BEBOP III. Observations and an independent mass measurement of Kepler-16 (AB) b -- the first circumbinary planet detected with radial velocities

TL;DR

This paper reports the first radial velocity detection of a circumbinary planet, Kepler-16b, using SOPHIE spectrograph data, demonstrating the method's viability for discovering more such planets and measuring their masses independently.

Contribution

It provides the first independent radial velocity measurement of a circumbinary planet, confirming its mass and demonstrating the method's potential for future discoveries.

Findings

First RV detection of a circumbinary planet Kepler-16b

Achieved 1.5 m/s precision on binary and planetary signals

Detected a long-term magnetic cycle signal in the data

Abstract

The radial velocity method is amongst the most robust and most established means of detecting exoplanets. Yet, it has so far failed to detect circumbinary planets despite their relatively high occurrence rates. Here, we report velocimetric measurements of Kepler-16A, obtained with the SOPHIE spectrograph, at the Observatoire de Haute-Provence's 193cm telescope, collected during the BEBOP survey for circumbinary planets. Our measurements mark the first radial velocity detection of a circumbinary planet, independently determining the mass of Kepler-16~(AB)~b to be $0.313 \pm 0.039\,{\rm M}_{\rm Jup}$, a value in agreement with eclipse timing variations. Our observations demonstrate the capability to achieve photon-noise precision and accuracy on single-lined binaries, with our final precision reaching $\rm 1.5~m\,s^{-1}$ on the binary and planetary signals. Our analysis paves the way for more circumbinary planet detections using radial velocities which will increase the relatively small sample of currently known systems to statistically relevant numbers, using a method that also provides weaker detection biases. Our data also contain a long-term radial velocity signal, which we associate with the magnetic cycle of the primary star.