CRIRES User Manual
Doc. Number: ESO-254264
Doc. Version: P109.4
Issued on:
2021-12-01
Page:
60 of 99
Document Classification: ESO Internal Use [Confidential for Non-ESO Staff]
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The slit viewer guide star (SVGS): it is point-like source used for fine guiding using
the SV camera in one of the 3 passbands, J, H or K.
•
The AO natural guide star (NGS): when the AO correction is required, the NGS can
be a point-like source or an extended object. In terms of wavelength, only its R band
magnitude and B-R colour difference are relevant. (Note that for spectro-polarimetry
and for spectro-astrometry, the NGS must be the target).
In general, the sequence of the events taking place during the execution of the acquisition
templates can be summarized as follows:
1. Telescope presets to the target position;; a guide star in the FoV of the telescope is
selected for telescope guiding and to correct the M1 mirror shape (active optics, not
to be confused with adaptive optics = AO)
2. In NGS mode, the telescope moves then to the AO NGS specified by the user. Once
the AO NGS is centred on the MACAO field selector, the AO loop is closed.
3. The telescope moves to the SVGS, which is then acquired and centred before
starting the secondary guiding.
4. At this point the AO loop is closed (if AO mode) and the guiding is active, therefore
the telescope offsets to the target, which is manually centred on the slit.
It should be noted that the instrument setup (i.e., desired wavelength setting, slit width,
polarimetry optical element and metrology system if requested) is performed automatically
during the acquisition. Table 10 summarises the list of available acquisition templates.
Table 10: Summary of available CRIRES acquisition templates
INSTRUMENT
MODE
TEMPLATE NAME
COMMENT
Spectroscopy
CRIRES_spec_acq_NGS
AO assisted spectroscopy
CRIRES_spec_acq_NoAO
Seeing limited spectroscopy
CRIRES_spec_acq_NGS_difftrack
AO assisted spectroscopy with
differential tracking
CRIRES_spec_acq_NoAO_difftrack
Seeing limited spectroscopy
with differential tracking
Polarimetry
CRIRES_pol_acq_NGS
AO assisted polarimetry
CRIRES_pol_acq_NoAO
Seeing limited polarimetry
