Astrophys. J., 809, 161 (2015/August-3)
Linking stellar coronal activity and rotation at 500 Myr: a deep Chandra observation of M37.
NUNEZ A., AGUEROS M.A., COVEY K.R., HARTMAN J.D., KRAUS A.L., BOWSHER E.C., DOUGLAS S.T., LOPEZ-MORALES M., POOLEY D.A., POSSELT B., SAAR S.H. and WEST A.A.
Abstract (from CDS):
Empirical calibrations of the stellar age-rotation-activity relation (ARAR) rely on observations of the co-eval populations of stars in open clusters. We used the Chandra X-ray Observatory to study M37, a 500-Myr-old open cluster that has been extensively surveyed for rotation periods (). M37 was observed almost continuously for five days, for a total of 440.5 ks, to measure stellar X-ray luminosities (), a proxy for coronal activity, across a wide range of masses. The cluster's membership catalog was revisited to calculate updated membership probabilities from photometric data and each star's distance to the cluster center. The result is a comprehensive sample of 1699 M37 members: 426 with, 278 with X-ray detections, and 76 with both. We calculate Rossby numbers,, where τ is the convective turnover time, and ratios of the X-ray-to-bolometric luminosity,, to minimize mass dependencies in our characterization of the rotation-coronal activity relation at 500 Myr. We find that fast rotators, for which, show saturated levels of activity, with log(). For, activity is unsaturated and follows a power law of the form, where β =. This is the largest sample available for analyzing the dependence of coronal emission on rotation for a single-aged population, covering stellar masses in the range 0.4-1.3, in the range 0.4-12.8 days, and in the range. Our results make M37 a new benchmark open cluster for calibrating the ARAR at ages of Myr.
open clusters and associations: individual: M37 - stars: activity - stars: coronae - stars: rotation - X-rays: individual: M37
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<Available at CDS (J/ApJ/809/161): table3.dat table5.dat>
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