Abstract

I will first discuss a new technique to derive extremely precise radial velocities (RV) from high-resolution spectrographs. By deriving the RV of each individual line in a HARPS spectrum, one can see that some spectral lines are affected by important variations that cannot be associated to planetary or stellar signals. These variation are caused by the instrument itself, and excluding the affected spectral lines when cross correlating the stellar spectrum with a synthetic template can improve the RV precision. In a second part, I will present a new model that estimates the effect of stellar activity on RV measurements. This model, based on observations of the Sun, includes the inhibition of convection which is one of the main cause of the activity-induced RV variation. When comparing with observations, our model reproduces the activity-related variation seen in photometry, RV, bisector and full width of half maximum. This model can therefore be used to fit observed data, which gives us access to interesting stellar parameters like stellar inclination.