Chromatic drift of the Espresso Fabry-Pérot etalon

In the last decade, white-light illuminated Fabry-P\'erot interferometers wave been established as a widely used, relatively simple, reliable, and cost-effective way to precisely calibrate high-resolution echelle spectrographs. However, Terrien et al. (2021) recently reported chromatic drift of interferometer installed at Habitable-zone Planet Finder spectrograph. particular, they found that variation etalon effective gap size is not achromatic usually assumed but in fact depends on wavelength. Here, we present similar study Espresso interferometer. Using daily calibrations spanning period over 2.5 years, also find clear evidence for with an amplitude few cm/s per day has characteristic, quasi-oscillatory dependence We conclude this effect probably caused by aging dielectric mirror coatings expect drifts might affect all used calibration astronomical demonstrate can be measured principle corrected using only standard based hollow cathode lamp spectra.