@article{4fce43550bbb4af8b64fe7277e8bcb5d,
title = "Calibrating iodine cells for precise radial velocities",
abstract = "High fidelity iodine spectra provide the wavelength and instrument calibration needed to extract precise radial velocities (RVs) from stellar spectral observations taken through iodine cells. Such iodine spectra are usually taken by a Fourier Transform Spectrometer (FTS). In this work, we investigated the reason behind the discrepancy between two FTS spectra of the iodine cell used for precise RV work with the High Resolution Spectrograph (HRS) at the Hobby–Eberly Telescope (HET). We concluded that the discrepancy between the two HRS FTS spectra was due to temperature changes of the iodine cell. Our work demonstrated that the ultra-high resolution spectra taken by the TS12 arm of the Tull Spectrograph One at McDonald Observatory are of similar quality to the FTS spectra and thus can be used to validate the FTS spectra. Using the software IodineSpec5, which computes the iodine absorption lines at different temperatures, we concluded that the HET/HRS cell was most likely not at its nominal operating temperature of 70°C during its FTS scan at National Institute of Standards and Technology or at the TS12 measurement. We found that extremely high resolution echelle spectra (R > 200,000) can validate and diagnose deficiencies in FTS spectra. We also recommend best practices for temperature control and nightly calibration of iodine cells.",
author = "Wang, {Sharon Xuesong} and Wright, {Jason T.} and Phillip Macqueen and Cochran, {William D.} and Doss, {David R.} and Gibson, {Coyne A.} and Schmitt, {Joseph R.}",
note = "Funding Information: The work herein has used 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. We also thank the California Planet Survey group for providing some of their iodine calibration data. Funding Information: We thank Anita Cochran and the astronomers who used the Cassegrain instruments at night during our TS12 runs (VIRUS-W for the first run and IGRINS for the second). We are deeply grateful for the help and support by the staff at McDonald Observatory?our TS12 runs would not be successful without their devoted work. S.X.W. is grateful for Iouli Gordon for his comments and for bringing to our attention the software package IodineSpec5. We greatly appreciate the work by Stephen Redman and Gillian Nave at NIST of performing the FTS scans of the HET/HRS cell as well as the data reduction. We thank Ming Zhao and Kimberly M.S.Cartier for conducting the TS12 observing run on the McDonald 2.7m iodine cell and the HET/HRS cell and Ming Zhao?s help on reducing the TS12 data. We also thank Gillian Nave, Larry Ramsey, and Suvrath Mahadevan for their helpful comments and suggestions. 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. This work herein has used observations obtained at the Hobby?Eberly Telescope at McDonald Observatory, and the HET partners include University of Texas at Austin, the Pennsylvania State University, the Ludwig Maximilians Universit?t, and the Georg August Universit?t. The work herein has used 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. We also thank the California Planet Survey group for providing some of their iodine calibration data. 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). Funding Information: 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. Publisher Copyright: {\textcopyright} 2019. The Astronomical Society of the Pacific. All rights reserved. Printed in the U.S.A.",
year = "2020",
month = jan,
doi = "10.1088/1538-3873/ab5021",
language = "English (US)",
volume = "132",
journal = "Publications of the Astronomical Society of the Pacific",
issn = "0004-6280",
publisher = "University of Chicago",
number = "1007",
}