The QC group processes a stream of
science-grade data products for selected VLT instruments. They are created using certified pipelines and certified master calibrations.
Find an overview of the current streams here.
For some instruments, science-grade data products are created by QC Garching, using certified pipelines. Currently these are 1D spectral data products from UVES (Echelle mode), XSHOOTER (Echelle mode), and GIRAFFE (Medusa MOS modes). See the QC pages for those instruments for more information.
Since 2013, more than 100,000 science-grade flux-calibrated 1D data products are available covering the entire data history of UVES Echelle mode, incl. SLICER mode. New data are added on a monthly basis; data products older than one year are freely accessible, younger data products are available to PIs. More ...
Find the phase3 spectral archive interface here.
The UVES pipeline is designed to reduce raw SCIENCE spectra taken in Echelle mode to a level almost free from instrumental signature. Formally, there are two pipelines: the UVES-Echelle pipeline, and the FLAMES/UVES (or UVES MOS) pipeline. The UVES-Echelle pipeline is described here. The UVES MOS pipeline is handled here.
On Paranal, the quick-look pipeline makes an attempt to automatically reduce all science data taken in Echelle and MOS modes. The reduction is performed using standard calibration solutions from a local calibration database which is refreshed every now and then. All settings are supported. Furthermore, for non-standard wavelength settings used in Visitor Mode, a complete set of calibration files is acquired and processed in order to obtain solutions. This often works fine, but since the number of possible non-standard UVES configurations is very high, there is poor experience with the pipeline behaviour in some of these cases. Generally any pipeline processing on the site is done on a best-effort basis.
slit acquisition image (observed before 2002-11-23)
ACQUISITION
SLIT
slit acquisition image
*The destinction between point-like and extended sources is made by the user during the Phase 2 proposal.
Raw science data are usually accompanied by slit viewing images.
Recipe. A science raw file is pipeline-processed by the pipeline recipe uves_obs_scired. Data are corrected for bias, interorder background, sky background, sky emission lines and cosmic ray hits. They are flattened, optimally extracted and finally merged. A response correction is also performed if an appropriate response curve exists for the setting. Find here a detailed record of the reduction steps.
Extraction. The UVES pipeline knows three extraction modes:
optimum (OPT)
average (AVG)
two-dimensional (2D)
Optimum extraction is the default extraction mode for "ECHELLE" and "ECHELLE,ABSORPTION-CELL" observations; average extraction for "ECHELLE,SLICER" and "ECHELLE,ABSORPTION-CELL,SLICER" observations. A two-dimensional extraction is performed if the DPR TYPE keyword is "OBJECT,EXTENDED".
Optimum extraction provides an optimized signal-to-noise ratio and is suitable for point sources. Average extraction is an alternative mode which simply averages any signal along the slit and above the sky background level. It may be a good choice in case of failure of the optimum extraction, e.g. at high exposure level. Two-dimensional extraction actually does not extract the signal at all, but provides a flattened and wavelength-calibrated solution with the flux redistributed into wavelength-slit coordinate space. This means that any spatial information along the slit is preserved and can be manually extracted later. Find more information here..
Optimum extraction. In optimal extraction mode (OPT) the UVES pipeline assumes a Gaussian profile for the cross-dispersion flux distribution.
This procedure:
yields optimum S/N,
automatically discriminates against any non-Gaussian components in the cross-dispersion profile.
This means specifically:
automatic sky subtraction (since the sky background is treated as a pedestal),
automatic cosmic ray rejection (whenever the hit has a non-Gaussian distribution),
automatic sky emission line removal (since these fill up the whole slit and have a rectangular profile).
The spectra are then flattened in order-bin space, i.e. with extracted flats. Flat extraction is done with the weight factors derived from the science spectrum.
The UVES pipeline also offers flattening in pixel space (the science spectrum is divided by the flat field before extraction). Checks done on high-S/N, featureless spectra show that the pixel-space flattening may yield slightly (less than 10%) higher S/N than extracted flattening. However, telluric lines in the flats are found to propagate much stronger into the extracted science spectrum in the case of pixel-space flattening. Since telluric lines in the flats fill the whole slit, they are effectively removed by the optimum extraction.
Flattening corrects for the blaze function within the orders. In the red settings (860 nm), flattening also efficiently removes fringing.
A response correction (flux calibration) can be applied to the extracted spectra. This additional step can be performed for all settings with master response curves (i.e. the standard settings). Check out for more information and downloads here.
