Insight into the structure and physics of M dwarf stars through determination of the rotation, metallicities, and radii of the nearby population
Despite the prevalence of M dwarfs, their fundamental properties--their sizes, compositions, and ages--are not well-constrained. Empirical determination of these properties is important for gaining insight into their stellar structure, magnetic field generation, and angular momentum evolution. Knowledge of the stellar parameters is also key to characterizing planetary systems. I used observations to empirically constrain the properties of nearby, mid-to-late M dwarfs targeted by the MEarth transiting planet survey. I obtained low-resolution (R=2000) NIR spectra of 450 M dwarfs using SpeX on IRTF. I measured their absolute radial velocities with an accuracy of 4 km/s by exploiting telluric lines to establish an absolute wavelength calibration, and developed techniques to estimate M dwarf metallicities from K-band spectral line equivalent widths (EWs) or 2MASS colors to 0.15 dex. Using stars with interferometric radii, I showed that H-band EWs can be used to infer K and M dwarf temperatures to 69K, and radii to 0.027Rsun. I applied these relations to planet-hosting stars from Kepler, showing that the typical planet is 15% larger than is inferred if adopting other stellar parameters. Using photometry from the MEarth-North Observatory, I measured rotation periods from 0.1 to 150 days for 350 M dwarfs. There is a prevalence of stable spot patterns, and no correlation between period and amplitude for fully-convective stars. Using galactic kinematics as a proxy for age, I demonstrated a smooth age-rotation relation. I found that rapid rotators (P<10 days) are <2 Gyr, and that the slowest are on average 5+-3 Gyr old. I will discuss the extension of this work to the southern hemisphere, which utilizes FIRE on Magellan and the MEarth-South Observatory. MEarth acknowledges funding from the NSF, the David and Lucile Packard Foundation and the John Templeton Foundation. ERN was supported by the NSF GRFP. This work includes observations obtained at the Infrared Telescope Facility, operated by the U. of Hawaii, and the Magellan Telescopes at Las Campanas Observatory, Chile. I recognize the significant role of Mauna Kea within the indigenous Hawaiian community, and acknowledge the opportunity to conduct these observations.
American Astronomical Society Meeting Abstracts #227
- Pub Date:
- January 2016