CRIRES Quality Control: wavelength calibration

CRIRES Quality Control:
wavelength calibrations

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QC PLOTS
	CURRENT	HISTORY
cross-correlation
ThAr central wavelength
N2O central wavelength
QC1 database (advanced users): browse \| plot
Click on CURRENT to see the current trending (Health Check). Click on HISTORY to see the historical evolution of the trending.

Wavelength calibration for CRIRES can be obtained with several different methods: from sky lines in the science frames, from dedicated wavelength calibration frames using an arc lamp or a gas cell, or from a physical model. This page describes QC checks on arc lamp and gas cell exposures.

CRIRES offers a ThAr arc lamp for measuring emission line spectra and a gas cell which is filled with N2O gas and illuminated by the halogen (flat-field) lamp for absorption line spectra. Wavelength calibration frames are measured during daytime according to the settings used during the night. They are also frequently attached to science OBs. For settings above 2500 nm, wavelength calibrations are usually not taken because the density of sky lines is sufficiently high. For health check purposes, a ThAr exposure with reference wavelength 1090.4 nm and an N2O exposure with 4092.9 nm are measured daily.

In April 2008, a fibre bundle was mounted in front of the ThAr lamp. The ligth is projected as separate traces on the detector.

The pipeline recipe performs a cross-correlation between the observed frame and a template which is derived from the line lists. The cross-correlation value is a unitless number between 0 and 1. A value above 0.2 is regarded as a successful solution. In case of a failure, the recipe gives -1 as cross-correlation result.

Raw ThAr arc lamp frame (until March 2008)

Raw ThAr arc lamp frame with fibres (April 2008 and later)

Raw N2O gas cell frame

top Wavelength calibration parameters

QC1 parameters for CRIRES arc lamp and gas cell exposures are measured for each detector array separately.

QC1 parameters

parameter	QC1 database: table, name	procedure
central wavelength	crires_wave, lambda_cent	wavelength of the central column of the detector (in nm)
dispersion	crires_wave, dispersion	linear dispersion (in nm/pix)
cross-correlation result	crires_wave, xcorr	cross-correlation result

Trending

QC1 parameters for wavelength calibration are trended for the daily health check settings with 1090.4 nm (ThAr) and 4092.9 nm (N2O). Trending consists of the cross-correlation result and of the central wavelength on each detector array.

History

April 2008: fibres are mounted in front of ThAr lamp