Quality Control and
Data Processing

BIAS

BIAS frames: uves_cal_mkmaster

DPR CATG = CALIB, DPR TYPE = BIAS

Raw BIAS frame for the 2 CCD

Purpose.
Bias frames are measured to monitor the status of the CCD camera. They come in stacks of 5 raw frames. They are routinely measured every night when FLAMES/UVES is operational. They are all processed into master_BIAS frames and quality-checked.

Recipe.
The pipeline recipe uves_cal_mkmaster determines median stacks of all input frames and produces a master BIAS frame.

QC checks.
The QC1 parameters median values, read noise and overall structure in the master BIAS are monitored.

Products.

product category (PRO CATG)	product number*
MASTER_BIAS	0000 (+0001)

* numbers in brackets refer to REDU CCD, others to REDL CCD.

FIBRE FLAT frames: flames_cal_prep_sff_ofpos

DPR CATG = CALIB, DPR TYPE = LAMP,FLAT,ODD-EVEN-ALL,OzPos-SimCal

All fibre flat field lamp frame (echelle orders from bottom to top, each order contains eight fibres) .

Purpose.
Fibre flat fields are taken with the calibration unit of the FLAMES fibre positioner and a flat field lamp. They come in three different varieties: with only ODD numbered fibres illuminated, with only EVEN numbered fibres illuminted, and with ALL fibres illuminated. Only science fibres are used; the SimCal fibre is dark. Fibre flats with DPR.TYPE=LAMP,FLAT,ODD,SimCal, etc. are intended to be used for science observations using simultaneous calibration. For other science observations, the OzPoz fibre flats are taken.
Three different types of fibre flat fields are needed because the images of the fibres on the detector partly overlap in the wings of the cross-dispersion profile in all-fibre flats. The recipe uses odd and even flats to determine the positions of all fibres and orders by making use of a Hough transform and stores the polynomial fit in the order definition table. A description of the Hough Transform and its application can be found in the article of Ballester (1994, Astron.Astrophys. 286, 1011).
The slit flat fields are equalised in the overlapping regions. A miminum set that covers the complete slit length used by the science observations is chosen as output. The odd/even fibre flats are normalised and cleaned for bad pixels. The fibre traces in the all-fibre flat are extracted and stored for relative normalisation between extracted science spectra from different fibres.

Recipe. i
The flames_cal_prep_sff_ofpos creates the final order defintion table with the positions of all fibres and orders, determines normalisation factors between the fibres and creates a minimum set of cleaned and normalised slit and fibre flats as input for the science reduction.

QC checks.
The pipeline recipe logs the absolute and relative transmission of every fibre. This is used to monitor the performance of the fibres (changes in transparency) and the stability of the flat field lamp .

Products.

product category (PRO CATG)	product number*	comments
FIB_FF_ODD_INFO_TAB	0000
FIB_FF_EVEN_INFO_TAB	0001
FIB_FF_ALL_INFO_TAB	0002
SLIT_FF_COM	0003 (+0016)	common data of slit flat field set
SLIT_FF_NOR	0004 (+0017)	normalisation data of slit flat field set
SLIT_FF_DTC	0005 (+0018)	data cube of nomalised slit flat field frames
SLIT_FF_SGC	0006 (+0019)	variances (data cube) for SLIT_FF_DTC
SLIT_FF_BPC	0007 (+0020)	bad-pixel mask (data cube) for SLIT_FF_DTC
SLIT_FF_BNC	0008 (+0021)	boundaries (data cube) for SLIT_FF_DTC
FIB_ORDEF_TABLE	0009 (+0022)	order definition table (final)
FIB_FF_COM	0010 (+0023)	common data of fibre flat field set
FIB_FF_NOR	0011 (+0024)	normalisation data from fibre flat fields
FIB_FF_NSG	0012 (+0025)	variance for FIB_FF_NOR
FIB_FF_DTC	0013 (+0026)	normalised, cleaned odd fibre flat fields (data cube)
FIB_FF_SGC	0014 (+0027)	variance for FIB_FF_DTC (data cube)
FIB_FF_BPC	0015 (+0028)	bad-pixel mask for FIB_FF_DTC (data cube)

* numbers in brackets refer to REDU CCD, others to REDL CCD.

FORMAT CHECK frames: flames_cal_predict

DPR CATG = CALIB, DPR TYPE = LAMP,FMTCHK,SimCal

Raw formatcheck frame (echelle orders from bottom to top)

Purpose.
Fibre formatcheck exposures are obtained with a ThAr arc lamp. The simultaneous claibration fibre is used to measure the positions of the calibration lines and to obtain a first-guess dispersion solution. This file is required for automatic pipeline processing only.
The geometric calibration of echelle spectra is a complete definition of the spectral format including the order position and the wavelength associated to each detector pixel. This step was traditionally carried out in echelle spectrographs via visual identification of a few lines. In order to predict the dispersion relation of UVES and to efficiently calibrate all possible optical configurations in an automatic way, many new methods had to be developed. The high non-linearity of the dispersion relation has made necessary to develop a physical model of dispersion. The precision with which the geometric calibration is performed determines the accuracy of all successive steps, in particular the optimal extraction and the photometric calibration.
The positions of a few hundred well separated ThAr lines contained in a reference table are predicted by the physical model and their central positions are projected onto the format-check frame.The lines are found in the narrow Th-Ar frame by a two-dimensional centering procedure. The initial dispersion relation, usually based on about a hundred initial detections is refined with successive iterations on the spectrum until most lines are found.

