Effects of Telluric Contamination in Iodine-calibrated Precise Radial Velocities

Creators: Wang, Sharon Xuesong; Wright, Jason T.; Bender, Chad; Howard, Andrew W.; Isaacson, Howard; Veyette, Mark; Muirhead, Philip S.

Abstract

We characterized the effects of telluric absorption lines on the radial velocity (RV) precision of stellar spectra taken through an iodine cell. To isolate the effects induced by telluric contamination from other stellar, instrumental, or numerical systematic RV noise, we extracted RVs from simulated iodine-calibrated spectra of three RV standard stars regularly observed by Keck/HIRES. We add in water absorption lines according to measured precipitable water vapor (PWV) contents over a one-year period. We conclude that telluric contamination introduces additional RV noise and spurious periodic signals at the level of 10–20 cm s⁻¹, consistent with similar previous studies. Our findings show that forward modeling the telluric lines effectively recovers the RV precision and accuracy, with no prior knowledge of the PWV needed. Such a recovery is less effective when the water absorption lines are relatively deep in the stellar template used in the forward modeling. Overall, telluric contamination plays an insignificant role in typical iodine-calibrated RV programs aiming at ~1–2 m s⁻¹, but we recommend adding modeling of telluric lines and taking stellar template observations on nights with low humidity for programs aiming to achieve a precision of better than 1 m s⁻¹.

Additional Information

© 2019 The American Astronomical Society. Received 2018 November 16; revised 2019 September 11; accepted 2019 September 27; published 2019 November 1. We thank R. Paul Butler and John A. Johnson for providing a copy of their Doppler code and their help with incorporating the code. The authors also thank Debra Fischer for her assistance in this regard and Dr. Paula Coelho for providing the high-resolution, high-sampling M dwarf synthetic spectra. Finally, we thank Drs. Eric Ford, Suvrath Mahadevan, Jim Kasting, and Larry Ramsey for their input to this work. S.X.W. acknowledges support from NASA Earth and Space Science Graduate Fellowship (2014–2016). J.T.W. and S.X.W. acknowledge support from NSF AST-1211441. This work was also partially supported by funding from the Center for Exoplanets and Habitable Worlds, which is supported by the Pennsylvania State University, the Eberly College of Science, and the Pennsylvania Space Grant Consortium. We appreciate the work done by the observers who took the data using Keck/HIRES on HD 185144, HD 10700, and HD 95735, which has enabled this work. The work herein is based on observations obtained at the W. M. Keck Observatory, which is operated jointly by the University of California and the California Institute of Technology. The Keck Observatory was made possible by the generous financial support of the W.M. Keck Foundation. We wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. This work has made use of NASA's Astrophysics Data System Bibliographic Services. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France (Wenger et al. 2000). Software: TERRASPEC (Bender et al. 2012), TAPAS (Bertaux et al. 2014), PHOENIX (v15.5; Hauschildt 1993; Hauschildt & Baron 2006; Baron & Hauschildt 2007).

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Published - Wang_2019_AJ_158_216.pdf

Accepted Version - 1910.00688.pdf

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