EDP Sciences
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Volume 399, Number 1, February III 2003
Page(s) 99 - 104
Section Stellar clusters and associations
DOI http://dx.doi.org/10.1051/0004-6361:20021704

A&A 399, 99-104 (2003)
DOI: 10.1051/0004-6361:20021704

Search for variable stars in the open cluster NGC 2539

K. J. Choo1, 2, S.-L. Kim2, T. S. Yoon1, M.-Y. Chun2, H. Sung3, B.-G. Park2, H. B. Ann4, M. G. Lee5, Y.-B. Jeon2 and I.-S. Yuk2

1  Department of Astronomy and Atmospheric Sciences, Kyungpook National University, Daegu 702-701, Korea
2  Korea Astronomy Observatory, Daejeon 305-348, Korea
3  Department of Astronomy and Space Science, Sejong University, Seoul 143-747, Korea
4  Department of Earth Science, Pusan National University, Busan 609-735, Korea
5  Astronomy Program, SEES, Seoul National University, Seoul 151-742, Korea

(Received 17 July 2002 / Accepted 7 November 2002 )

We present UBVI absolute and V-band time-series CCD photometric results for the intermediate-age open cluster NGC 2539. From the empirical zero-age main sequence and theoretical isochrone fitting in color-color and color-magnitude diagrams, we estimated the physical parameters of this cluster as follows: the color excess of $E(B-V)=0.06 \pm 0.03$, the distance modulus of $(V-M_{V})_{0}=10.2 \pm 0.1$ and the age of $\log t = 8.8$ (~630 Myr). By carefully examining the time-series images, we discovered seven new variable stars in the observed cluster field. Considering the light curves, periods and positions on the color-magnitude diagram, we classified them as five eclipsing binary stars, one $\delta$ Scuti star and one $\gamma$ Doradus candidate. The $\gamma$ Doradus candidate might not be a cluster member because it is located redder by about $\Delta (B-V) = 0.2$ than the cool edge of $\gamma$ Doradus instability strip.

Key words: open clusters and association: individual: NGC 2539 -- stars: Hertzsprung-Russell (HR) and C-M diagrams -- stars: binaries: eclipsing

Offprint request: K. J. Choo, kjchoo@knu.ac.kr

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