Characterizing and Mitigating Telluric Absorption in Precise Radial Velocities: Dependence on Spectral Type

The precise radial velocity (PRV) method for detecting exoplanets aims to detect the stellar reflex motion from terrestrial habitable zone planets, which produce Doppler signals with velocity semi-amplitudes on the order of 10 cm/s for a G star and closer to 25 cm/s for an M dwarf. There are various instrumentation and astrophysical challenges that have precluded such detections to date, including stellar surface activity such as starspots, plages, and granulation. We present simulations to quantify the additional impact of telluric absorption lines from the Earth’s atmosphere upon PRV high-resolution spectroscopic measurements of nearby stars across the entire visible and near-infrared spectrum. Telluric absorption lines can bias the measurements of PRVs, and introduce systematic errors that can obscure the stellar reflex motion from orbiting terrestrial habitable zone planets. We assess how different telluric mitigation techniques can compensate for the presence of tellurics, including telluric correction division, cross-correlation and forward modeling. We find that forward modeling outperforms cross-correlation. By working with noiseless simulated spectra, we can place a floor on the induced PRV systematic error given a set of assumptions such as the telluric absorption line profile accuracy and mitigation approach. We find that in the red-optical, telluric absorption can introduce systematic errors on the order of 10 cm/s, and up to ~1 m/s for the near-infrared for a G star and on the order of 16 cm/s and up to ~1.5 m/s in the NIR for an M dwarf. 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.