the cluster of (m?M)V =13.25±0.08. Stars: binaries: eclipsing, binaries – stars: individual: NV CMa – open clusters and asso- ciations: individual: NGC 2243 1 Introducti