A vigorous activity cycle mimicking a planetary system in HD200466

TL;DR

This study investigates the stellar activity cycle of HD200466's primary star, demonstrating how activity-induced RV variations can mimic planetary signals, and emphasizes the importance of activity indicators in exoplanet detection.

Contribution

It presents the first detailed analysis of a vigorous activity cycle in HD200466, showing how stellar activity can produce RV signals similar to exoplanets and proposing a method to distinguish them.

Findings

Detected a 1300-day activity cycle in HD200466's primary.

Showed that stellar activity can mimic planetary signals in RV data.

Established Halpha line as a useful activity indicator.

Abstract

Stellar activity can be a source of radial velocity (RV) noise and can reproduce periodic RV variations similar to those produced by an exoplanet. We present the vigorous activity cycle in the primary of the visual binary HD200466, a system made of two almost identical solar-type stars with an apparent separation of 4.6 arcsec at a distance of 44+/-2 pc. High precision RV over more than a decade, adaptive optics (AO) images, and abundances have been obtained for both components. A linear trend in the RV is found for the secondary. We assumed that it is due to the binary orbit and once coupled with the astrometric data, it strongly constrains the orbital solution of the binary at high eccentricities (e~0.85) and quite small periastron of ~21 AU. If this orbital motion is subtracted from the primary radial velocity curve, a highly significant (false alarm probability <0.1%) period of about 1300 d is obtained, suggesting in a first analysis the presence of a giant planet, but it turned out to be due to the stellar activity cycle. Since our spectra do not include the Ca~II resonance lines, we measured a chromospheric activity indicator based on the Halpha line to study the correlation between activity cycles and long-term activity variations. While the bisector analysis of the line profile does not show a clear indication of activity, the correlation between the Halpha line indicator and the RV measurements identify the presence of a strong activity cycle.