Monday

Detailed knowledge of stellar activity is crucial for understanding stellar dynamos, as well as pushing exoplanet radial-velocity detection limits towards Earth analogue confirmation. We directly compare archival High Accuracy Radial velocity Planet Searcher (HARPS) spectra taken at the minimum in α Cen B’s activity cycle to a high-activity state when clear rotational modulation of log R'HK is visible. Relative to the inactive spectra, we find a large number of narrow pseudo-emission features in the active spectra with strengths that are modulated on the rotation period of the star. These features most likely originate from plage, spots or a combination of both and demonstrate the need to better understand the effects that activity changes can have on spectral lines.

Furthermore, we see evidence that some of the lines originating from the ‘active immaculate’ photosphere appear broader relative to the ‘inactive immaculate’ case. This may be due to enhanced contributions of, for example, magnetic bright points to these lines, which then causes additional line broadening. For exoplanet detections the inclusion of lines affected by magnetic activity or showing pseudo-emission features to CCF (cross-correlation function) masks may add additional stellar jitter to RV measurements, reducing the detectability of smaller, more Earth-like, planetary signals.