CRIRES User Manual
Doc. Number: ESO-254264
Doc. Version: P109.4
Issued on:
2021-12-01
Page:
16 of 99
Document Classification: ESO Internal Use [Confidential for Non-ESO Staff]
positions of the cross-disperser grating and Echelle grating and refining further via the use
of a piezo driven tip-tilt mirror that has actuators aligned with the main- and cross-dispersion
axes.
This is an iterative process which may take a few minutes, the exact duration depends upon
the unpredictable behaviour of the cross-disperser grating and Echelle grating functions.
The metrology then ensures that these emission lines are indeed located at their fiducial
positions on the science FPA before any science exposure (or any calibration exposure
when used during daytime) follows. Those science/calibration exposures obtained after a
successful application of metrology will have the following metrology keywords written to
their headers (values below are examples):
HIERARCH ESO OCS MTRLGY DX = 0.002 / [pixels] Final mean x residual relative to fiducial
HIERARCH ESO OCS MTRLGY DY = 0.039 / [pixels] Final mean y residual relative to fiducial
HIERARCH ESO OCS MTRLGY NITER = 5 / Total number of iterations performed
HIERARCH ESO OCS MTRLGY ST = T / Success or failure of metrology
HIERARCH ESO OCS MTRLGY TOTDX = -1.430 / [pixels] Average total applied correction in the main
dispersion direction
HIERARCH ESO OCS MTRLGY TOTDY = 0.194 / [pixels] Average total applied correction in the cross-
dispersion direction
The metrology can be activated or deactivated in the acquisition and observing templates.
When it is enabled during the acquisition, the metrology runs in parallel to the telescope
preset, therefore no overheads are associated to the metrology (see Section 5.6).
3.2 The Warm Part
The Warm Part of CRIRES consists of different subsystems (see Figure 8
for an overview):
the AO Unit, the Calibration Unit which also includes a Fabry-Perot Etalon System and a
carriage stage with the new Polarimetry Unit and new sources for wavelength calibration
described in detail in Section 3.2.3.
3.2.1 The Adaptive Optic System MACAO
The adaptive optics system of CRIRES is described in Paufiqué et al. (2004, SPIE 5490,
216). The multi-application curvature adaptive optics system (MACAO) for CRIRES corrects
a turbulent wavefront and provides diffraction limited images at the focal plane. The overall
sensitivity is thereby improved by about a factor two for point-sources. To highlight the
advantage of combining MACAO and CRIRES a PSF is shown in Figure 9
in AO open loop
(uncorrected) and closed loop, where the PSF is reconstructed from wavefront
measurements. The non-circular PSF in open loop is due to the very short integration time
used.
The following section provides an introduction to the field of adaptive optics and
atmospheric turbulence, and essentially is taken from the NACO user manual. For further
reading, see for example: “Adaptive optics in astronomy”, Rodier 1999, Cambridge
University Press, or “Introduction to adaptive optics”, Tyson 2000, Bellingham/SPIE.
