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

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. Coronal temperatures increase with L x , L x / L bol and surface X‐ray flux. The most active solar‐type stars in NGC 2547 have coronal temperatures intermediate between those in the ONC and the most active older zero‐age main‐sequence (ZAMS) stars. We show that simple scaling arguments predict higher coronal temperature in coronally saturated stars with lower gravities. A number of candidate flares were identified among the low‐mass members and a flaring rate [for total flare energies (0.3–3 keV) > 10 34  erg ] of one every 350 +350 −120  ks was found for solar‐type stars, which is similar to rates found in the ONC and Pleiades. Comparison with ROSAT High Resolution Imager (HRI) data taken 7 yr earlier reveals that only 10–15 per cent of solar‐type stars or stars with L x > 3 × 10 29  erg s −1 exhibit X‐ray variability by more than a factor of 2. This is comparable with clusters of similar age but less than in both older and younger clusters. The similar median levels of X‐ray activity and rate of occurrence for large flares in NGC 2547 and the ONC demonstrate that the X‐ray radiation environment around young solar‐type stars remains relatively constant over their first 30 Myr.