Data Reduction Frequently Asked Questions

Should I expect the FWHM of the cross-correlation function (CCF) of ESPRESSO to be smaller than that of HARPS on the same target, due to ESPRESSO's higher resolution?

The FWHM of the individual lines measured by ESPRESSO is smaller than that of HARPS, as expected due to the instrument's higher resolution. However, the HARPS and ESPRESSO pipelines use different algorithms with different line weighting schemes for the computation of the CCF's FWHM. These differences make the HARPS data reduced with the HARPS pipeline to have smaller FWHM than the ESPRESSO data of the same target processed with the ESPRESSO pipeline.