Resolving power monitoring

October 2004: This section is outdated. We are currently working on an update that will display the results of the Resolving Power monitoring which are being updated in an off-line database. Since the beginning of 2003, all measurements show Resolving Power above 200,000.

The resolving power is measured from the FWHM of the narrowest, reliably measured Th line(s) in the spectrum. Measurements are always done after optimisation of the instrument setup. They do not take into account the intrinsic thermally broadened line width; therefore the values displayed here are lower limits to the true resolving power.

The degradation can be calculated from the thermal broadening v = sqrt(2kT/m) of Thorium lines assuming an operating temperature of the ThAr lamp of 120 C.

Example: at a wavelength of 5400 Å (which is used here as a standard reference wavelength for the CES) the intrinsic width of Thorium lines degrades the measurable resolving power by about 1.0%, 0.35%, and 0.19% for the high-, medium-, and low-resolution image slicers, respectively.

Changes in this nominal resolving power can be due to imperfect instrument alignment (not fully accounted for in the setup) and also to aging of the ThAr lamp, the latter making calculations based on the above formula rather unreliable.

Graphical form:

Upper panel: High resolution image slicer

Circles: measurements taken at the standard reference wavelength 5400 Å.
Crosses: measurements taken at other wavelengths.

Lower panel: Medium resolution image slicer

[Click here to download ps file]

Last update: 04 Oct 2004 Comments to