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Paper: Rotation and Activity in the Praesepe Open Cluster
Volume: 448, 16th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun
Page: 1165
Authors: Lemonias, J. J.; Agüeros, M. A.; Covey, K. R.; Law, N. M.; Kraus, A. L.; Palomar Transient Factory Collaboration
Abstract: We use new rotation periods obtained by the Columbia/Cornell/Caltech Palomar Transient Factory (PTF; Law et al. 2009) survey of open clusters and archival activity measurements to examine the relation between rotation and activity in the 600 Myr open cluster Praesepe. Our analysis makes use of the updated and expanded catalog of Praesepe members constructed by Kraus & Hillenbrand (2007) and of rotation periods measured for 40 late-K to mid-M dwarfs from PTF optical monitoring of the cluster from 2010 Feb to 2010 May (see Covey et al., these proceedings). Previous studies of activity in Praesepe have suggested that it is under-luminous in X-rays compared to the similarly aged Hyades, implying that Praesepe stars are less magnetically active than their Hyades counterparts. However, we find that members of Praesepe follow the expected relation between rotational velocity and X-ray luminosity, where LX ∝ (v sin i)2, although we caution that the X-ray data for Praesepe stars with measured Prot is sparse. In addition to archival X-ray observations (sensitive to coronal activity), we collect Hα measurements for cluster members, allowing us to probe chromospheric magnetic activity. We recover the trend found in field stars that L/Lbol saturates before LX/Lbol does (Delfosse et al. 1998; Covey et al. 2008), suggesting once again that the activity levels of Praesepe stars are not anomalous. Here again, however, a more extensive set of measurements is required, and we are conducting a comprehensive spectroscopic survey of Praesepe members to complete the census of magnetic activity in the cluster.
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