Modeling the Environmental Drift of High Resolution Spectrographs to Enhance the RV Precision

We present a study of the instrumental drift in two high-resolution spectrographs for stellar radial velocity measurements. We use a simple model that allows one to calculate the expected drift from the measurements of temperature, pressure, and humidity of the atmosphere. By comparing the real drift with the predictions of the model, we can identify and possibly correct instabilities in the instruments produced by effects other than the atmosphere. The method allows us to improve the control of the instruments and to enhance the radial velocity performances of those instruments, which do not include simultaneous wavelength calibration. By applying this method, we measure improvements in radial velocity precision for PUCHEROS+ from 30 to 15 m s⁻¹, and obtain a limiting radial velocity precision of 7 m s⁻¹ in PLATOSpec.