Rotation and activity in the solar-type stars of NGC 2547 |
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| Authors: | R D Jeffries E J Totten D J James |
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| Institution: | Department of Physics, Keele University, Keele, Staffordshire ST5 5BG;Department of Physics and Astronomy, University of St Andrews, St Andrews, Fife KY16 9SS;Observatoire de Genève, Chemin de Maillettes 51, CH-1290 Sauverny, Switzerland |
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| Abstract: | We present high-resolution spectroscopy of a sample of 24 solar-type stars in the young (15–40 Myr), open cluster NGC 2547. We use our spectra to confirm cluster membership in 23 of these stars, to determine projected equatorial velocities and chromospheric activity, and to search for the presence of accretion discs. We find examples of both fast ( v e sin i >50 km s−1) and slow ( v e sin i <10 km s−1) rotators, but no evidence for active accretion in any of the sample. The distribution of projected rotation velocities is indistinguishable from the slightly older IC 2391 and IC 2602 clusters, implying similar initial angular momentum distributions and circumstellar disc lifetimes. The presence of very slow rotators indicates either that long (10–40 Myr) disc lifetimes or internal differential rotation are needed, or that NGC 2547 (and IC 2391/2602) were born with more slowly rotating stars than are presently seen in even younger clusters and associations. The solar-type stars in NGC 2547 follow a similar rotation–activity relationship to that seen in older clusters. X-ray activity increases until a saturation level is reached for v e sin i >15–20 km s−1. We are unable to explain why this saturation level, of log( L x L bol)≃−3.3, is a factor of 2 lower than in other clusters, but rule out anomalously slow rotation rates or uncertainties in X-ray flux calculations. |
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| Keywords: | stars: activity stars: late-type stars: rotation open clusters and associations: individual: NGC 2547 X-rays: stars |
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