Correcting Radial Velocities for Starspot-induced Jitter in the CARMENES Survey

Activity-induced radial velocity variations (RV jitter) are the primary obstacle for the detection of lower mass exoplanets in late-type main-sequence stars. Photospheric activity features such as cool spots, and to some extent also hot faculae, on the stellar disc can distort the spectral line profiles and create RV jitter that may imitate or obscure the signatures of genuine planetary companions. A detailed understanding and modelling of starspot jitter is thus extremely important to avoid false-positive planet detections and erroneous estimates of the parameters of alleged planets.

We have developed a method for disentangling astrophysical systematics caused by starspot-induced jitter from RV signals by taking advantage of the wide spectral range of CARMENES (0.52 to 0.96 µm for the visible and 0.96 to 1.71 µm for the near-infrared) in order to extract planetary signals in the presence of an activity signal.

The method exploits the fact that the RV signal induced by a planetary companion should be consistent over the whole wavelength range of the spectrograph, while spot-induced RV jitter is wavelength dependent due to the varying contrast between the hot photosphere and cool spots.

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