Linking stellar coronal activity and rotation at 500 MYR: A deep Chandra observation of M37

Journal Article · Thu Aug 20 04:00:00 EDT 2015 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/809/2/161· OSTI ID:22882747

Núñez, Alejandro; Agüeros, Marcel A.; Bowsher, Emily C.; Douglas, Stephanie T. ^[1]; Covey, Kevin R. ^[2]; Hartman, Joel D. ^[3]; Kraus, Adam L. ^[4]; López-Morales, Mercedes; Saar, Steven H. ^[5]; Pooley, David A. ^[6]; Posselt, Bettina ^[7]; West, Andrew A. ^[8]

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1. Department of Astronomy, Columbia University, 550 West 120th Street, New York, NY 10027 (United States)
2. Department of Physics and Astronomy, Western Washington University, 516 High Street, Bellingham, WA 98225 (United States)
3. Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Princeton, NJ 08544 (United States)
4. Department of Astronomy, University of Texas at Austin, 2515 Speedway, Stop C1400, Austin, TX 78712 (United States)
5. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02183 (United States)
6. Department of Physics, Sam Houston State University, Farrington Building, Suite 204, Hunstville, TX 77341 (United States)
7. Department of Astronomy and Astrophysics, Penn State University, 525 Davey Lab, University Park, PA 16802 (United States)
8. Department of Astronomy, Boston University, CAS 422A, 725 Commonwealth Ave, Boston, MA 02215 (United States)

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{sub rot}). M37 was observed almost continuously for five days, for a total of 440.5 ks, to measure stellar X-ray luminosities (L{sub 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{sub rot}, 278 with X-ray detections, and 76 with both. We calculate Rossby numbers, R{sub o}= P{sub rot}/τ, where τ is the convective turnover time, and ratios of the X-ray-to-bolometric luminosity, L{sub X}/L{sub 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{sub o}<0.09±0.01, show saturated levels of activity, with log(L{sub X}/L{sub bol})= −3.06±0.04. For R{sub o}⩾0.09±0.01, activity is unsaturated and follows a power law of the form R{sub o}{sup β}, where β = −2.03{sub −0.14}{sup +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{sub ⊙}, P{sub rot} in the range 0.4–12.8 days, and L{sub X} in the range 10{sup 28.4−30.5} erg s{sup −1}. Our results make M37 a new benchmark open cluster for calibrating the ARAR at ages of ≈500 Myr.

• OSTI ID: 22882747
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 809; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United Kingdom
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
BENCHMARKS
BOLOMETERS
EMISSION
LUMINOSITY
MASS
PROBABILITY
ROTATION
STARS
STELLAR CORONAE
X-RAY DETECTION