Name/Affiliation: Alejandro Nunez (Columbia University)
Deep X-ray imaging of M37: a better Hyades
Although it has been known for decades that rotation and magnetic activity in main- sequence stars evolve with age, a quantitative description of the age-rotation-activity relation (ARAR) is still a work in progress. Empirical calibrations of this relation rely critically on the coeval populations of stars in open clusters. The Hyades has been studied extensively to benchmark the ARAR at 600 Myr; for example, ROSAT observations were used to characterize coronal X-ray emission, a tracer of a starís overall magnetic activity, in middle-aged clusters. X-ray observations of the Hyades and Praesepe, another ~600 Myr cluster, differ substantively, casting doubt on the universality of the age-coronal activity relation. We present preliminary results from a 450 ksec Chandra X-ray observation of M37, another Hyades-like, 500-Myr-old open cluster. To fully exploit these data and the extensive catalog of optical rotation periods measured for stars in the M37 field, we begin by revisiting the clusterís membership. At a distance of 1.5 kpc, M37 is a difficult target for ground-based proper motion measurements; we therefore calculate updated membership probabilities for cluster and field stars based on their position in a color-magnitude diagram and their distance from the cluster center. We then match our list of M37 cluster members to our ACIS-I detections, focusing on those stars for which we have rotation periods. With rotation periods and X-ray detections for a substantial sample of M37 members, this study will decouple the age-rotation and rotation-activity relationships at ~500 Myr, and help determine the universality of the ~500-600 Myr ARAR.