Author ORCID Identifier

https://orcid.org0000-0002-0558-1305

Date of Award

12-10-2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics and Astronomy

First Advisor

Sebastien Lepine

Abstract

The K2 mission has targeted large numbers of nearby (d < 100 pc) GKM dwarfs selected from the SUPERBLINK proper motion survey (µ > 40 mas yr−1 , V < 20). K2 campaigns 0 through 15 monitored a total of 58,484 of these cool main-sequence stars. We used the auto-correlation function to search for fast rotators by identifying short-period photometric modulations in the K2 light curves. We identified 1,113 candidate fast rotators with rotation periods < 4 days that show light curve modulations consistent with star spots in their photosphere. Their kinematics show low average transverse velocities, suggesting they are part of the local, young disk population. We demonstrate that the M dwarf fast rotators selected from the K2 light curves are significantly more likely to have UV excess, which indicates they are chromospherically active. Based on these results, we discuss the potential of the K2 mission to identify new nearby young GKM dwarfs on the basis of these fast rotation rates.

Using the K2 light curves, we also search for randomly occurring white light flare events as a tracer of magnetic activity. We show that the flare rate appears to be strongly correlated with the amplitude of the star spot fluctuations, which suggests that flares are more frequent when spot coverage on a star is higher. We find a possible correlation between the timing of the flares and the intensity level in the star.

Additionally, the K2 mission targeted low-mass, high-velocity stars selected from the SUPERBLINK catalog. While we expect the rotation rate of these old stars to have slowed down, our search for fast rotators has identified 12 fast-rotator candidates among this subset. We suggest these stars may be tidally locked, close binary systems.

Finally, our search for fast rotators identified 13 eclipsing systems in this old population of low-mass, and presumably metal-poor stars. Six of these systems are reported here for the first time, and are prime targets for calibrating the mass-luminosity and mass-radius relationships in old, metal-poor, low-mass stars.

DOI

https://doi.org/10.57709/13481701

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