Pipeline

AF2 pipeline

A new reduction pipeline for AF2/WYFFOS (AutoFib2/Wide Field Fibre Optical Spectrograph) is currently under development (the estimated time of release is October 1st, 2011). This software, written in IDL and soon publicly available, is able to perform full data reduction (including fibre to fibre sensitivity corrections and optimal extraction of the individual spectra) for a broad range of observing strategies. A quick-look version of the pipeline will also be available for carrying out real-time, preliminary reductions at the telescope while carrying out observations. This package is designed to be readily extensible to other fibre-fed spectrographs. These are its main features:

1. Graphical User Interface (GUI)

The user specifies the data files for an observation set including the calibration files via a GUI.
Data can be easily visualised and inspected with the IDL ATV package.
Quicklook option: an (even more) user-friendly, on-the-fly quicklook version of the pipeline will be available to observers so observing is all they have to worry about.

(Picture: Development version of the Graphical User Interface)

2. Automated data reduction

The software automatically subtracts a master bias, traces the fibres, performs flat-field correction and masks bad pixels in the science data.

(Picture: Diagram showing the process of the data reduction pipeline)

3. Extraction of spectra

An optimal extraction algorithm is used for extracting the spectra (a boxcar algorithm can optionally be used, e.g. for emission-line spectra).
The software accounts for wing emission from adjacent fibres.

(Picture: Each individual spectrum is extracted using the optimal extraction algorithm)

4. Wavelength calibration

The software selects an arc lamp spectrum from a fibre near the centre of the chip. The user is then prompted to identify the principle arc lines; other significant lines are automatically identified.
Upon userâ€™s approval, the dispersion solution is propagated to the rest of the fibres.

(Picture: Development version of the wavelength calibration procedure)

5. Sky subtraction

If some fibres were assigned to sky, a median sky spectrum is generated, scaled to the target fibre sensitivity, and subtracted from each science spectrum.
If, on the contrary, sky frames were taken by applying an offset to the telescope, the sky is subtracted on an individual fibre-to-fibre basis.

(Picture: Twilight sky flat giving the relative fibre-to-fibre sensitivity)

6. Output files

The pipeline generates fits files containing the base and sky subtracted spectra (with their associated uncertainties) transformed onto a common wavelength base.
The intensity is normalised according to the most recent measurement of fibre-to-fibre sensitivity.

(Picture: An example of the combined final spectrum (bottom) of a F star in the Ï‡ Per open cluster)