New Methods for Finding Activity-Sensitive Spectral Lines: Combined Visual Identification and an Automated Pipeline Find a Set of 40 Activity Indicators

TL;DR

This paper introduces a new method combining visual and automated techniques to identify over 40 spectral lines sensitive to stellar activity, aiding in distinguishing stellar noise from planetary signals in spectroscopic data.

Contribution

The study presents a novel correlation-based approach to discover activity-sensitive spectral lines, expanding the toolkit for stellar activity diagnostics beyond traditional indicators.

Findings

Identified over 40 new activity-sensitive spectral lines.

Demonstrated the effectiveness of correlation methods on HARPS spectra.

Provided a comprehensive list of activity indicators for future research.

Abstract

Starspots, plages, and activity cycles cause radial velocity variations that can either mimic planets or hide their existence. To verify the authenticity of newly discovered planets, observers may search for periodicity in spectroscopic activity indices such as Ca H & K and H$\alpha$, then mask out any Doppler signals that match the activity period or its harmonics. However, not every spectrograph includes Ca H & K, and redder activity indicators are needed for planet searches around low-mass stars. Here we show how new activity indicators can be identified by correlating spectral line depths with a well-known activity index. We apply our correlation methods to archival HARPS spectra of $\epsilon$ Eri and $\alpha$ Cen B and use the results from both stars to generate a master list of activity-sensitive lines whose core fluxes are periodic at the star's rotation period. Our newly discovered activity indicators can in turn be used as benchmarks to extend the list of known activity-sensitive lines toward the infrared or UV. With recent improvements in spectrograph illumination stabilization, wavelength calibration, and telluric correction, stellar activity is now the biggest noise source in planet searches. Our suite of $> 40$ activity-sensitive lines is a first step toward allowing planet hunters to access all the information about spots, plages, and activity cycles contained in each spectrum.