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Part III: DEIMOS Calibration: Procedures and Database Requirements - DRAFT


The term ``calibrations'' encompasses a large range of issues and procedures, and the current document is not exhaustive. We focus on photometric and astrometric calibration of direct images through the standard DEIMOS filter set (BVRI) and flux and wavelength calibration of multislit spectra, including longslit spectra of single objects as a special case. These categories comprise the great bulk of DEIMOS data. We further assume that the instrument consists of Side A only, although the coordinate systems for Side B have also been defined.

Two data calibration modes are considered:

tex2html_wrap_inline5860 Pipeline Mode:
This is analogous to the current mode for reducing Hubble Space Telesccope data, in which a standard suite of reduction programs removes the instrumental signature using a stored library of calibration data. The necessary software would be supplied by the DEIMOS project and would run both at Keck and at the observer's home institution (provided the appropriate hardware and operating systems are available). The ultimate aim is that pipeline data reduction will occur on-line as the data are taken, with observers returning home with data from which the instrumental signature has been removed. A further longterm aim is to minimize taking calibration data during observing and to use instead the stored library of calibration data to the fullest extent.

Pipeline Mode at this point is only a goal. Its implementation is not supported by the current DEIMOS software budget, and it further presupposes stability of the (Keck II Telescope + DEIMOS) hardware system, which is currently unproven. Nevertheless, we are hopeful of implementing Pipeline Mode eventually and are designing the DEIMOS database to be able to accomodate it.

tex2html_wrap_inline5860 Baseline Mode:
Baseline mode is the traditional mode of data reduction at ground-based observatories, in which each observer is responsible for gathering the necessary calibration data and reducing the data. We recommend recipes for doing this with DEIMOS and outline a partial long-term calibration data base that will be useful for certain aspects of Baseline Mode calibrations ??. Software and database entires needed to implement Baseline Mode should be available at instrument commissioning or soon thereafter.

We begin with a discussion of coordinate systems, which are needed to understand the relationships between sky, focal plane and detector. This is followed by a description of the major calibration elements, the major dependencies for each of these elements, and general procedures for addressing each. We next discuss the detector calibrations, imaging data and spectroscopic data in turn, from the perspective of specific procedures and database products necessary for calibrating each stream of data. The final section covers routine diagnostic tests to monitor system stability, e.g., optical alignments.

This document presumes a working knowledge of the DEIMOS instrument, to be found in the Preliminary and Critical Design Reports, the Software Preliminary and Critical Design Reports, the Flexure Compensation System Report (TBD), and ??.

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