LINKING STELLAR CORONAL ACTIVITY and ROTATION at 500 MYR: A DEEP CHANDRA OBSERVATION of M37

Alejandro Núñez, Marcel A. Agüeros, Kevin R. Covey, Joel D. Hartman, Adam L. Kraus, Emily C. Bowsher, Stephanie T. Douglas, Mercedes López-Morales, David A. Pooley, Bettina Posselt, Steven H. Saar, Andrew A. West

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Abstract

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.

Original languageEnglish (US)
Article number161
JournalAstrophysical Journal
Volume809
Issue number2
DOIs
StatePublished - Aug 20 2015

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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