Asteroseismology of gamma Doradus stars with Kepler

Abstract

Stellar physics is a vital part of modern astronomy. To better understand stars, we must understand not only the stellar surface, but also the stellar interior. We can use the waves propagating in stars to probe stellar inner regions. Asteroseismology, the science that investigates the stellar waves, has been an effective tool to research stellar interiors. I conducted an observational study of the gamma Doradus stars using data from NASA's Kepler mission. These stars have masses between 1.4 and 2.0 solar masses and pulsate mainly in gravity and Rossby modes, showing period spacing patterns in the Fourier spectra. The pulsations are sensitive to the stellar structure near the upper boundary of the convective core, hence they are valuable for understanding the stellar interior. I identified period spacing patterns in more than 600 gamma Dor stars from the 4-yr Kepler data, which allowed me to measure the asymptotic spacings, the near-core rotation rates, and the radial orders. My results show that the stars rotate more slowly than predicted by the theory, and the rotation distribution shows excess at the slow-rotation side for unclear reasons. I also detected the core-to-surface rotation profiles in about 10% stars. The interiors rotate faster than the cores in most stars, but by no more than 5%. I applied my methods to the gamma Dor stars in eclipsing binaries, and compared the near-core rotation periods with the orbital periods. The results show that a star is more likely to be tidally locked if its orbital period is shorter than about 10 days. More slow rotators are seen in the eclipsing binary sample, which might be an explanation of the slow-rotator excess mentioned in the previous paragraph. Several stars have extremely slow core rotation with the orbital periods longer than 100 days, implying a new mechanism interacting between the tidal forces and the g-mode pulsations.