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Over the past decades hollow-cathode lamps have been calibration standardsfor spectroscopic measurements. Advancing to cm/s radial velocity precisionswith the next generation of instruments requires more suitable calibrationsources with more lines and less dynamic range problems. Fabry-Perotinterferometers provide a regular and dense grid of lines and homogeneousamplitudes making them good candidates for next generation calibrators. Weinvestigate the usefulness of Fabry-Perot etalons in wavelength calibration,present an algorithm to incorporate the etalon spectrum in the wavelengthsolution and examine potential problems. The quasi periodic pattern ofFabry-Perot lines is used along with a hollow-cathode lamp to anchor thenumerous spectral features on an absolute scale. We test our method with theHARPS spectrograph and compare our wavelength solution to the one derived froma laser frequency comb. The combined hollow-cathode lamp/etalon calibrationovercomes large distortion (50 m/s) in the wavelength solution of the HARPSdata reduction software. Direct comparison to the laser frequency comb bearsdifferences of only maximum 10 m/s. Combining hollow-cathode lamps withFabry-Perot Interferometers can lead to substantial improvements in thewavelength calibration of echelle spectrographs. Etalons can provide economicalalternatives to the laser frequency comb, especially for smaller projects.

Calibrating echelle spectrographs with Fabry-Perot etalons