CRIRES science data can be reduced using the ESO CRIRES pipeline. On Paranal, the quick-look pipeline makes an attempt to automatically reduce all science data. The reduction is performed using standard calibration solutions from a local calibration database which is refreshed every few months. Generally, any pipeline processing on the site is done on a best-effort basis. Its purpose is to offer a quick look to assess data quality etc.
At QC Garching, SCIENCE data are pipeline-reduced
using the best available calibration solutions (quality-checked and closest
in time, following the calibration cascade).
All settings are pipeline supported. The products of science reduction
are also quality-checked. If any irregularity in the reduced data is found,
an attempt is made to improve on this. If not possible, information about
the problem is made available in the data package. The policy is to never
CRIRES science data come in one format only: an exposure of a single echelle order with the 4x1 detector mosaic. Science observations can be differentiated whether the observing techniques nodding and jitter are applied.
Nodding: a spectrum is taken at telescope position A. Then, the telescope is moved along the direction of the slit to position B and another spectrum is taken. This is one nodding cycle AB. If further cycles are requested then another exposure is taken at position B before the telescope moves back to A. The complete sequence is ABBA. The next cycle would again start at position A, etc.
Jitter: Jittering is obtained by adding a small random offset in addition to the nodding offset.
Nodding and jittering and be combined. It is also possible to neither nod nor jitter. This makes four different observing techniques. In addition, special techniques using free offsets or a list of position angles are also offered:
The CRIRES calibration scheme, including SCIENCE data reduction, is shown here.
Recipe. All CRIRES science data are reduced using the pipeline recipe cires_spec_jitter. The recipe offers the following reduction steps: dark subtraction, correction for detector non-linearity, flat-fielding, image combination, spectrum extraction, wavelength calibration.
Dark subtraction. Subtraction of a dark exposure is only needed for the DIRECT observing technique. For NODDING, dark subtraction is automatically performed by subtracting A and B images. Science products in Service Mode packages have been dark-subtracted only in case of DIRECT.
Non-linearity. The CRIRES arrays show deviations from linearity for exposure levels above approximately 4000 ADUs. These deviations vary from pixel to pixel. They are determined by a dedicated set of flat exposures with increasing DIT (detector monitoring calibrations). For each pixel, the function ADU = A + B * DIT + C * DIT^2 is fit and the coefficients are stored in three images and packed into a fits cube. During science reduction, these coefficients are applied in order to correct the raw data.
Flat-fielding. Flat fields are used to correct for the blaze function and for fixed-pattern noise.
Image combination. In case of nodding observations, the individual exposures are combined after dark subtraction (if requested), correction for non-linearity, and flat-fielding have been applied.
Spectrum extraction. Spectra are extracted by a simple sum across the slit and by an optimal extraction technique. Both results are given in the output product.
Wavelength calibration. If a wavelength solution from an arc lamp or gas cell exposure is present then this result is applied for the wavelength calibration of the science data. Otherwise, the wavelength calibration is obtained from sky lines present in the science exposure. The latter is usually the case for settings above 2500 nm.
Products. We presently deliver the following types of SCIENCE products:
All products are fits files with four extensions. The primary header unit has an empty data section; each extension contains the results for the respective detector array.
All product file names follow a dedicated naming scheme.
CRIRES pipeline problems are documented under on the data package page.