Revisiting $\epsilon$ Eridani with NEID: Identifying New Activity-Sensitive Lines in a Young K Dwarf Star

Abstract

Recent improvements in the sensitivity and precision of the radial velocity (RV) method for exoplanets have brought it close, but not quite to, the threshold ($\sim$10 cm/s) required to detect Earth-mass and other potentially habitable planets around Sun-like stars. Stellar activity-driven noise in RV measurements remains a significant hurdle to achieving this goal. While various efforts have been made to disentangle this noise from real planetary signals, a greater understanding of the relationship between spectra and stellar activity is crucial to informing stellar activity mitigation. We use a partially automated method to analyze spectral lines in a set of observations of the young, active star $\epsilon$ Eridani from the high-precision spectrograph NEID, correlate their features (depth, full width at half maximum, and integrated flux) with known activity indicators, and filter and curate for well-behaved lines whose shape changes are sensitive to certain types of stellar activity. We then present a list of 9 lines correlated with the S-index in all three line features, including 4 newly-identified activity-sensitive lines; as well as additional lines correlated with S-index in at least one feature, and discuss the possible implications of the behavior observed in these lines. Our line lists represent a step forward in the empirical understanding of the complex relationships between stellar activity and spectra, and illustrate the importance of studying the time evolution of line morphologies with stabilized spectrographs, in the overall effort to mitigate activity in the search for small, potentially Earth-like exoplanets.

16 pages, 9 figures. For associated data cube, see https://doi.org/10.5281/zenodo.10085919

References in corpus (11)

• The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
• Measuring precise radial velocities on individual spectral lines : II. Dependance of stellar activity signal on line depth
• Hyperfine Splitting in the VALD Database of Spectral-line Parameters
• On-sky commissioning of MAROON-X: A new precision radial velocity spectrograph for Gemini North
• Stellar activity correction using PCA decomposition of shells
• The CARMENES search for exoplanets around M dwarfs: Benchmarking the impact of activity in high-precision radial velocity measurements
• FIESTA II. Disentangling stellar and instrumental variability from exoplanetary Doppler shifts in Fourier domain
• Spectral Line Depth Variability in Radial Velocity Spectra
• Into the Depths: a new activity metric for high-precision radial velocity measurements based on line depth variations
• Accounting for stellar activity signals in radial-velocity data by using Change Point Detection techniques
• The need for a public forecast of stellar activity to optimise exoplanet radial velocity detections & transmission spectroscopy

Cited by in corpus (1)

• Spectral Ratio Analysis: probing of a new suite of stellar activity indicators as a tool for astrophysical noise mitigation