Disentangling Planets and Stellar Activity for Gliese 667C

TL;DR

This study analyzes the impact of stellar activity on radial velocity measurements of Gliese 667C, confirming some planets while attributing others to stellar effects, and clarifying the system's planetary composition.

Contribution

It introduces a method to correct stellar activity effects in RV data, refining planet detections around Gliese 667C.

Findings

Confirmed planets b and c after activity correction

Attribution of the 90-day RV signal to stellar rotation

Did not confirm additional planets previously reported

Abstract

Gliese 667C is an M1.5V star with a multi-planet system, including planet candidates in the habitable zone (HZ). The exact number of planets in the system is unclear, because the existing radial velocity (RV) measurements are known to contain contributions from stellar magnetic activity. Following our analysis of Gliese 581 (Robertson et al. 2014), we have analyzed the effect of stellar activity on the HARPS/HARPS-TERRA RVs of GJ 667C, finding significant RV-activity correlation when using the width (FWHM) of the HARPS cross-correlation function to trace magnetic activity. When we correct for this correlation, we confirm the detections of the previously-observed planets b and c in the system, while simultaneously ascribing the RV signal near 90 days ("planet d") to an artifact of the stellar rotation. We are unable to confirm the existence of the additional RV periodicities described in Anglada-Escude et al. (2013) in our activity-corrected data.