4 Overview of Data Procedures & Database Products

 

The following four chapters provide detailed information about calibrations required to characterize DEIMOS at commissioning, procedures needed to calibrate DEIMOS science data, products that will be maintained in the DEIMOS database, and instructions for creating those products. These chapters cover:

Engineering Calibrations:

Those calibrations needed at commissioning, which must be performed prior to science observations: slitmask astrometry, TV astrometry, determining relative alignment of CCDs.

Detector Calibrations:

Those steps needed to characterize and remove the signature of the detector and electronics, independent of the light falling on the detector: bias level, bias structure, dark counts, CR-cleaning.

Imaging Calibrations:

Those steps needed to characterize and remove the signature of the total system in direct imaging mode: flat-fielding, flux calibration, geometric distortions.

Spectral Calibrations:

Those steps needed to characterize and remove the signature of the total system in spectroscopic mode: flat-fielding, geometric distortions, wavelength calibration, flux calibration.

Engineering calibrations are of little direct interest to the user, but are of considerable importance to the acquisition of high-quality data. The remaining three types of calibrations are referred to as science calibrations, and must be carried out by the user or a data-reduction pipeline. A flowchart of these operations is shown in Figure ??, and a summary of the scince calibration steps/elements is given in the Table. [Figure to be finished...]

Each of the following chapters is organized to provide a description of terms, background information and relevant concerns regarding certain processes, and a brief description of each calibration step. This is followed by a summary of necessary database entries and instructions for how each will be created (the instructions will eventually be turned into coded instrument-control scripts which can be run with little input from the instrument specialist responsible for maintaining the calibration database). Finally, outstanding issues are listed at the end of each chapter.

All calibration procedures and products are required for pipeline mode. We identify two levels of pipeline mode, Phase 1 and Phase 2, as well as a pre-pipeline, Baseline mode. Baseline mode will be delivered at commissioning. We hope to deliver Phase 1 pipeline within one year of commissioning. Phase 2 is somewhat dependent upon the performance of the Phase 1 pipeline and the instrument, and its implementation is uncertain. Since Baseline mode requirements are a subset of Phase 1 pipeline mode requirements, we describe the calibration procedures and database products from the perspective of pipeline mode; variations for baseline mode will be noted as needed. The instructions for creating database entities can be used by observers to obtain necessary calibration images in baseline mode.

4.1 Calibration Slitmasks

The calibration of certain properties require special slitmasks. These are described below, and their use is detailed in the following chapters.

Grid-of-holes (GOH) mask:

a rectangular grid of very small holes at spacings of 1 cm (??) along grid patterns at 5 cm (??) for a total of (??) holes [TBD].

Line-of-holes (LOH) mask:

a line of rectangular apertures cut on a regular grid at 10 arcsec spacing. The apertures should be wide (3 arcsec in y) and fairly short (1.5 arcsec in x) so that small variations in slit area will not have a significant effect on the flux (;SPMlt;;SPMlt; 1%). (The x-length will be adjusted to account for the mask curvature and thickness of the mask stock, so the effective aperture remains constant across the mask.)

Line-of-slitlets (LOS) masks:

Set of masks, with line of slitlets at y-spacings 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 7.0 and 8.0 arcmin from the telescope axis (8 in total). Each LOS consists of a line of 100 rectangular slitlets each arcsec, separated by 3 arcsec, across the x-range of 8.5 arcmin.

In addition, there will be a number of slitmasks of astrometric fields used in slitmask astrometry.