Characterizing and Mitigating the Impact of Telluric Absorption in Precise Radial Velocities

TL;DR

This paper analyzes how Earth's atmospheric absorption affects the precision of radial velocity measurements crucial for detecting Earth-like exoplanets, and evaluates methods to mitigate telluric contamination across different wavelengths.

Contribution

It characterizes telluric effects on RV precision and compares mitigation strategies, highlighting the potential of space missions for near-infrared observations.

Findings

Telluric contamination can be suppressed to 1-10 cm/s in optical wavelengths.

Residual telluric effects in red and near-infrared can cause m/s level errors.

Space-based observations can eliminate systematic telluric errors in these wavelengths.

Abstract

Precise radial velocity (PRV) surveys are important for the search of Earth analogs around nearby bright stars. Such planets induce a small stellar reflex motion with RV amplitude of $\sim$10 cm/s. Detecting such a small RV signal poses important challenges to instrumentation, data analysis, and the precision of astrophysical models to mitigate stellar jitter. In this work, we investigate an important component in the PRV error budget - the spectral contamination from the Earth's atmosphere (tellurics). We characterize the effects of telluric absorption on the RV precision and quantify its contribution to the RV budget over time and across a wavelength range of 350 nm - 2.5$\mu$m. We investigate the effectiveness in mitigating tellurics using simulated spectra of a solar twin star with telluric contamination over a year's worth of observations, and we extracted the RVs using two commonly adopted algorithms: dividing out a telluric model before performing cross-correlation or Forward Modeling the observed spectrum incorporating a telluric model. We assume various degrees of cleanness in removing the tellurics, including mimicking the lack of accurate knowledge of the telluric lines by using a mismatched line profile to model the "observed" tellurics. We conclude that the RV errors caused by telluric absorption can be suppressed to close to or even below the photon-limited precision in the optical region, especially in the blue, around 1-10 cm/s. At red through near-infrared wavelengths, however, the residuals of tellurics can induce an RV error on the m/s level even under the most favorable assumptions for telluric removal, leading to significant systematic noise in the RV time series and periodograms. If the red-optical or near-infrared becomes critical in the mitigation of stellar activity, systematic errors from tellurics can be eliminated with a space mission such as EarthFinder.