Stellar cycles from photometric data: CoRoT stars

Abstract

Context. Until a few years ago, the amplitude variation in the photometric data had been explored to a limited extent mainly because of time resolution and photometric sensitivity limitations. This investigation is now possible thanks to the Kepler and CoRoT databases which provide a unique set of data for studying the nature of stellar variability cycles.
Aims: The present study characterizes the amplitude variation in a sample of main-sequence stars with light curves collected using CoRoT exofield CCDs.
Methods: We analyze potential stellar activity cycles by studying the variability amplitude over small boxes. The cycle periods and amplitudes were computed based on the Lomb-Scargle periodogram, harmonic fits, and visual inspection. As a first application of our approach, we considered the photometric data for 16 CoRoT FGK main sequence stars, revisited during the IRa01, LRa01 and LRa06 CoRoT runs.
Results: The 16 CoRoT stars appear to follow the empirical relations between activity cycle periods (P_cyc) and the rotation period (P_rot) found by previous works. In addition to the so-called A (active) and I (inactive) sequences previously identified, there is a possible third sequence, here named S (short-cycles) sequence. However, recovery fractions estimated from simulations suggest that only a half of our sample has confident cycle measurements. Therefore, more study is needed to verify our results, and Kepler data will clearly be useful for such a study. Overall, our procedure provides a key tool for exploring the CoRoT and Kepler databases to identify and characterize stellar cycle variability.

The CoRoT space mission was developed and is operated by the French space agency CNES, with the participation of ESA's RSSD and Science Programmes, Austria, Belgium, Brazil, Germany, and Spain.