2003A&A...399...99C

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±0.03, the distance modulus of (V-M_V)₀=10.2±0.1 and the age of logt=8.8 (∼630Myr). 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 δ Scuti star and one γ Doradus candidate. The γ Doradus candidate might not be a cluster member because it is located redder by about Δ(B-V)=0.2 than the cool edge of γ Doradus instability strip.