Klaus Reif

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.

Hexapod control for an active secondary mirror: general concept and test results

Active control of the secondary mirror, mainly for correction of the decentering coma, is an essential tool for an active-optics telescope. The Italian Telescopio Nazionale Galileo is equipped with a secondary mirror supported by an hexapod mechanical structure, providing a positioning control with six degrees of freedom. The hexapod system has been built and tested to characterize its performance. The results show that the errors in the positioning of the secondary mirror lead to an aberration image well below the diffraction figure of the telescope.

A proper motion study of the globular cluster M 10

We present the rst proper motion study of M 10 (NGC 6254). Absolute proper motions of about 532 stars in the eld of the globular cluster M 10 were deter- mined with respect to Hipparcos and ACT reference stars. In addition to photographic plates of Bonn and Shanghai also wide eld CCD observations as second epoch plates were used. The wide eld CCD observations show an ac- curacy comparable to that of the photographic plates. A good coincidence of the solutions based on reference stars from Hipparcos and from ACT was found. Our nal proper motions allow a sucient separation of cluster and eld stars. Two population II Cepheids were conrmed to be members of M 10. The absolute proper motion of M 10 was determined and combined with its distance from the Sun and its radial velocity. The space motion and metal- licity of M 10 indicates the characteristics of a halo object with an orbit reaching to a maximalz-distance of less than 3k pc.

The Omegacam Shutter

The shutter for OmegaCam — the 16K×16K CCD mosaic camera for the 2.6-m ESO VLT Survey Telescope (VST) — is described. The OmegaCam is a high precision photometric slit type shutter with an aperture of 370 mm×292 mm. The device was designed and built at the University of Bonn. Performance measurements show that the shortest exposure time is less than 1 msec and that 100 msec exposures are homogeneous to within ± 0.3%.

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.

BUSCA: A simultaneous 4 colour camera with 4K×4K CCDs

BUSCA (Bonn University Simultaneous Camera) is a facility instrument for the 2.2 m telescope of the Calar Alto Observatory. It is equipped with a set of dichroic filters to separate four wavelength bands and with four individual CCD systems, one for each colour channel. Three 4K×4K 15-μm pixel CCD485S (Lockheed Martin Fairchild Systems) are now in operation and fill three of the four focal planes of 12×12arcmin (60×60 mm). A thinned device has been ordered for the UV-channel. The two main advantages over traditional imaging photometry are: i) precious observing time can be saved ii) atmospheric transmission fluctuations (non-photometric conditions) have almost no effect on colour index determination as colour bands are observed simultaneously. The instrument has been tested at the 1 m telescope of Bonn University’s “Hoher List” Observatory and will have its first Calar Alto run in Spring 2000.

A flux calibration device for the SuperNova Integral Field Spectrograph (SNIFS)

Observational cosmology employing optical surveys often require precise flux calibration. In this context we present SNIFS Calibration Apparatus (SCALA), a flux calibration system developed for the SuperNova Integral Field Spectrograph (SNIFS), operating at the University of Hawaii 2.2 m telescope. SCALA consists of a hexagonal array of 18 small parabolic mirrors distributed over the face of, and feeding parallel light to, the telescope entrance pupil. The mirrors are illuminated by integrating spheres and a wavelength-tunable (from UV to IR) light source, generating light beams with opening angles of 1°. These nearly parallel beams are flat and flux-calibrated at a subpercent level, enabling us to calibrate our “telescope + SNIFS system” at the required precision.

Operating a large-area MPP-CCD with antiblooming

We describe the performance of a 2k X 2k, 15 (mu) pixel, buried channel MPP-CCD (Loral FA2048) using different operating modes and the implementation of an anti-blooming clocking technique. The CCD is part of a camera system developed at Bonn University for astronomical wide field photometry and polarimetry. Besides two basic operating modes (partially and non-inverted mode) the multi pinned phase (MPP) design additionally allows a totally inverted mode providing the strongest reduction of dark current. The disadvantage is a low full well capacity of 120000 electrons/pixel which only depends on the small implanted potential offset. As an example for optimization by choosing adequate voltages we show how this original full well capacity can be raised almost by a factor of 2 without decreasing the quality of the read-out. Finally we discuss the physical understanding and technical implementation of anti-blooming and its future application in astronomical photometry. Using clocking rates up to 2 kHz we achieve a minimum anti-blooming efficiency of 400 electrons/sec/pixel/Hz and a low spurious charge generation further reduced by using ramps or intermediate steps in the anti-blooming clocking waveforms.

Bonn Shutters for the Largest Mosaic Cameras

Bonn shutters have been developed and implemented in various CCD camera systems with apertures ranging from 110 mm×110 mm (BUSCA, Calar Alto Observatory) to 370 mm×292 mm (OmegaCam, ESO/Paranal). Larger shutters with apertures of up to 480 mm×480 mm (for Pan-STARRS) are now in development. The principles of operation are basically contiguous. The key performance parameter is high timing precision which reduces exposure non-homogeneities to less than 1 msec, i.e. <0.1% at 1 sec exposure time. In this paper we report the current status of this technology, as well as new requirements and challenges.