Introduction

  This chapter describes the design and the philosophy of the CCD package, its main features, and how to use the tools most efficiently.

With the installation of new instruments on the La Silla Telescopes in addition to the availability of CCDs offering large pixel areas and higher quantum efficiency, the variety of observing modes has grown and, as an obvious consequence, the amount and the diversity of data taken have dramatically increased. It is clear that the MIDAS CCD reduction software should be able to cope with these improvements and hence requires compatibility with the hardware as it is offered to the community.

When designing the basic layout of the CCD software the following basic requirements were kept in mind:

• it should be robust;
• it should be user friendly, easy to use;
• it should offer processing possibilities for a large variety of instruments;
• it should be able to operate both in an automatic mode (to handle large quantities of data) as well as in single command mode (for single image analysis);
• it should offer flexible reduction procedures;
• it should be intelligent.

How intelligent the system is depends on the capabilities of other parts in the data acquisition, archiving, and reduction systems. In this respect the development of the CCD package took place at the right time: the MIDAS Data Organizer package offers the possibility to quickly create a MIDAS table containing the science frames to be reduced and their associated calibration frames. The CCD package uses this facility that is based on selection criteria, similar to the ones that are used for the MIDAS table file system. Also, the ESO Archive project has accomplished that a number of telescope and instrument specifications, needed to come to a (partially) automated CCD reduction, can be retrieved from the frame descriptors.

In order not to re-invent the wheel, existing CCD packages have been consulted, and, when useful, ideas have been implemented in the MIDAS CCD software. Its design has largely profited from the IRAF CCDRED package written by Frank Valdes. Parts of its documentation are used for this manual. Also, discussions with Peter Draper, the author of the STARLINK CCDPACK package, are acknowledged.

The document is split into several sections. They describe in detail the various steps in the CCD reduction, starting from reading in the science and calibration frames and ending with the final cosmetic fix up of the final calibrated frames. Some background information about CCD detectors can be found in the MIDAS Users' Guide, Volume B, Appendix B. Additional information about the CCD commands can be obtained from their help descriptions.

The emphasis of the CCD package is on direct imaging. However, since the first processing steps for spectral data are rather similar to direct imaging major parts of its functionality can also be used for processing these data.

*** WARNING ***

The MIDAS CCDRED context is partly based on the current status of the ESO Archiving project as well as the Data Organizer Context, in particular with regard to exposure types and naming of files. Since both projects may be subject to changes in the future, and because of user experiences and suggestions for improvements, the CCDRED context may undergo adjustments accordingly.