An investigation into the radial velocity variability of GJ 581 - On the significance of GJ 581g

TL;DR

This study confirms four planets orbiting GJ 581 using combined HARPS and Keck data, but finds no evidence supporting the existence of the proposed GJ 581g planet, highlighting the importance of data analysis techniques.

Contribution

It demonstrates the effectiveness of Fourier pre-whitening and combined data analysis in confirming planetary signals and assessing their significance.

Findings

Four planetary signals confirmed around GJ 581.

Combined data increases signal significance.

No evidence found for GJ 581g.

Abstract

We investigate the radial velocity variation of GJ 581 based on measurements from the HARPS and Keck HIRES spectrographs. A Fourier pre-whitening procedure is able to extract four planetary signals in the HARPS data and two from the Keck data. Combining both data sets increases the significance of the four planet signals found by HARPS. This indicates that the Keck data also supports the presence of four planets. A periodogram analysis of the residual radial velocity measurements after removal of the four planetary signals shows several periodic signals that are significant when assessing the false alarm probability via a bootstrap. However, it is demonstrated that these are not due to planetary companions. This analysis is able to confirm the presence of four planets around GJ 581, but not the presence of GJ 581g.