Data Reduction and Handling for SPHERE

Astronomical Data Analysis Software and Systems XVII c 2008 ASP Conference Series, Vol. 394, R. W. Argyle, P. S. Bunclark, and J. R. Lewis, eds.

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Data Reduction and Handling for SPHERE A. Pavlov, M. Feldt, Th. Henning Max Planck Institut f¨ ur Astronomie, K¨ onigstuhl 17, Heidelberg, 69117, Germany SPHERE team Laboratoire d’Astrophysique de l’Observatoire de Grenoble, France Abstract. We present the Data Reduction and Handling (DRH) software developed for the SPHERE instrument. SPHERE is a second-generation instrument, designed and optimized for the direct imaging of extrasolar planets. Technical tolerances are the tightest ever for an instrument installed at the VLT, and SPHERE demands a rather unique DRH software package to accompany the data from the observation preparation to the search for planetary signals. The reduction process at the conceptual level is described and the critical issues related to above characteristics are addressed. The DRH system will be fully integrated into the ESO VLT system and it will use ESO Common Pipeline Library.

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SPHERE VLT instrument and its specific features

SPHERE (Spectro-Polarimetric High-contrast Exoplanet Research) is a project to equip the VLT with a second-generation instrument capable of delivering true images of true extrasolar planets. Under the leadership of the Labratoire d’ Astrophysique et Observatoire de Grenoble (LAOG) as P.I., and the MPIA as Co-PI, a consortium of 13 European Institutes is constructing an instrument that consists of an extreme AO system, specially adapted coronagraphs, and three focal plane instruments all specialized in high-contrast, differential imaging. These instruments are a differential imager operating in the H-band, an integral field spectrograph providing low-resolution (R∼15) spectroscopy in Jband, and the innovative “Zurich IMaging POLarimeter” ZIMPOL, providing differential poalrimetry in the visual down to polarization degrees of 10−5 . While ZIMPOL will focus on the search of reflected light from old, cold planets orbiting rather nearby stars, the other two instruments will apply differential imaging by utilizing the Methane absorption features of young giant planets. SPHERE will thus be able to find young, hot planets that still gnaw at their internal energy supply, and old, cold planets that shine purely in reflected light alike. The SPHERE instrument is designed and optimized for the sole purpose of direct imaging of extrasolar planets. A so-called “eXtreme AO system” using 1600 corrective elements updated at a rate of 1.5 kHz, and innovative coronagraphs support the three differential imagers in this task. Technical tolerances are the tightest ever for an instrument installed at the VLT, and SPHERE will be mounted directly on the Nasmyth platform to ensure maximum stability. The discovery space will only be limited by the central stars’ apparent brightness (mV < 11 mag), the apparent separation (0.′′ 1 - 6′′ ), and, of course, the 581

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ultimately achievable contrast (106 @ 0.′′ 5 or even 108 @ 1′′ in reflected and thus highly polarized light). 2.

Data Reduction and Handling System Overview

SPHERE is a highly specialized instrument which stretches the control of technical tolerances to the limits both during the design and manufacturing phases, and particularly during its many extensive calibration procedures. It is clear, that with such an instrument the greatest care must be taken to ensure that quality of the data taken at the telescope indeed matches the excellence of the instrument itself. This is why it was decided that SPHERE needs a rather unique ‘Data Reduction and Handling’ (DRH) software package which accompanies the data from the state of observation preparation – i.e. optimizing target lists, preparing and scheduling observations and calibrations, via the reduction of raw data as they come from the instrument’s detectors, to the analysis and search for planetary signals and the final inclusion of detected candidates in the target lists and the scheduling of follow-up observations. Fig. 1 gives an overview of the modules of SPHERE DRH.

Figure 1.

Overview of the SPHERE data reduction and handling software.

The proper SPHERE pipeline is divided in three instrument pipelines, namely, IRDIS, IFS and ZIMPOL pipeline. In its turn, each instrument pipeline consists of two parts: the Data Reduction (DR) to produce master calibrated data and apply them to perform a data reduction of science raw frame generating a calibrated science frame, and the so called Data Analysis (DA) part, in which the

Data Reduction and Handling for SPHERE

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Figure 2. SPHERE data product association map for the IRDIS dual band imaging mode.

requested science SPHERE product (the parameter set of the planet candidates) are created. For the data reduction instrument pipelines the following four main purposes are foreseen: • Master calibration product: DR instrument pipelines are used to produce master calibration products (e.g. bias, flat field, wavelength calibration, etc.)

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• Calibrated science frame: using DR instruments pipeline-generated master calibration products, calibrated science frames are produced for the supported instrument modes. • Science product: basing on calibrated science frames from DR pipelines the final science product is created. • Data quality control: DR instrument pipelines are used to produce the quantitative information for control of the raw data and monitor an instrument performance (off-line quality control QC1). It is a full assessment of the quality of the raw (calibration and science) data and the derived data products. A dedicated data reduction cascade corresponds to each of the observing modes. The fig. 2 summarizes the reduction steps achieved in each recipe for the IRDIS dual band imaging mode. The task of the Quick-Look (QL) will be used to reveal anomalies in the science data, performing data reduction in the ”short term” of pipeline execution after OB is completed. The SPHERE Observation Preparation Software (OPS) is a visualization tool to assist astronomers to create and track observing programs. The SPHERE OPS will be fully compatible to existing ESO preparation tool P2PP (Comeron and Silva 2005). The SPHERE DRH will be integrated in the VLT-DFS pipeline, it will make use of the ESO Common Pipeline Library1 (Banse 2003, CPL Project Team 2005). 3.

Conclusion

SPHERE technical tolerances are the tightest ever for an instrument installed at the VLT, and it demands a rather unique DRH software package. SPHERE will be the first instrument at ESO, the data pipelines of which not only deliver nice-to-look-at data for home analysis, but also pipelines that run high-fidelity signal searches and deliver all found planetary candidates for all SPHERE data sets taken by any user. Specifically during the reduction of both calibration and science data, strict error propagation control will be designed into the DRH software in order to enable sophisticated analysis and planet signal search by modelling all instrumental and atmospheric properties. This will ensure a homogenous quality of (non-)detections achieved with SPHERE and enables reprocessing of all data when improved versions of the analysis routines become available. Acknowledgements. We are certainly in debt to all colleagues of the SPHERE project for extensive discussions which provided us with wealth of information. A. Pavlov is grateful to W. G¨ assler and M. Goto for useful discussions. References Banse, K., et al. 2003, in ASP Conf. Ser. 314, ADASS XIII, ed. F. Ochsenbein, M. Allen, & D. Egret (San Francisco: ASP), 392 CPL Project Team 2005, VLT-MAN-ESO-19500-2720 Cameron, F. and Silva, VLT-MAN-ESO-19200-1644

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The CPL is presently used by ESO as its main tool for the development of data reduction pipelines for VLT instruments