Long-term stellar activity and radial velocity variations of the harps m-dwarf sample

J. Gomes da Silva

Abstract.
The relationship between stellar chromospheric activity and variations in the ob- served radial velocity (RV) of stars is still an Achilles heel in the Doppler spectroscopy extrasolar planet searches. It is widely known that activity is able to difficult the detection of planets by contributing to noise or even simulate keplerian-like RV signals which might resemble the presence of a companion. Since other stars are known to have magnetic activity cycles similar to that of the Sun and activity variations can be responsible for RV changes, it is extremely important to understand this connection from an exoplanet search point of view.
It was recently demonstrated that for the case of the Sun these cycles can induce periodic RVs of around 10 m/s. This is the order of magnitude of the amplitudes induced by orbiting low mass planets. Furthermore, it was shown that there is a correlation between long-term activity and RV that is dependent of spectral type: the RV of F-types is more influenced by activity than that of K-type stars. Although recent studies suggested that these cycles are not related to the RV variations for K-stars at the ~1 m/s level, this influence is not fully accessed for the case of M dwarfs, which could behave differently.
This type of stars are becoming an important target for RV surveys. Due to their low mass, it is easier to detect planet candidates of lower masses and at the star’s habitable zone. It is therefore very important to understand the influence of this type of stellar intrinsic noise that could affect the measured RV. Here we present a study of the long time-scale activity variations of a sample of M dwarfs from the HARPS M dwarf planet search survey. We measured four known activity indices and compared them with RV with the objective of establishing whether RV can be influenced by long-term activity for this type of stars.

XXI Encontro Nacional de Astronomia e Astrofisica
Coimbra, Portugal
September 2011

Type: Poster