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 \sim 1 m s ^ { -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 m s ^ { -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 \pm 0.1 m s ^ { -1 } , and the slow zero-point variations have a typical magnitude of \lesssim 1 m s ^ { -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 \pm 0.004 m s ^ { -1 } hr ^ { -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 .