The HIRES spectrograph, mounted on the 10-m Keck-I telescope, belongs to a small group of radial-velocity (RV) instruments that produce stellar RVs with long-term precision down to ∼1 ms−1. In 2017, the HIRES team published 64,480 RVs of 1,699 stars, collected between 1996 and 2014. In this bank of RVs, we identify a sample of RV-quiet stars, whose RV scatter is <10 ms−1, and use them to reveal two small but significant nightly zero-point effects: a discontinuous jump, caused by major modifications of the instrument in August 2004, and a long-term drift. The size of the 2004 jump is 1.5±0.1 ms−1, and the slow zero-point variations have a typical magnitude of ≲1 ms−1. In addition, we find a small but significant correlation between stellar RVs and the time relative to local midnight, indicative of an average intra-night drift of 0.051±0.004 ms−1hr−1. We correct the 64,480 HIRES RVs for the systematic effects we find, and make the corrected RVs publicly available. Our findings demonstrate the importance of observing RV-quiet stars, even in the era of simultaneously-calibrated RV spectrographs. We hope that the corrected HIRES RVs will facilitate the search for new planet candidates around the observed stars.
@article{arxiv.1810.02986,
title = {Correcting HIRES radial velocities for small systematic errors},
author = {Lev Tal-Or and Trifon Trifonov and Shay Zucker and Tsevi Mazeh and Mathias Zechmeister},
journal= {arXiv preprint arXiv:1810.02986},
year = {2019}
}