A multi-wavelength view of the open cluster NGC 2527: Discovery of active stars

Nevil Shah, K. P. Singh, Annapurni Subramaniam

Published 2020-02-28Version 1

Star clusters are ideal platforms for categorising 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, NGC2527, 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 NGC2527 as ~630 Myr, reddening as E(B-V)=0.13 mag, and a distance of 642+/-30 pc using PARSEC isochrones. We detect 5 sub-subgiants and 5 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 which fits single and composite Kurucz spectra to broad-band Spectral Energy Distribution. Among the 12 X-ray emitting members, we find 5 are potential RS CVn type binaries, 2 are potential FK Comae type of RGB stars, and 5 are main sequence (MS) stars with high coronal activity. Members with strong UV emission comprise of 1 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 more active binaries are present in older clusters as compared to younger clusters. This study suggests the possible presence of W UMa and FK Comae type stars in younger (age~630 Myr) clusters.