FLAMES/GIRAFFE pipeline:
CALIB recipes

DPR.CATG = CALIB, DPR.TYPE = BIAS

Raw BIAS frame

Purpose. Bias frames are measured to monitor the status of the CCD. They come in stacks of 5 raw frames. They are routinely measured every night when GIRAFFE is operational. They are all processed into master_BIAS frames and quality-checked on the mountain and by QC Garching.

Recipe. The pipeline recipe gimasterbias processes GIRAFFE BIAS frames. These are combined and median-stacked.

QC checks. The pipeline measures median values, read noise and global structure in the master BIAS and in the first raw frame.

Trending. Click here for results of the BIAS trending.

Products:

* coded as HIERARCH.ESO.PRO.CATG in the fits header
** index of the PIPEFILE name, coded as PIPEFILE in the fits header
*** used in the delivered name

DPR.CATG = CALIB, DPR.TYPE = DARK

Purpose. Dark frames are measured to monitor the status of the CCD. They come in stacks of 3 raw frames, each with 3600 sec integration time. They are taken about monthly. They are processed into master_DARK frames and quality-checked by QC Garching.

Recipe. The pipeline recipe gimasterdark processes GIRAFFE DARK frames. These are combined and median-stacked.

QC checks. The pipeline measures median values and dark current in the master DARK frame.

Trending. Click here for results of the DARK trending.

Products:

* coded as HIERARCH.ESO.PRO.CATG in the fits header
** index of the PIPEFILE name, coded as PIPEFILE in the fits header
*** used in the delivered name

DPR.CATG = CALIB, DPR.TYPE = LAMP,FLAT or LAMP,FLAT,NASMYTH

Raw FLAT frame

Purpose. Flat frames are normally illuminated by the calibration unit on OzPoz, with the lamp moved across the fibres which are arranged in a spiral pattern ('robotic flats'). While this is a good approach for the Medusa and IFU fibres, the Argus fibres are not well illuminated by this procedure. Therefore, there are also Argus flats taken on the illuminated Nasmyth screen ('nasmyth flats').

The flats measure fixed-pattern noise (pixel-to-pixel sensitivity variations), fibre signal localization and width, relative transmission (fibre-to-fibre), fringing (in the red), and the approximate response function. Normally 3 flats are measured.

Recipe. The pipeline recipe gimasterflat processes GIRAFFE FLAT frames. The input raw frames (typically three) are debiased, combined, median-stacked and normalized to 1 sec. Next all fibres are localized by a profile fit in the course of the optimal extraction procedure and extracted. Finally they are normalized such that the signal from the fibre with the highest transmission is set to one, and all other fibres are normalized relative to that fibre. In the normalization procedure, all SIMCAL fibres are neglected, as well as the SKY fibres for the IFU and Argus slits. The product files have one column per extracted fibre, plus a binary table as extension, the fibre_setup table which is described here. Only localized and extracted fibres get a column in the products, not any "missing" fibres (both non-allocatable and non-allocated ones).

QC checks. The pipeline measures median/mean and rms of the following parameters: relative fibre transmission; fibre signal curvature; signal width, and the flat-field lamp efficiency.

Trending. Click here for the FLAT trending. The lamp efficiency and the average flat level is trended.

Products:

* coded as HIERARCH.ESO.PRO.CATG in the fits header
** index of the PIPEFILE name, coded as PIPEFILE in the fits header
*** used in the delivered name

The error file (PRO.CATG = FF_EXTERRORS) contains the calculated standard deviation per pixel of the FF_EXTSPECTRA file (containing: photon noise, read noise).

Products of the Nasmyth flats have similar pro.catg values (with FF replaced by NF), and somewhat different product codes which are listed here.

Relative fibre transmission. An important property of the Giraffe fibres is the stability of their relative transmission, since the SKY signal can only be recorded in dedicated (IFU and Argus) or user-selected (Medusa) fibres. The level of precision of sky subtraction is therefore limited by the accuracy of the relative fibre transmission as recorded by the flats. The following figure demonstrates that the sky signal can be measured with a precision of much better than 1% for most of the fibres.

Stability of relative fibre transmission: transmission values (normalized to a mean value of 1) from 94 days of Medusa1 flats are plotted on top. The residual scatter is plotted below, with the two broken lines marking 1% and 3% rms, respectively. Most fibres have a transmission stable at the 0.3 % level over about 100 days.

Illumination. While Medusa and IFU flats are sufficiently uniform when obtained with the robotic lamp, the Argus fibres are not completely illuminated by the robotic calibration lamp. The differences between a 'robotic' Argus flat and a Nasmyth flat are shown below.

