The GTC/OSIRIS Data Reduction System
1

1Alessandro Ederoclite , Jordi Cepa
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Instituto de Astrofı́sica de Canarias, C/Via Lactea S/N, La Laguna, Tenerife, Spain

Abstract
I present the online and the offline data reduction system for OSIRIS, the optical multi-mode instrument for GranTeCan. The software is written in Python and invokes PyRAF tasks which have been optimized for theinstrument. I review the characteristics of the intrument and of the software. I will also present the improvements which are foreseen for both the instrument and the software. The flexibility of the software makes it easy tobe adapted to other telescopes/instruments.

Gran Telescopio Canarias (GTC)
Figure 2 The instrument OSIRIS
attached at the Nasmith focus of
GTC and the first author of theposter during commissioning.

Located in the Observatorio de Roque de losMuchachos, in the Island of La Palma (CanaryIslands, Spain), GTC is an alt-azimuthal telescope. Its primary mirror is made of 36 hexagonal segments (of a diameter of 1.9m each)building up a 11.3m quasi-hexagonal primarymirror (equivalent to a circular aperture of 10.4m).
Figure 1 The primary mirror of GTC. M2 canbe seen reflected in M1 while M3 is in the buffer
emerging from M1. The four “folded Cassegrain”
focal stations are all located in the upper half ofthe black ring surrounding M1.
The “Nasmyth B” focus, where OSIRIS is located,is on the right side of this picture.

The OOPS: OSIRIS Offline Pipeline Software.
The OOPS has been designed to fully support all the observing modes of OSIRIS (although v1.0 only supports broad–band imaging, tunable filter imaging and long–slit spectroscopy). It is fully customisable and the user can do all the reduction step-by-step.
The OOPS is a Python script executing PyRAF tasks. All PyRAF tasks can be tuned and theparameters are stored in a file for future use or to be used in the OQuLTo software.
The User must define the directories where the raw data is stored, where the reduced datais stored and where the “intermediate” data (i.e. the frames at intermediate steps of thereduction process) is stored. Whenever a task is called, the OOPS checks that the required
calibration data exists and that the execution of such a task does not overwrite an alreadyexisting file. The OOPS also checks that a user does not combine images which have beentaken with different modes of the CCD or different optical elements in the optical path (ifapplicable).

OSIRISOSIRIS (Optical System for Imaging and low Resolution Integrated Spectroscopy) is the
optical Day–One instrument for GTC. OSIRIS is equipped with a mosaic of two backilluminated 2048×4096 CCDs. The field of view of OSIRIS is 8.53’ × 8.53’ in direct
imaging and 8.0’ ×5.0’ in spectroscopy.
Its basic modes are:
• Imaging– Broad-band imaging; using Sloan filters– Tunable-filter imaging∗ Standard TF Imaging; using a red (600-1000nm) or a blue (375-675nm) TF which
can be tuned to have a FWHM of ∼1.2 – 2.0nm (depending on wavelength)∗ Straddling line; combining TF with charge shuffling to observe a line and its blue andred continuum∗ N-shuffle; combining TF with charge shuffling to scan through a wavelength range• Spectroscopy– Long-slit spectroscopy; standard long slit spectroscopy with resolution (λ /δ λ ) between 300 and 2500
– Multi-Object Spectroscopy (MOS)∗ Standard MOS∗ Nod-and-shuffle; shuffling the charge when moving the telescope to a blank field for
improved background subtraction∗ micro-shuffle; shuffling the charge when moving the telescope to a blank field for
improved background subtraction in a crowded field (uses a pinhole mask instead of
the standard MOS-mask)• Fast-modes

Figure 3 The OOPS running.

– Fast photometry∗ Decentered slit; uses charge shuffling taking an image through a 3” slit at the top ofthe mosaic∗ Windowing with frame transfer; readout time of a small window can be as low as 0.2s
– Fast spectroscopy∗ Decentered slit; uses charge shuffling taking spectra through a custom-made MOS
mask with only one aperture at the top of the mosaic∗ Frame transfer; uses a customised MOS mask with a small slit centered at 1/4 of thedetector edge. The spectrum is then transferred to the non-illuminated part of thedetector and read out while a new spectrum is being observed.

Towards OOPS and OQuLTo v2.0OQuLTo: OSIRIS Quick Look Tool

The planned improvements for the softwares are:OQuLTo is the online software that can be used for real–time assessment of the quality ofthe data. OQuLTo is a set of scripts:• Data analysis included in OOPS

• startOQuLTo.py starts up the scheduler• onlinepipeline.py is the scheduler: checks every 5 seconds if every file in the raw data
directory has been reduced and, if needed, it starts the reduction, calling IRAFpipeline.py• IRAFpipeline.py is the actual pipeline which reduces the images depending on theirheader keywords• stopOQuLTo.py stops the scheduler and saves the log
OQuLTo only needs two configuration files: one with the IRAF parameters to be used (normally using a copy of the one used by OOPS) and one with the name of the directories where
the raw data is placed and where the reduced data will be placed.
If a calibration frame does not exist, the software uses a temporary solution (informing theUser about this). In case, for example, a proper bias for a science exposure does not exist,
the software only uses the overscan region. In another, potentially common, case, if a flat
field is not available, the software does a low–order fit to the image and uses it as a flat. At
the end of the reduction process, OQuLTo re–builds the multi–extension fits file.
OQuLTo can also work “offline” reducing, in alphabetical order, all the data which ispresent in a directory.

• Support of MOS and fast modes• Abort the execution of a task in OOPS
• GUI for OQuLTo
Tentatively a version 1.0 will be available on 1st Nov 2009 and a version 1.5 (supportingall modes) will be available on 1st Feb 2010. Version 2.0 (with a revised architecture of thesoftware) will be released on 1st Sep 2010.
OOPS and OQuLTo will be extensively used during the OTELO survey (Cepa et al 2008).
The simplicity and the versatility of OOPS and OQuLTo make them ideal to be adapted to asimilar instrument (i.e. any multi–mode instrument in the optical).

References:
Cepa, J. et al. 2008 A&A, 490, 1
Cepa, J. et al. 2009, A&A, in prep.
All the pictures in this poster belong to the author (A.Ederoclite, 2008)
This work was funded by the Spanish MICINN under the Consolider-Ingenio 2010 Program grant CSD200600070: First Science with the GTC