User Manual
Doc. Number: ESO-323064
Doc. Version: 2
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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, whereas by the detector performance from Y, J and H bands. In the thermal
background regime, observations benefit from the high resolving power of CRIRES as
telluric features are better removed compared to spectrographs at lower resolution.
Based on data collected during the first and second on-sky commissioning runs, as well as
in the integration hall in Garching:
•
Spectral resolution of ~40,000 and ~80,000 can be achieved with slit wi
dth 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 <0.3px 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 close 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” sl
it, 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 20).
Figure 20: 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.