Reiner Harke

OmegaCAM: wide-field imaging with fine spatial resolution

OmegaCAM is the wide-field camera for the VLT Survey Telescope being completed for ESOs Paranal observatory. The instrument, as well as the telescope, have been designed for very good, natural seeing-limited image quality over a 1 degree field. At the heart of the project are a square-foot photometric shutter, a 12-filter storage/exchange mechanism, a 16k x 16k CCD detector mosaic, and plenty of software for instrument control and data handling, analysis and archiving.

OmegaCAM: the 16k×16k CCD camera for the VLT survey telescope

OmegaCAM, a 16k×16k-pixel wide field optical camera, and the VLT Survey Telescope (VST) that is to host it, will constitute a major sky surveying machine that becomes operational in 2004 at ESO’s Paranal Observatory. It maps one square degree of sky with 0.21 arcsec sized pixels. Both individual programs, including monitoring programs, and large sky survey programs are planned. Here we present the integrated design of the VST-OmegaCAM survey machine, including the hardware (large filters and shutter, cf(4836-34)), the VLT compliant control software (cf(4848-10)) and the strongly procedurized observing and calibration strategies. The strict data taking procedures facilitate pipeline data reduction procedures both for the calibration and the science data. In turn, the strongly procedurized data handling allows European-wide federations of data-products. The ASTRO-WISE consortium aims to provide a survey system that makes this possible. On-the-fly re-processing of archival data on the request of individual users with their own plug-ins or newly derived calibrations sets are facilitated in an internationally distributed system. Compared to the classical more static wide-field image archives the newly designed system is characterized by a much more dynamical type of archiving.

Masking techniques at the focal plane of the FORS instruments

The FORS instruments are focal reducers and spectrographs which are built in two copies for the unit telescopes UT1 and UT2 of the ESO/VLT by a consortium of University Observatories. An overview of the instrument capabilities is given in a separate paper at this conference.

OmegaCAM - Technical Design and Performance

The 256-Mega-Pixel imager OmegaCAM will become the wide-field camera at the VLT-Survey-Telescope of the ESO Paranal Observatory. The camera will cover 1 square-degree field of view at the 2.6-metre VST telescope with 16k×16k pixel resolution. The opto- and electro-mechanical design is the responsibility of a Dutch-German-Italian consortium whereas the cryogenic detector system is built by ESO. The design phase had been finalized with a successful Final-Design-Review in autumn 2001. Procurement and manufacturing is ongoing till the end of the year 2002 followed by an extensive testing period before Preliminary-Acceptance-in-Europe. The paper will present the camera design including the results of design analyses and performance assessments of which optical and finite-element-analyses will be emphasized. The actual design of large-format optical filters will be addressed as well. Their procurement turned out as a challenging issue.

Image motion and flexure compensation of the FORS spectrographs

One of the most critical issues in designing a spectrograph is the motion of opto-mechanical components due to flexure especially when it will be mounted to the Cassegrain focus of a telescope. Image motion on the detector has to be kept small in order not to affect the value of the scientific data. The FORS spectrographs fulfil those requirements by a proper design and by a passive compensation of the instrumental flexure. Image motion of the 2 metric tons instrument could be reduced in this way to a tiny fraction of one pixels size thus not affecting the data gathered with those spectrographs. It is tested and approved at a telescope simulator that all specifications regarding those motions are fully met. A fine tuning flexure compensation is built into the spectrographs design and is tested on its tuning range which allows to adapt the compensation to effects eventually caused by the Cassegrain flange of the telescope.