A multiwavelength view of the open cluster NGC 2527: discovery of active stars

Abstract

Star clusters are ideal platforms for categorizing X-ray emitting stars and to study X-ray emission as a function of stellar age and activity. We present a comprehensive study of an open star cluster, NGC 2527, by combining data from XMM-UVOT-Gaia. Cluster membership of stars and their photometry are taken from Gaia and cross-matched with XMM and UVOT detections. We estimate the age of NGC 2527 as ∼630 Myr, reddening as E(B − V) = 0.13 mag, and a distance of 642 ± 30 pc using PARSEC isochrones. We detect five sub-subgiants and five bandgap stars, which defy single star evolution. We estimate the temperature, mass, radius, and luminosity of 53 single stars and 10 potential binary stars using a python code that fits single and composite Kurucz spectra to broad-band spectral energy distribution. Among the 12 X-ray emitting members, we find that five are potential RS CVn-type binaries, two are potential FK Comae type of red giant branch (RGB) stars, and five are main sequence (MS) stars with high coronal activity. Members with strong UV emission comprise one RGB star and several MS stars with UV excess suggestive of chromospheric activity. Based on comparison with other clusters, we tentatively suggest that X-ray luminosity of both RS CVn and contact binaries increases with age, suggesting that more active binaries are present in older clusters as compared to younger clusters. This study suggests possible presence of W UMa and FK Comae-type stars in younger (age 630 Myr) clusters.