HARPS Fibre Stability Monitoring

Monitoring the relative RV stability of the two fibres.

The capability to track variation of the instrument profile using the reference fibre is one of the main design concept of HARPS. This implies that when both fibres are illuminated by the same spectrum their behaviour should be the same, in particular changes on the radial velocity (RV) measured by one fibre should be indistinguishible by changes measured by the other fibre.
Periodic tests of the relative stability of the two fibres are part of the HARPS calibration plan. These tests are performed by illuminating both fibres with ThAr light from the same lamp, and by measuring the RV drift on each fibre as a function of telescope position. Ideally no significative difference between the drift from the two fibres should be found.
In the following table we show a summary of the measurements. Numbers lower than 0.5m/s are below the noise level of the calibration. Monitoring started in 2003, but publication of the results on the web begins on June 2006.