Linking Stellar Coronal Activity and Rotation at 500 Myr: A Deep Chandra Observation of M37

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 ($P_{\mathrm{rot}}$). M37 was observed almost continuously for five days, for a total of 440.5 ksec, to measure stellar X-ray luminosities ($L_{\mathrm{X}}$), 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 $P_{\mathrm{rot}}$, 278 with X-ray detections, and 76 with both. We calculate Rossby numbers, $R_o=P_{\mathrm{rot}}/\tau$, where $\tau$ is the convective turnover time, and ratios of the X-ray-to-bolometric luminosity, $L_{\mathrm{X}}/L_{\mathrm{bol}}$, to minimize mass dependencies in our characterization of the rotation-coronal activity relation at 500 Myr. We find that fast rotators, for which $R_o<0.09\pm 0.01$, show saturated levels of activity, with log($L_{\mathrm{X}}/L_{\mathrm{bol}}$)$=-3.06\pm 0.04$. For $R_o\ge 0.09\pm 0.01$, activity is unsaturated and follows a power law of the form $R_o^{\beta }$, where $\beta$=$-2.03_{-0.14}^{+0.17}$. 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 $M_{\odot }$, $P_{\mathrm{rot}}$ in the range 0.4$-$12.8 d, and $L_{\mathrm{X}}$ in the range 10${}^{28.4-30.5}$ erg s${}^{-1}$. Our results make M37 a new benchmark open cluster for calibrating the ARAR at ages of $\approx$500 Myr.

21 pages, 22 figures, 8 tables, 2 machine-readable tables (MRT)

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Cited by in corpus (15)

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• MESA models with magnetic braking
• Magnetic braking with MESA evolutionary models in the single star and LMXB regimes
• The Ca II H&K Rotation-Activity Relation in 53 mid-to-late type M-Dwarfs
• Solar Angular Momentum Loss Over the Past Several Millennia
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• Chromospheric and Coronal Activity in the 500-Myr-old Open Cluster M37: Evidence for Coronal Stripping?
• The Contribution of Alpha Particles to the Solar Wind Angular Momentum Flux in the Inner Heliosphere
• The Factory and the Beehive. V. Chromospheric and Coronal Activity and Its Dependence on Rotation in Praesepe and the Hyades
• The strongly irradiated planets in Praesepe
• Activity and Rotation of Nearby Field M Dwarfs in the TESS Southern Continuous Viewing Zone