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Astronomical Data Analysis Software and Systems VI ASP Conference Series, Vol. 125, 1997 Gareth Hunt and H. E. Payne, eds.

Calibration and Performance Control for the VLT Instrumentation
P. Ballester, K. Banse, and P. GrosbЬl European Southern Observatory, Karl-Schwarzschildstr. 2, D-85748 Garching, Germany Abstract. The Very Large Telescop e will see first light by the end of 1997 and gradually b e equipp ed with up to 14 instruments available on the four telescop e units. The framework for data calibration and analysis of the VLT instrumentation is presented, based on the concepts of a calibration plan, pip eline calibration, quality control, and archiving of calibrated data for a ground-based observatory. The role of instrument models for observation preparation and instrument p erformance control is reviewed.

1.

Introduction

The general framework for handling VLT data op erations and processing is the Data Flow System, which is comp osed of a numb er of subsystems and foundation layers. The Data Flow System (GrosbЬl & Peron 1997) includes all services involved, from observation preparation to data analysis. In this pap er we present the pip eline and quality control parts of the system. 2. Pip eline Processing

For pip eline processing, the header structure of the data is interpreted by a Data Organizer to associate the individual Frames, identify Reduction Recip es, and create Reduction Blocks. There will b e four kinds of pip eline procedures: · Calibration Pip eline will process the data acquired during technical programs and prepare pre-calibrated solutions. Solutions may also b e derived from calibration data generated during the observing run. Derived data may individually b e submitted to the calibration archive. · Reduction Pip eline p erforms a quasi real-time calibration of scientific data obtained by supp orted templates. When p ossible, the Reduction pip eline applies pre-defined calibrated solutions to guarantee stable p erformance. When calibration data are taken during an observing program, the quality control pip eline will verify the adequacy of the derived data for this configuration. · Quality Control Pip eline provides quality assessment for instrument p erformance data and observing conditions, and tests the results of the Reduction Pip eline. 415

© Copyright 1997 Astronomical Society of the Pacific. All rights reserved.


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Ballester, Banse, and GrosbЬl
Tech. Prg. B Tech. Prg. C

Tech. Prg. A

Calibration Pipeline Garching (DFS)

Derived Data QC/DFIS Verification Calibration Database

Replication

Derived Data

On-Line Calibration Database

Derived Data

Rescheduling (DFIS)

Observation Program (Technical, Scientific) Science Data Science Data Calibration Data

Replication Archive

Reduction Pipeline Paranal (DFO)

Quality Control Pipeline Paranal (DFO)

Observatory Pipeline Reduced Science Data QC Results Garching (DFIS)

QC Status Preparation

Reduced Frame + QC Status

· Observatory Pip eline allows re-reduction procedures based on b etter derived data and algorithms (re-calibration, on-the-fly calibration, final archive preparation, etc.).

3.

Quality Control

Quality Control verifies the conditions and the results with which the Reduction Pip eline p erforms its task. To this end, the Quality Control subsystem verifies the instrumental and observational conditions and compares them to the sp ecifications of the Reduction Pip eline. In addition, Quality Control p erforms some verification of the data processed by the Pip eline. Instrument p erformance, ob-


Calibration and Performance Control for the VLT

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serving conditions, and pip eline results contribute to the estimation of a Quality Status attached to each Reduced Frame. The following levels of testing will b e p erformed in the context of Quality Control. These tasks are presented in a sequence corresp onding to the exp ected level of automation: (i) completion testing, (ii) routine testing: detector, calibration lamps, arc lines, (iii) instrument function testing: focus, instrument resp onse, and (iv ) sp ecific testing: scattered light, non-linearities. Some of these tasks will b e implemented in the Quality Control pip eline and b e executed during observations. Others will b e implemented as interactive procedures. An imp ortant asp ect of Quality Control will b e the production and maintenance of instrument models for the purp ose of exp osure time calculation and instrument control. 4. Instrument Mo del Framework

The development of an instrument model framework consists of a close collab oration b etween the ESO Data Management Division (DMD) and Space Telescop e Europ ean Coordinating Facility (ST/ECF). The VLT and the HST facilities have quite similar demands, b ecause b oth astronomical observatories are committed to rapid dissemination of data from a variety of instruments to the world-wide community at a large. One of the VLT instruments under construction is the high resolution echelle sp ectrograph UVES; first light is planned for 1999. The DMD model for this instrument now succeeds in predicting the geometrical asp ects of observational data to b etter than one resolution element (pixel) of the detector. In parallel, the ST/ECF has produced a computer model for the low-resolution Faint Object Sp ectrograph (FOS) on HST (Rosa 1995). This software is optimized for simulating internally scattered light, which is a serious nuisance for observations of faint targets. A direct result of such models is exp osure time calculators, which observers can use to estimate the length of each exp osure when preparing an observing program. To allow wide access by the scientific community to such tools, the software for these calculators is b eing made available on the Internet. The success of these first modeling exp eriments has led to the definition of a common framework for the development of such models, and to the creation of a versatile software package and associated database. Within this environment, a slight modification of the UVES software was efficiently re-used to model an existing high-resolution sp ectrograph--CASPEC at the ESO 3.6metre telescop e--and is currently b eing transformed into a model for the STIS sp ectrograph on HST. The next steps will b e to provide models for all those instruments that will b ecome op erational on the VLT and the HST in the coming years, and to study further the impact of the improved calibrations on new data analysis techniques. References GrosbЬl, P., & Peron, M. 1997, this volume, 22 Rosa, M. R. 1995, in Calibrating and Understanding HST and VLT instruments, ed. P. Benvenuti, ESO/ST-ECF Workshop, ESO, 43