Radial velocity stability

The results from previous tests, including the use of the experimental fiber shaker, have now been added to the documentation on the web. The shaker was improved such that you can determine what state the machine is in and see if it is running or not. Still, a way to use this in the sequencer needs to implemented such that it will be possible to make observing scripts using the shaker.

To monitor the stability and be able to assess possible improvements a proper test and monitoring program is being set-up. Radial-velocity standard star measurements will be obtained on Nordic service nights to study the long-term and short-term stability of the instrument. Incoming data are automatically reduced with FIESTool, and a dedicated analysis tool will be setup.

Some more detailed results of observations of a specific standard star in previous observing runs over the period 2009-2011 were provided by Lars Buchhave (NBI Copenhagen). There are clear offsets (at the 20-30 m/s level) in the average measured radial velocity between observing runs in different years, most probably related to external effects (mostly human interventions in the spectrograph and detector, e.g., pumping). Standard-star measurements should be able to correct for these offsets. From the data it is found that for the high-resolution fiber the intra-run stability (as given by the standard deviation of the standard star measurements) is always below 10 m/s, while for the medium-resolution fiber the results are consistent with our tests, showing a stability of $\sim$10m/s with the old bundle, and $\sim$25m/s with the new bundle.

Thomas Augusteijn 2013-05-10