CRIRES User Manual
Doc. Number: ESO-254264
Doc. Version: P109.4
Issued on:
2021-12-01
Page:
28 of 99
Document Classification: ESO Internal Use [Confidential for Non-ESO Staff]
4. Instrument Performance
4.1 Overview
The sensitivity of the instrument from K up to L and M bands is limited by the thermal
background, while it is limited by the detector performance in the Y, J and H bands. Based
on data collected during the first and second on-sky commissioning runs, as well as in the
integration hall at ESO Garching:
•
Spectral resolution of at least 40,000 and 80,000 can be achieved with slit width of
0.4” and 0.2”, respectively.
•
The throughput is ~15% higher when compared to the oCRIRES.
•
In Y, J, H and K bands, an absolute wavelength repeatability 5 px (RMS) in the main
dispersion is reached without the metrology system, and <0.2px when the metrology
is enabled. In L and M bands, the absolute wavelength repeatability is of the order
of <10 px.
4.2 AO performance
The performance achieved by the MACAO system of CRIRES has been evaluated by
laboratory simulations comparing two cases:
i)
in closed loop with guide star of various
magnitudes and,
ii)
in open loop (i.e., without AO correction). The optimization was done
over the encircled energy on a 0.2” slit, representative of the available energy of the
spectrograph. Lab results have been confirmed by on-sky measurements and demonstrate
some gain in J (i.e., more than 40% for an optical seeing of 0.6”) and a strong increase (i.e.,
factor of ~2) of the fraction of energy available for the spectrometer in K and M band,
respectively (see Figure 21).
Figure 21: The fraction of energy available for the spectrograph in a 0.2" slit as a function
of the optical seeing is shown for the J (left) and K (right) band for NGS of V=10, 12, 16
mag and without AO correction. For reference, please consult the ETC.
For seeing >1.4”, the AO correction becomes very poor and unstable and will not result in
any improvement with respect to the NoAO mode. Therefore, AO observations are not
