An Activity–Rotation Relationship and Kinematic Analysis of Nearby Mid-to-Late-Type M Dwarfs
Using spectroscopic observations and photometric light curves of 238 nearby M dwarfs from the MEarth exoplanet transit survey, we examine the relationships between magnetic activity (quantified by Hα emission), rotation period, and stellar age. Previous attempts to investigate the relationship between magnetic activity and rotation in these stars were hampered by the limited number of M dwarfs with measured rotation periods (and the fact that v sin i measurements probe only rapid rotation). However, the photometric data from MEarth allows us to probe a wide range of rotation periods for hundreds of M dwarf stars (from shorter than one to longer than 100 days). Over all M spectral types that we probe, we find that the presence of magnetic activity is tied to rotation, including for late-type, fully convective M dwarfs. We also find evidence that the fraction of late-type M dwarfs that are active may be higher at longer rotation periods compared to their early-type counterparts, with several active, late-type, slowly rotating stars present in our sample. Additionally, we find that all M dwarfs with rotation periods shorter than 26 days (early-type; M1–M4) and 86 days (late-type; M5–M8) are magnetically active. This potential mismatch suggests that the physical mechanisms that connect stellar rotation to chromospheric heating may be different in fully convective stars. A kinematic analysis suggests that the magnetically active, rapidly rotating stars are consistent with a kinematically young population, while slow-rotators are less active or inactive and appear to belong to an older, dynamically heated stellar population.
© 2015 The American Astronomical Society. Received 2015 February 12; accepted 2015 August 22; published 2015 October 2. The authors acknowledge Elisabeth Newton, Dylan Morgan, and the other members of the Boston Area Drinking And Society for Stars of Elfin Stature for useful conversations in the preparation of this manuscript. A.A.W. acknowledges the support of NSF grants AST-1109273 and AST-1255568 and the Research Corporation for Science Advancementʼs Cottrell Scholarship. K.L.W. acknowledges the support of the Boston University UROP program and the Clare Boothe Luce scholarship. Z.K.B.T. gratefully acknowledges support from the Torres Fellowship for Exoplanetary Research. The MEarth Team gratefully acknowledges funding from the David and Lucille Packard Fellowship for Science and Engineering (awarded to D.C.). This material is based upon work supported by the National Science Foundation under grants AST- 0807690, AST-1109468, and AST-1004488 (Alan T. Waterman Award). This publication was made possible through the support of a grant from the John Templeton Foundation. The opinions expressed in this publication are those of the authors and do not necessarily reflect the views of the John Templeton Foundation. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship (to JSP) under grant No. DGE-1144469.
Submitted - 1509.01590v1.pdf
Published - West_2015p3.pdf