An Argus Nasmyth flat (below) and a robotic flat (top). The extracted spectrum has been collapsed in dispersion direction, to display the fibre-to-fibre efficiency variation and the illumination differences. The spikes are due to SKY fibres (15 in total), and SIMCAL fibres (5 in total). The robotic flat has strong ilumination artefacts (the deep vertical triangles) which would propagate into the science data if used for flat-fielding. The Nasmyth flat has a much more uniform illumination which makes it a much better choice for science flat-fielding.

The next figure compares a Nasmyth flat and a sky flat. The sky flat has been taken in twilight conditions on the sky and avoids all residual illumination artefacts which could degrade the Nasmyth flat.

Comparison of a sky flat (red) and a Nasmyth flat (black). No residual illumination effects are visible. In particular, the spikes of width 2-3 fibres, and the degraded transmission at the end, are a real effect and not caused by the Nasmyth illumination.

This figure demonstrates that Argus data can be reliably flattened with the Nasmyth flats.

This is also evident from the following figure which compares the non-flattened skyflat (below) and the skyflat after flattening with the nasmyth flat (top). The bumps and wiggles have disappeared, and the residual transmission differences are about 2.4% rms.

Comparison of extracted but not flat-fielded sky_flat (below), and the sky_flat flattened with the Nasmyth flat (top).

DPR.CATG = CALIB, DPR.TYPE = LAMP,WAVE

Raw WAVE frame (right: closeup to display single emission lines from single fibres)

Purpose. WAVE frames are illuminated by the arclamp calibration unit on OzPoz, with the lamp moved across the fibres which are arranged in a spiral pattern.

The arclamp frames are used to derive the global dispersion solution for science (and STD) frames.

Recipe. The pipeline recipe giwavecalibration processes GIRAFFE WAVE frames. The input raw frame is debiased. The corresponding localization (PLOC) and width (PWID) solutions from the gimasterflat recipe are used to localize and extract the fibre signals. The line catalog is searched for matching emission lines which are then identified in the fibre signals. Blended, saturated and too faint lines are rejected, as well as lines with a non-Gaussian PSF. The Giraffe optical model is globally fitted. The residuals between that solution and the positions of the identified emission lines are fitted by a 2D Chebychev polynomial to obtain the complete dispersion solution. Small fibre-to-fibre differences are taken into account by the static slit geometry setup table and the grating table. The extracted arclamp frame is finally wavelength calibrated and rebinned, to deliver a product suitable for quality control checks.

Extracted arclamp frame (left) and rebinned arclamp frame (right); each extracted fibre contributes to the global pattern which should give a straight line for each emission line. The straightness of the emission lines is a sensitive check on the precision of the dispersion solution. These files are therefore delivered to the SM user although they are not required for reduction of SCIENCE frames.

QC checks. The pipeline measures the mean flux level of the raw input frame, the number of saturated pixels, the calibration lamp efficiency, the rms of the dispersion solution, the number of lines found, accepted, and used for the fit.

Trending. Click here for the trending of the wavelength solution, and here for the calibration lamp trending.

Products:

* coded as HIERARCH.ESO.PRO.CATG in the fits header
** index of the PIPEFILE name, coded as PIPEFILE in the fits header
*** used in the delivered name

The error file (PRO.CATG = ARC_EXTERRORS and ARC_RBNERRORS) contains the calculated standard deviation per pixel of the ARC_EXTSPECTRA file (containing: photon noise, read noise).

DPR.CATG = CALIB, DPR.TYPE = STD

Purpose. Flux STD frames are regularly taken only for ARGUS observations. They can be used for response correction and flux calibration. They are usually followed by three Nasmyth flat exposures. For efficiency monitoring, there is also a dedicated set of Argus settings taken about once a month.

Recipe. The gistandard recipe processes the flux STD data just like the science data, with the additional final step of extracting a response curve and an efficiency curve. The products are delivered in the Service Mode packages. Their PRO.CATG keyword is the same as for science products, with the string SCIENCE replaced by STD. The user may want to use the response curve and perform a flux calibration of the science data.

QC checks. Checks are done for over and under-exposure (some of the STD targets have high proper motions and may have escaped from proper acqusition in the past).

Trending. The results from the standard set of STD data taking about monthly (system efficiency) are available here.

Products.

* coded as HIERARCH.ESO.PRO.CATG in the fits header
** index of the PIPEFILE name, coded as PIPEFILE in the fits header
*** used in the delivered name

The error file (PRO.CATG = ARC_RBNERRORS) contains the calculated standard deviation per pixel of the ARC_RBNSPECTRA file (containing: photon noise, read noise). This error is propagated to the error file of the recombined spectro-image, STD_RCERRORS.