The He I D3 Line as a Proxy for Magnetic Activity using EXPRES Solar Observations

TL;DR

This paper investigates the He I D3 line as a new proxy for stellar magnetic activity, demonstrating its strong correlation with magnetic flux and radial velocities in solar observations, which could enhance exoplanet detection.

Contribution

The study introduces the He I D3 line as a reliable activity indicator, providing a new tool to distinguish stellar activity from planetary signals in radial velocity data.

Findings

He I D3 line correlates with magnetic flux and RVs

He I D3 line can serve as a stellar activity proxy

Potential to improve exoplanet detection accuracy

Abstract

Stellar activity remains one of the primary challenges in the detection and characterization of low-mass exoplanets, as it can induce radial velocity (RV) variations that mask or mimic planetary signals. Identifying reliable activity proxies is essential in order to distinguish stellar variability from genuine planetary signatures. In this study, we examine the variability of the chromospheric He I D3 line in high-resolution solar spectra and assess its potential as an activity indicator. We find a strong correlation between the He I D3 line intensity variation and the Sun's unsigned magnetic flux derived from SDO HMI data as well as with the solar RVs. Our results suggest that the He I D3 line offers a promising and straightforward proxy for magnetic activity, which may complement existing stellar activity indicators. Its inclusion could help disentangle stellar signals in RV measurements and ultimately improve the detection of Earth-like exoplanets.