The+CoRoT+and+Kepler+Revolution+in+Stellar+Variability+Studies

//The CoRoT and Kepler Revolution in Stellar Variability Studies.//

Format: short introductory presentation (showing CoRoT and Kepler results) followed by open questions and discussion.

Organizers: P. Degroote and J. Debosscher

Abstract:

The CoRoT and Kepler missions are delivering stellar light curves of unprecedented time sampling and photometric precision. The main goal of these missions is the detection of exoplanets using the occultation method, requiring photometric follow-up of thousands of stars, most of them of a-priori unknown nature. The resulting light curve databases are very well suited for studying stellar variability in all its forms, including stellar pulsations. The past years, several efforts have been undertaken to identify and classify the variables in these huge datasets in an automated way. Very good results are obtained with these methods, especially for the identification of new members of already known variability types. More challenging is the discovery of new variability types, mixed types of variability (e.g. pulsators in eclipsing binary systems) and a-typical members of known variability classes. Essential for these tasks are efficient time series analysis methods, able to describe a large variety of light curves in a homogeneous way. Most methods currently used, focus on periodic signals, while many light curves show non-periodic or quasi-periodic behaviour. We need to come up with different methods to describe the key characteristics of those light curves.

In the case of ground based light curves, the main question was often whether or not significant variability was detected. Now, the main question is what kind of variability we see, since almost all stars show clear variability at CoRoT's and Kepler's precision levels. Recent results from CoRoT and Kepler suggest that the subdivision of pulsating stars into a number of clear-cut classes is a very incomplete representation of the true situation. For example, CoRoT and Kepler data of stars located in the SPB and beta-Cephei instability domains in the HR diagram, show variability very different from the type of pulsations we expect to see for those objects. The variability landscape is clearly much more diverse than previously thought, and class boundaries are not that clear-cut. The challenge is to relate different light curve morphologies as much as possible to the physics causing the variability, and to investigate when and how light curve morphology can be used to classify stars.

//Suggested Questions://
 * how to parametrize irregular and time dependent variability (which methods are suitable, how are the parameters connected to stellar physics)?
 * how to disentangle or distinguish different phenomena occurring in stellar light curves: e.g., pulsations and rotational modulation, ellipsoidal variability, eclipses, instrumental variability...?
 * how to deal with unresolved spectral features?
 * methods suitable for large databases and/or large datasets?
 * redefinition or update of stellar variability classes needed?
 * how to combine information from different instruments?