J/ApJ/809/161 X-ray obs. and membership probabilities of M37 (Nunez+, 2015) ================================================================================ 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., West A.A. =2015ApJ...809..161N (SIMBAD/NED BibCode) ================================================================================ ADC_Keywords: X-ray sources ; Photometry, ugriz ; Cross identifications ; Clusters, open ; Stars, masses Keywords: open clusters and associations: individual: M37; stars: activity; stars: coronae; stars: rotation; X-rays: individual: 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_rot_). M37 was observed almost continuously for five days, for a total of 440.5ks, to measure stellar X-ray luminosities (L_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_rot_, 278 with X-ray detections, and 76 with both. We calculate Rossby numbers, R_0_=P_rot_/{tau}, where {tau} is the convective turnover time, and ratios of the X-ray-to-bolometric luminosity, L_X_/L_bol_, to minimize mass dependencies in our characterization of the rotation-coronal activity relation at 500Myr. We find that fast rotators, for which R_0_<0.09+/-0.01, show saturated levels of activity, with log(L_X_/L_bol_)=-3.06+/-0.04. For R_0_>=0.09+/-0.01, activity is unsaturated and follows a power law of the form R_0_^{beta}^, where {beta}=-2.03^+0.17^_-1.14_. 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 0.4-1.3M_{sun}_, P_rot_ in the range 0.4-12.8 days, and L_X_ in the range 10^28.4-30.5^erg/s. Our results make M37 a new benchmark open cluster for calibrating the ARAR at ages of ~500Myr. Description: The central field of M37 was observed five separate times between 2011 November 14 20:58 and 2011 November 19 15:31 UTC for a total of 440.5ks with the Advanced CCD Imaging Spectrometer (ACIS; obsID 13655, 13656, 13657, 14366 and 14367). ME08 (Messina+, 2008, J/A+A/483/253) selected images from the survey taken with the 1.0m telescope at the Mt. Lemmon Optical Astronomy Observatory, AZ, of a 22.2"x22.2" area centered on M37, and used both the Scargle-Press and CLEAN periodogram techniques to measure variability for stars with 1310% afterglow events Note (2): K-S statistic ranges as follows: a = PKS<0.05 b = 0.005=0.2 to be candidate cluster members. See section 3.3 for further explanations. Note (3): Pmem<0.2 but we consider it cluster member, based on the fact that it has a soft X-ray counterpart. Note (4): Object type as follows: * = Star from Messina et al. (2008, J/A+A/483/253) RGB = Red giant from Mermilliod et al. (2008, J/A+A/485/303). FM06 = Massive star from Frinchaboy & Majewski (2006, J/AJ/136/118). NS02 = Massive star from Nilakshi & Sagar (2002, J/A+A/381/65). Note (5): References are: NS02 = Nilakshi & Sagar (2002, J/A+A/381/65). FM06 = Frinchaboy & Majewski (2006, J/AJ/136/118). M08 = Mermilliod et al. (2008, J/A+A/485/303). K05 = Kalirai et al. (2005ApJ...618L.123K; in Simbad). -------------------------------------------------------------------------------- History: From electronic version of the journal References: Nunez & Agueros Paper II. 2016ApJ...830...44N Cat. J/ApJ/830/44 ================================================================================ (End) Prepared by [AAS], Emmanuelle Perret [CDS] 11-Dec-2015