SCYON Abstract

Received on February 27 2010

Variable Stars in the Field of the Open Cluster NGC 2204

AuthorsM. Rozyczka (1), J. Kaluzny (1), P. Pietrukowicz (1,2), W. Pych (1), B. Mazur (1), M. Catalan (2), and I.B. Thompson (3)
Affiliation(1) Nicolaus Copernicus Astronomical Center, ul. Bartycka 18, 00-716 Warszawa, Poland
(2) Departamento de Astronomía y Astrofísica, Pontificia Universidad Católica de Chile, Av. Vicuna Mackenna 4860, Macul, Santiago, Chile
(3) The Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA91101, USA
To appear inActa Astronomica
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Abstract

e present an analysis of NGC2204-S892 -- a new detached eclipsing binary composed of two late K dwarfs. Based on three photometric campaigns launched in 2008 we obtained 5 light curves (3 in V, 1 in B and 1 in I), and derived an orbital period of 0.451780±0.000001d. We also obtained 20 VLT/UVES spectra, enabling accurate radial velocity measurements. The derived masses and radii of the components (m1 = 0.733 ± 0.005M(sun) and R1 = 0.72 ± 0.01R(sun); m2 = 0.662 ± 0.005M(sun) and R2 = 0.68 ± 0.02R(sun) are consistent with the empirical mass-radius relationship established recently for lower main sequence stars in binary systems; in particular we find that both stars are oversized compared to theoretical models. NGC2204-S892 is very active: both components show variable emission in Hα and Hβ and are heavily spotted, causing the light curve to show appreciable changes on a timescale of weeks. Our results add to the increasing evidence that the observed inflation of the radii of K and M stars is related to high levels of magnetic activity.