Photometric Variability in Kepler Target Stars. II. An Overview of Amplitude, Periodicity, and Rotation in First Quarter Data

TL;DR

This study analyzes stellar variability in Kepler's first quarter data, revealing that about half of over 150,000 stars show periodic behavior related to rotation and starspots, with distinct patterns across different star types.

Contribution

It provides a comprehensive overview of stellar variability in Kepler data, including procedures for data treatment and insights into periodic behaviors across star classes.

Findings

Approximately 50% of stars exhibit periodic variability up to two weeks.

K and M dwarfs show higher fractions of periodic behavior than G dwarfs.

Giants display quasi-periodic but not strictly periodic behavior.

Abstract

We provide an overview of stellar variability in the first quarter of data from the Kepler mission. The intent of this paper is to examine the entire sample of over 150,000 target stars for periodic behavior in their lightcurves, and relate this to stellar characteristics. These data constitute an unprecedented study of stellar variability given its great precision and complete time coverage (with a half hour cadence). Because the full Kepler pipeline is not currently suitable for a study of stellar variability of this sort, we describe our procedures for treating the "raw" pipeline data. About half of the total sample exhibits convincing periodic variability up to two weeks, with amplitudes ranging from differential intensity changes less than 10^{-4} up to more than 10 percent. K and M dwarfs have a greater fraction of period behavior than G dwarfs. The giants in the sample have distinctive quasi-periodic behavior, but are not periodic in the way we define it. Not all periodicities are due to rotation, and the most significant period is not necessarily the rotation period. We discuss properties of the lightcurves, and in particular look at a sample of very clearly periodic G dwarfs. It is clear that a large number of them do vary because of rotation and starspots, but it will take further analysis to fully exploit this.