Recipe.
The pipeline recipe flames_cal_predict does a fit to the physical model to obtain a first guess solution for the dispersion. In principle it is also possible to perform an order tracing here, but this is achieved with a higher precision with order definition flats.
Guess line table. The guess line table is used downstream in the calibration cascade to achieve the final dispersion solution from ThAr lamp exposures. Although preliminary, this first guess line table is very important for the following steps since it replaces the interactive line selection traditionally done for echelle reduction.

QC checks.
The QC checks evaluate and monitor the differences between predicted and measured line positions, the shift against a reference frame, and the number of lines identified by the recipe. The figure below shows examples where differences in X position (dispersion direction) are plotted as a function of the position on the detector. The two left cases show a misalignment: the measured differences show a broad range of values without any structure. A good model prediction is indicated by a thin, well-clustered distirbution of the displayed points (right side).

Match and mismatch of physical model and format check frame. The normal result obtained after successful line matching (right) produces a well concentrated distribution with mean ordinate zero. A misalignment causes a failure of line matching (left). The two plots on top show examples for the upper CCD, the two others for the lower CCD.

The measured differences and shifts in X (dispersion) and Y (cross-dispersion) direction and the number of selected lines are stored in a database to monitor to detect changes of the spectral format.These can be due to shifts of the gratings/cross dispersers of the UVES spectrograph or can be caused by the fibre positioner. A destinction between both is only possible by comparing the results form UVES-MOS format checks with those from the UVES echelle mode

Products.

product category (PRO CATG)	product number*	comments
FIB_LIN_GUE	0003 (+0007)	(guess only)
FIB_ORD_GUE	0001 (+0005)	(guess only)
BACKGR_TABLE	0002 (+0006)	(guess only)

* numbers in brackets refer to REDU CCD, others to REDL CCD.

ORDER DEFINITION frames: flames_cal_orderpos

DPR CATG = CALIB, DPR TYPE = LAMP,ORDERDEF,SimCal

Raw order definition flat (echelle orders from bottom to top).

Purpose.
Fibre order definition flats are taken with the simultaneous calibration fibre and a continuum flat lamp. They are processed to find automatically the position of the SimCal fibre for each echelle order. This file is required for automatic pipeline processing only and is used by the slit flat field and fibre flat field recipes.
This kind of exposure provides an accurate position of the spectrum along the cross-dispersion direction. In this step the physical model uses the information on the instrument configuration provided in the FITS header of the raw frame to estimate the number of orders present in the image. Hough Transform detection is then applied to find the central position of each order and an estimate of their slope at the center. Finally, the cross-order profile is centered along the order and a polynomial fit is performed. A description of the Hough Transform and its application can be found in the article of Ballester (1994, Astron.Astrophys. 286, 1011).

Recipe.
The flames_cal_orderpos recipe processes the order definition flats. The positions are found through a Hough transform algorithm.

Products.

product category (PRO CATG)	product number*	comments
FIB_ORDERDEF	0000 (+0004)	splitted input frame
FIB_ORD_GUE	0001 (+0005)	order table (guess)
FIB_BKG_TABLE	0002 (+0006)

* numbers in brackets refer to REDU CCD, others to REDL CCD.

SLIT FLAT frames: flames_cal_mkmaster

DPR CATG = CALIB, DPR TYPE = LAMP,SFLAT

Flat lamp frame (echelle orders from bottom to top).

Purpose.
Slit flat field calibration frames are taken with a long slit and the continuum flat lamp. They measure fringing, fixed-pattern noise and the approximate blaze function. They are measured in three different slit positions with a stack of (typically) three frames at each position. The master slit flats are required for processing the fibre flats.

Recipe.
The flames_cal_mkmaster recipe uses the same algorithm as the uves_cal_mkmaster recipe. It creates, after bias subtraction, a median stack from all raw input frames of each slit position in order to reject statistical outliers due to e.g. cosmic ray events.

QC checks.
The flat field lamp efficiency and stability are checked.

Products.

product category (PRO CATG)	product number*	comments
MASTER_SFLAT	0000-1-2 (+0003-4-5)	slit pos1-2-3

* numbers in brackets refer to REDU CCD, others to REDL CCD.

FLAMES Wavelength calibration frames: uves_cal_wavecal

DPR CATG = CALIB, DPR TYPE = LAMP,WAVE.OzPos-SimCal

Wavelength calibration frame (echelle orders from bottom to top).

Purpose.
Wavelength calibration frames are taken with the calibration unit of the FLAMES fibre positioner and a ThAr arc lamp. They are used to find the final dispersion relation for each fibre. Arc lamp frames with DPR.TYPE=LAMP,WAVE,SimCal are intended to be used for science observations using simultaneous calibration. For other science observations, the OzPoz WAVEs are taken.
Recipe.

The flames_cal_wavecal recipe has been build around the uves_cal_wavecal algorithm. It uses the first-guess linetable and the final order table (see FFLAT recipe) to find the strongest lines in the arc frame for every fibre. Then the reference linetable is used to match the fainter lines from which the dispersion relation is determined.

QC checks.
The QC check evaluates the distribution of resolving power R over the detector for one fibre, the mean resolution per fibre, the distribution of the fit residuals and the distribution of the selected lines across the detector. Median and mean values of R and the line FWHM, the standard deviation of the dispersion solution, and the numbers of identified and selected lines are stored in a database.

Products.

product category (PRO CATG)	product number*
FIB_LINE_TABLE	000r20 (+0004)

* numbers in brackets refer to REDU CCD, others to REDL CCD.