New discoveries of transiting extrasolar planets are reported weekly. Ground based surveys as well as space borne observatories like CoRoT and Kepler are responsible for filling the statistical voids of planets on distant stellar systems. The ultimate goal is the discovery of a habitable planet and maybe a second Earth.
I want to discuss the stellar activity and its impact on the discovery of extrasolar planets. Up to now the discovery of small rocky planets called "Super-Earths" like CoRoT-7b and Kepler-10b are the only exceptions. The question arises, why among over 500 detected and verified planets the amount of smaller planets is strikingly low. Our statistics, we collected so far on the distribution of planetary masses and radii, is obviously biased by observational effects. Another explanation besides that the verification of small planets is an intriguing task, is the high level of stellar activity that has been observed.
Stellar activity can be observed at different time-scales from long term irradiance variations similar to the well known solar cycle, over stellar rotation in the regime of days, down to the observations of acoustic modes in the domain of minutes. But also non periodic events like flares or the activity signal of the granulation can prevent the detection of a transiting Earth sized planet.
I will describe different methods to detect transit-like signals in stellar photometric data, the different influences introduced by the star, the observer and their impact on the success. Different filtering techniques will be discussed to improve the transit detection capability and to separate the transit signal from the intrinsic stellar signal.
Finally different mathematical models and approximations of transit signals will be examined on their sensibility of stellar activity.
I present a statistical overview of stellar activity in the CoRoT dataset. The influence of stellar activity will be analysed on different transiting planets: CoRoT-2b, CoRoT-4b und CoRoT-6b.
Stellar activity can prevent the successful detection of a transiting planet, where CoRoT-7b marks the borderline. Future missions like Plato will be required to provide long-term observations with mmag precision to overcome the limitations set by active stars in our Galactic neighbourhood.
