The Kepler Mission was designed to find transiting, Earth-like exoplanets, by continuously observing over 100,000 stars in a field centered in the constellation of Cygnus. Two years into the mission, it is also providing an extraordinarily rich collection of time-series data for studying variability of stars in our Galaxy, especially low-amplitude variability.
On-line tools are becoming available to study this variability. One of the most powerful is the NASA Star and Exoplanet Database’s (NStED)’s periodogram tool. A periodogram finds periodicities present in time-series data sets, and the associated probability that an individual period arises by chance. NStED serves all the public time-series data released by Kepler (permanently archived at the Multimission Archive at the Space Telescope Science Instiutute), and allows users to calculate periodograms of Kepler data by clicking links on search results pages.
We show one example here – the time-series data and periodogram of the star KIC 12253350. It is a late type pulsating star, whose variations in light are caused by regular swelling and contracting of its outer layers. The periodogram identifies a peak at a period of 1.65 days – the sharp spike in the bottom figure.
To replicate this analysis, go to http://nsted.ipac.caltech.edu/applications/ETSS/Kepler_index.html, type in 12253350 in the Kepler ID box, and hit the button labeled “View.” You will see the light curve, and a button at the bottom called “Compute Periodogram.” Hit that button to see the periodogram.
Finally, Martin Nicholson of Shropshire, United Kingdom has assembled a very nice web page called “Data Mining the Kepler Mission”, which shows in more detail how to navigate the Kepler data set.
Disclosure: I am the Project Manager for NStED. I wish to thank Ms. Marcy Harbut for contributing material to this post.