In principal any instrument response curve derived from a recent STD star spectrum can also be used for flux calibration. The difference between those "individual" response curves and the master response curves is the critical compilation of the latter ones, and the averaging of many individual ones into the master. In any case it should be clear that UVES cannot provide anything better than a relative flux calibration, mainly due to the slit losses and due to the observations taken under uncontrolled photometric conditions.
Products.
The following reduction products per CCD (i.e. 1 BLUE for the blue arm, 1 REDLower and 1 REDUpper for the red arm) are created by the pipeline, if flux calibration is provided:
product category (PRO CATG)
product number*
format
comments
RED_SCI_POINT or RED_SCI_EXTENDED
0000 (+0013)
1D (wavelength space)
final science spectrum (RV corrections to heliocentric and barycentric scale are provided in FITS header)
ERRORBAR_SCI_POINT or ERRORBAR_SCI_EXTENDED
0005 (+0018)
1D (wavelength space)
errorbar file** corresponding to RED_SCI (contains the standard deviation of the extraction as error estimate for the extraction procedure)
ORDER_TRACE
0008 (+0021)
tfits table
position and FWHM information per order
CRMASK
0009 (+0022)
tfits table
cosmic ray mask table
FLUXCAL_SCIENCE
0011 (+0024)
1D (wavelength space)
flux-calibrated science spectrum (in 10E-16 erg/s/cm**2/A)
FLUXCAL_ERRORBAR
0012 (+0025)
1D (wavelength space)
errorbar file corresponding to FLUXCAL_SCIENCE
* The numbers in brackets refer to REDU CCD, others to BLUE or REDL.
** defined by the variance of the chi-square fit to the signal obtained during optimum extraction. The error is determined by the boundary of the chi ... chi+1 domain. The errorbar file then gives the size of the bar which is symmetrical around the most likely value.
If flux calibration is not provided:
product category (PRO CATG)
product number*
format
comments
RED_SCI_POINT or RED_SCI_EXTENDED
0000 (+0011)
1D (wavelength space)
final science spectrum (RV corrections to heliocentric and barycentric scale are provided in FITS header)
ERRORBAR_SCI_POINT or ERRORBAR_SCI_EXTENDED
0005 (+0016)
1D (wavelength space)
errorbar file** corresponding to RED_SCI (contains the standard deviation of the extraction as error estimate for the extraction procedure)
ORDER_TRACE
0008 (+0019)
tfits table
position and FWHM information per order
CRMASK
0009 (+0020)
tfits table
cosmic ray mask table
* The numbers in brackets refer to REDU CCD, others to BLUE or REDL.
** defined by the variance of the chi-square fit to the signal obtained during optimum extraction. The error is determined by the boundary of the chi ... chi+1 domain. The errorbar file then gives the size of the bar which is symmetrical around the most likely value.
For slicer observations reduced with average extraction:
product category (PRO CATG)
product number*
format
comments
RED_SCIENCE_SLICER
0000 (+0010)
1D (wavelength space)
final science spectrum (RV corrections to heliocentric and barycentric scale are provided in FITS header)
ERRORBAR_SCIENCE_SLICER
0005 (+0015)
1D (wavelength space)
errorbar file corresponding to RED_SCIENCE (contains the standard deviation of the extraction as error estimate for the extraction procedure)
FLUXCAL_SCIENCE
0008 (+0018)
1D (wavelength space)
flux-calibrated science spectrum (in 10E-16 erg/s/cm**2/A)
FLUXCAL_ERRORBAR
0009 (+0019)
1D (wavelength space)
errorbar file corresponding to FLUXCAL_SCIENCE
* The numbers in brackets refer to REDU CCD, others to BLUE or REDL.
For slicer observations without flux-calibration:
product category (PRO CATG)
product number*
format
comments
RED_SCIENCE_SLICER
0000 (+0008)
1D (wavelength space)
final science spectrum (RV corrections to heliocentric and barycentric scale are provided in FITS header)
ERRORBAR_SCIENCE_SLICER
0005 (+0013)
1D (wavelength space)
errorbar file corresponding to RED_SCIENCE (contains the standard deviation of the extraction as error estimate for the extraction procedure)
* The numbers in brackets refer to REDU CCD, others to BLUE or REDL.
*The destinction between point-like and extended sources is made by the user during the Phase 2 proposal.
Raw science data are usually accompanied by slit viewing images.
mirror sites:
PL (internal link)
HQ
[?]
Science Reduction
