An XMM-Newton observation of the young open cluster NGC 2547: coronal activity at 30 Myr

Abstract

We report on XMM-Newton observations of the young open cluster NGC 2547 which allow us to characterize coronal activity in solar-type stars, and stars of lower mass, at an age of 30 Myr. X-ray emission is seen from stars at all spectral types, peaking among G stars at luminosities (0.3-3 keV) of L_x≃ 10^30.5 erg s^-1 and declining to L_x≤ 10^29.0 erg s^-1 among M stars with masses ≥0.2 M_⊙. Coronal spectra show evidence for multi-temperature differential emission measures and low coronal metal abundances of Z≃ 0.3. The G- and K-type stars of NGC 2547 follow the same relationship between X-ray activity and Rossby number established in older clusters and field stars, although most of the solar-type stars in NGC 2547 exhibit saturated or even supersaturated X-ray activity levels. The median levels of L_x and L_x/L_bol in the solar-type stars of NGC 2547 are very similar to those in T-Tauri stars of the Orion Nebula cluster (ONC), but an order of magnitude higher than in the older Pleiades. The spread in X-ray activity levels among solar-type stars in NGC 2547 is much smaller than in older or younger clusters.