Exploring the robustness of Keplerian signals to the removal of active and telluric features

TL;DR

This study investigates how removing activity- and telluric-affected spectral lines from high-resolution spectra affects the detection and robustness of planetary signals in radial velocity measurements, using Monte Carlo simulations.

Contribution

It introduces a spectral line removal method to improve the robustness of Keplerian signals against stellar activity and telluric contamination, validated through simulations and application to different star types.

Findings

Removing activity- and telluric-sensitive lines enhances planetary signal significance.

The method's effectiveness varies with star type, being more beneficial for K stars than F stars.

Monte Carlo simulations confirm the approach's utility in assessing signal robustness.

Abstract

We examine the influence of activity- and telluric-induced radial velocity signals on high resolution spectra taken with an iodine absorption cell. We exclude 2 Angstrom spectral chunks containing active and telluric lines based on the well characterised K1V star Alpha Centauri B and illustrate the method on Epsilon Eridani - an active K2V star with a long period low amplitude planetary signal. After removal of the activity- and telluric-sensitive parts of the spectrum from the radial velocity calculation, the significance of the planetary signal is increased and the stellar rotation signal disappears. In order to assess the robustness of the procedure, we perform Monte Carlo simulations based on removing random chunks of the spectrum. Simulations confirm that the removal of lines impacted by activity and tellurics provides a method for checking the robustness of a given Keplerian signal. We also test the approach on HD 40979 which is an active F8V star with a large amplitude planetary signal. Our Monte Carlo simulations reveal that the significance of the Keplerian signal in the F star is much more sensitive to wavelength. Unlike the K star the removal of active lines from the F star greatly reduces the radial velocity precision. In this case, our removal of a K star active lines from an F star does not a provide a simple useful diagnostic because it has far less radial velocity information and heavily relies on the strong active lines.