CRIRES User Manual
Doc. Number: ESO-254264
Doc. Version: P109.4
Issued on:
2021-12-01
Page:
41 of 99
Document Classification: ESO Internal Use [Confidential for Non-ESO Staff]
was somewhat higher (~0.2 pixel over 30 min) following metrology alignment than it was
without metrology (0.05 pixel over 30 min);; see
Figure
33
. This effect is still being
investigated and several mitigation strategies are under consideration, but users should
keep in mind that and alignment of data obtained within 15 min of the application of
metrology may be degraded due to this effect.
Figure 33: The pixel shift in dispersion vs. time after the change of the wavelength setting
and/or application of metrology (labelled as "metro") is shown for two wavelength settings.
The effect is being investigated and characterized.
4.6.3 Wavelength calibration
According to the required precision, the wavelength calibration can be done by using
different methods. For an accuracy corresponding to ~5 pixels, the start and end
wavelengths and the derived dispersion for each detector is sufficient.
In most wavelength settings, both emission and absorption sky lines can be used for
absolute wavelength calibration. The presence of sky lines in the desired wavelength setting
can be checked by using the ETC.
The pipeline produces absolute wavelength solutions based on the Uranium-Neon (UNE)
lamp up to ~2500 nm;;
the wavelengths are for vacuum.
Given the lack of suitable
emission lines of the Uranium-Neon lamp in the L- and M-band (>2500 nm), the pipeline
will not produce any wavelength solution there.
The use of gas cells (i.e., SGC or N
2
O, see 3.2.3.1) can be considered for high precision
wavelength calibration. The pipeline, however, does not calculate any wavelength solution
derived from gas cell data;; this is left to the user.
4.6.4 Flat Fielding
Flats field exposures are taken with the Halogen lamp. Once the user specifies the required
NDIT and the maximum flux, the DIT and NDIT is automatically determined by the template.
