User Manual
Doc. Number: ESO-323064
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·
Position angle
(TSF:
INS.DROT.POSANG
) determines the position angle (PA) of the
slit when the SKY derotator mode is selected. The PA is counted from North (i.e., PA=0
deg) via East.
·
Gas cell
(TSF:
INS.OPTI1.NAME
) sets the name of the optical gas cell to be used
during the science. The default value (FREE) should be set for observations without any
gas cell, while GAS_SGC
or GAS_N2O should be set for observations at short (i.e., YJHK)
and long (i.e., LM) wavelength, respectively. Gas cells provide for simultaneous wavelength
calibration by imprinting the absorption spectrum of the gas onto the spectrum of the target.
Note: the option of using the gas cell is only available for spectroscopic mode, but not for
polarimetry.
6.3.2 Science templates
The science observation template sets the instrument, if different from the acquisition, as
well as the detector integration time (DIT) and the number of individual integrations
averaged to create an exposure (NDIT). In addition, it defines the number of exposures to
be taken in different positions for background subtraction purpose.
As mentioned in §5.2.5.1, the most common observing technique suited for point-source
like targets is the nodding along the slit, where the target is always kept along the slit (i.e.,
no off-slit exposures are possible) and the sky signal is removed from the object spectrum
by subtracting two exposures taken at different slit positions.
On the other hand, when the target is an extended object nodding along the slit is no longer
a viable strategy because removing the sky signal from the object spectrum requires
necessarily to take exposures off-slit (not yet offered in P108).
In addition, CRIRES offers the possibility of using the spectro-astrometry technique (not yet
offered in P108) to obtain very high spatial and spectral resolution line imaging (Beckers,
J., 1982, Opt. Acta, 29, 361; Bailey, J., 1998, MNRAS 301, 161 and references therein).
First results using this technique with the old CRIRES are described in Pontoppidan et al.
2008. Note that this technique requires the target being also the SVGS, whereas the NGS
can be different.
Table 9: Overview of the available CRIRES spectroscopic observing templates. (*)
Templates not offered in P108
INSTRUMENT MODE
TEMPLATE NAME
COMMENT
Spectroscopy
CRIRES_spec_obs_AutoNodOnSlit
Exposures are taken only by
nodding the target along the
slit. Off-slit exposures are
not
possible
(i.e.,
recommended for point
sources)
(CRIRES_spec_obs_GenericOffset*)
Exposures can be taken
along and/or off the slit,
depending on the user
defined
offsets
(i.e.,
recommended for extended
object)
