Recipe. A science raw file is pipeline-processed by the pipeline
recipe flames_obs_scired. The
bias level and the interorder background are subtracted. Every order of
the spectrum is extracted, flat-fielded, de-convolved for fibre cross talk,
wavelength calibrated, and corrected for differences in fibre transparency.
Finally, the orders are merged.
Extraction. The UVES-MOS pipeline knows two extraction modes:
- optimum (OPT)
- average (AVG)
Optimum extraction is the default extraction mode. It provides
an optimized signal-to-noise ratio. Average (or standard) 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.
Optimum extraction. The 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
- automatic cosmic ray rejection (whenever the hit has a non-Gaussian
- automatic sky emission line removal (since these fill up the whole
slit and have a rectangular profile).
calibration. UVES-MOS offers the possibility
to use one fibre for measuring a ThAr spectrum simultaneously with the
science observations. The science recipe cross-correlates the
simultaneous ThAr spectrum with a template spectrum and determines a
velocity shift of the observation with respect to the template. The same
calculation is performed with the day-time ThAr calibration.
The cross-correlation is calculated on each order separately. The results
are written in the CORVEL_TAB file. The average velocity shift (in km/s)
with respect to the template is written in the QC.CCF.POSAVG header keyword;
QC.CCF.POSRMS contains the rms of the average and QC.CCF.POSOFF the shift
of the day-time ThAr spectrum with respect to the template.
Products. These are the reduction
- one FIB_SCI_INFO_TAB tfits table containing information about the fibre
- one MWXB_SCI file per CCD (i.e. two files); this is the merged and
wavelength-calibrated extracted spectrum that has been corrected for
different throughputs of the fibres; it is a 2D image with wavelength
on x-axis and fibre on y-axis
- one ERR_MWXB_SCI file per CCD; this is the errorbar file corresponding
- one XB_SCI file per CCD; this is a 3D data cube containing the extracted
and throughput-corrected spectrum for each order
- one MWXB_SCI_RAW file per CCD; similar to MWXB_SCI but without correction
for fibre throughput
- one ERR_MWXB_SCI_RAW file per CCD; the corresponding errorbar file
- one XB_SCI_RAW per CCD; extracted and not throughput-corrected spectra
for each order
- in case of SimCal data, one CORVEL_TAB table per CCD containing the
results of the cross-correlation.