Photometric study and detection of variable stars in the open clusters – I. NGC 6866




We present results of a variability search in the intermediate-age open cluster NGC 6866 from 29 nights over two observing seasons. We find 28 periodic variables, of which 19 are newly identified. The periods of these variables, which have V magnitudes from 11.5 to 19.3 mag, range from ∼48 min to 37 d. We detected several δ Scuti stars, some of which are of high amplitude, as well as γ Doradus and rotational variables, and eclipsing binaries. In order to study the physical properties of the cluster, we obtained UBVRI photometry of all the stars on a good photometric night. The radial distribution of the stellar surface density shows that the cluster has a radial extent of about 7 arcmin (∼3 pc) with a peak density of 5.7 ± 0.7 stars arcmin−2 at the cluster centre. The colour–colour diagram indicates a reddening of E(BV) = 0.10 mag towards NGC 6866. A distance of ∼1.47 kpc and an age of ∼630 Myr are estimated from the colour–magnitude diagram using the theoretical isochrones of solar metallicity.