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ESPaDOnS: spectral domain and resolution http://webast.ast.obs-mip.fr/magnetisme/espadons_new/resol.html
An average number of about 50 lines per order (about 2,000
lines in total) are automatically searched for by the reduction
routine and identified using reference lists of thorium line
wavelengths; from these, wavelength calibration polynomials
are produced over the full spectral range. The typical accuracy
of this calibration is found to be of order of 0.06pxl or 150m/s at
each given wavelength.
The few remaining neon lines blooming the ccd in the red part
of the domain do not really affect the precision of the
calibration procedure.
Spectral resolution
By measuring the full width at half maximum of the individual
thorium lines (reflecting mostly the instrumental broadening),
one can determine the spectral resolution of ESPaDOnS in the
selected instrument configuration (the reduction code does it
automatically).
The graph on the right shows an example of such thorium lines
(the strongest of the 3 being the ThI line at 550.75385nm). The
full line indicates the wavelength calibrated spectrum around
this line derived with ESPaDOnS being set in polarimetric
mode, while the dashed line depicts that obtained in the ’object
only’ spectroscopic mode. The respective line widths (at half
maximum) are respectively equal to 8.3 and 6.9pm, in
agreement with the spectral resolutions of 68,000 and 81,000
associated to these modes.
These resolutions correpond to velocity elements of 4.4 and
3.7km/s respectively, to be compared to the 2.6km/s ccd pixel
size and the 1.8km/s bin size on which the spectra are
recovered.
© Jean-François Donati, last update May 5 2004
2 of 2 08/07/04 11:29 PM