Correcting HIRES radial-velocities for systematic errors

We use publicly-available radial velocities (RVs) from the HIRES spectrograph to identify and correct for minute ( 1 m/s) systematic RV variations. By averaging the RVs of different quiet stars that were observed each night, we calculate instrumental nightly zero-point RVs, and find small but significant variations on three different timescales. In addition, we find an average small intra-night RV drift. We correct the HIRES RVs for the systematic effects, and investigate the impact of the correction. Our findings highlight the importance of observing quiet stars on a nightly basis, even in the era of self-calibrated and stabilized RV spectrographs.