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

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.

Stellar activity correction using PCA decomposition of shells

“…4.2.1). However, it is really unlikely for those contaminations to solely provide a Dopplerian component without presenting simultaneously non-Dopplerian effects (Huélamo et al 2008;Meunier et al 2010;Reiners et al 2013;Marchwinski et al 2015;Fischer et al 2016;Davis et al 2017;Barnes et al 2017;Zechmeister et al 2018;Dumusque 2018;Cretignier et al 2020a;Lisogorskyi et al 2021;Lienhard & Mortier 2021) that would be modelled by the PCA shell basis components. As a consequence, the best option remains to decorrelated in the time-domain α DS (t) with the other coefficients α(t), an option also chosen by the SCALPEL method (Collier Cameron et al 2021).…”

Revisiting ϵ Eridani with NEID: Identifying New Activity-sensitive Lines in a Young K Dwarf Star

“…These 42 lines spanning HARPS's wavelength range of 3780-6910 Å (Pepe et al 2000), with features that exhibit periodicity at the star's rotation period, are a useful tool for investigating how certain lines are tied to stellar activity. For example, Lisogorskyi et al (2020) used the line list published by W18 as a reference to help identify active regions of the spectra in order to explore how the removal of these regions helps improve RV calculations. The identification of activity-sensitive lines is therefore a first step toward uncovering the complex relationships between spectral features and stellar activity, and eventually disentangling this information from the RVs.…”