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dc.contributor.advisorBerger, Edoen_US
dc.contributor.advisorCharbonneau, Daviden_US
dc.contributor.authorNewton, Elisabeth R.en_US
dc.date.accessioned2017-07-25T14:39:11Z
dc.date.created2016-05en_US
dc.date.issued2016-05-19en_US
dc.date.submitted2016en_US
dc.identifier.citationNewton, Elisabeth R. 2016. The Evolution of Rotation and Magnetism in Small Stars Near the Sun. Doctoral dissertation, Harvard University, Graduate School of Arts & Sciences.en_US
dc.identifier.urihttp://nrs.harvard.edu/urn-3:HUL.InstRepos:33493355
dc.description.abstractDespite the prevalence of M dwarfs, the smallest and most common type of main sequence star, 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. I obtained low-resolution (R = 2000) near-infrared spectra of 447 nearby mid-to-late M dwarfs. I measured their absolute radial velocities with an accuracy of 4.4 km/s by exploiting telluric lines to establish an absolute wavelength calibration. I estimated their metallicities from the equivalent width of the sodium absorption feature at 2.2 μm to a precision of 0.12 dex, and from 2MASS colors to a precision of 0.15 dex. Using stars with radii measured from interferometry, I showed that the equivalent widths of aluminum and magnesium absorption features can be used to infer K and M dwarf temperatures to a precision of 69 K, and radii to 0.027 R⊙. I applied these relations to planet-hosting stars from Kepler, showing that the typical planet is 15% larger than inferred when adopting stellar parameters from other recent catalogs. Using photometry from the MEarth-North Observatory, I measured rotation periods from 0.1 to 140 days for 387 M dwarfs. I found 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 found that rapid rotators (P < 10 days) are < 2 Gyr, and that the slowest are on average 5 ± 3 Gyr old. I then showed that for early M dwarfs the typical stellar rotation period at 5 Gyr coincides with the orbital period at which habitable planets are found, and I suggest that mid-to-late M dwarfs are optimal targets around which to search for habitable-zone planets. I obtained optical spectra of 247 nearby M dwarfs, and measured the strength of the chromospheric Hα emission line. I identified a well-defined boundary in the mass–period plane that separates active and inactive M dwarfs. Hα activity is therefore a simple, accessible diagnostic for stellar rotation period, and I present a mass–period relation for inactive M dwarfs. I found a significant (p value < 10e−4) positive correlation between Hα emission strength and photometric variability amplitude, which implies that stars with stronger magnetic fields have both higher levels of chromospheric activity and larger or more abundant spots. I suggest that fully convective stars maintain rapid rotation rates and saturated magnetic activity for about 2 Gyr. They then undergo rapid angular momentum evolution upon reaching some critical threshold. Only upon reaching long rotation periods (around 70 days for a 0.2 M⊙ star) do their magnetic activity levels drop below what is required for Hα to be seen in emission. The stars I have observed in pursuit of this work are the nearest low-mass stars. As such they are the best targets around which to search for habitable, rocky worlds, and my work provides the means to constrain the sizes, temperatures, and ages of those planets.en_US
dc.description.sponsorshipAstronomyen_US
dc.format.mimetypeapplication/pdfen_US
dc.language.isoenen_US
dash.licenseLAAen_US
dc.subjectPhysics, Astronomy and Astrophysicsen_US
dc.titleThe Evolution of Rotation and Magnetism in Small Stars Near the Sunen_US
dc.typeThesis or Dissertationen_US
dash.depositing.authorNewton, Elisabeth R.en_US
dc.date.available2017-07-25T14:39:11Z
thesis.degree.date2016en_US
thesis.degree.grantorGraduate School of Arts & Sciencesen_US
thesis.degree.levelDoctoralen_US
thesis.degree.nameDoctor of Philosophyen_US
dc.contributor.committeeMemberConroy, Charles R.en_US
dc.contributor.committeeMemberLatham, David W.en_US
dc.contributor.committeeMemberMamajek, Eric E.en_US
dc.type.materialtexten_US
thesis.degree.departmentAstronomyen_US
dash.identifier.vireohttp://etds.lib.harvard.edu/gsas/admin/view/1104en_US
dc.description.keywordsastronomy; astrophysics; stellar physics; observational astronomy; photometry; spectroscopy; exoplanets; stellar rotation; stellar magnetic activity; stellar parameters; stars: low massen_US
dash.author.emailelisabeth.r.newton@gmaii.comen_US
dash.identifier.orcid0000-0003-4150-841Xen_US
dash.contributor.affiliatedNewton, Elisabeth R
dc.identifier.orcid0000-0003-4150-841X


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