Ralf Klein

CIAO: wavefront sensors for GRAVITY

GRAVITY is a second generation near-infrared VLTI instrument that will combine the light of the four unit or four auxiliary telescopes of the ESO Paranal observatory in Chile. The major science goals are the observation of objects in close orbit around, or spiraling into the black hole in the Galactic center with unrivaled sensitivity and angular resolution as well as studies of young stellar objects and evolved stars. In order to cancel out the effect of atmospheric turbulence and to be able to see beyond dusty layers, it needs infrared wave-front sensors when operating with the unit telescopes. Therefore GRAVITY consists of the Beam Combiner Instrument (BCI) located in the VLTI laboratory and a wave-front sensor in each unit telescope Coudé room, thus aptly named Coudé Infrared Adaptive Optics (CIAO). This paper describes the CIAO design, assembly, integration and verification at the Paranal observatory.

LAIWO: a new wide-field CCD camera for Wise Observatory

LAIWO is a new CCD wide-field camera for the 40-inch Ritchey-Chretien telescope at Wise Observatory in Mitzpe Ramon/Israel. The telescope is identical to the 40-in. telescope at Las Campanas Observatory, Chile, which is described in [2]. LAIWO was designed and built at Max-Planck-Institute for Astronomy in Heidelberg, Germany. The scientific aim of the instrument is to detect Jupiter-sized extra-solar planets around I=14-15 magnitude stars with the transit method, which relies on the temporary drop in brightness of the parent star harboring the planet. LAIWO can observe a 1.4 x 1.4 degree field-of-view and has four CCDs with 4096*4096 pixels each The Fairchild Imaging CCDs have a pixel size of 15 microns. Since they are not 2-side buttable, they are arranged with spacings between the chips that is equal to the size of a single CCD minus a small overlap. The CCDs are cooled by liquid nitrogen to a temperature of about -100 °C. The four science CCDs and the guider CCD are mounted on a common cryogenic plate which can be adjusted in three degrees of freedom. Each of these detectors can also be adjusted independently by a similar mechanism. The instrument contains large shutter and filter mechanisms, both designed in a modular way for fast exchange and easy maintenance.

Design and tests of the MIDI detector subsystem

In this paper we present the results of the first tests performed at MPIA on the detector system of MIDI, the Mid-IR interferometric instrument for VLTI. Interferometric observations at 10 micrometers , while having advantages with respect to near-IR and optical wavelengths in terms of seeing and coherence time, must face the problem of the strong thermal background coming from the telescope and from the sky. In order to reach background limited performances in the observing conditions foreseen for MIDI at Paranal, the detector and the associated read-out electronics must comply to strict requirements. The different MIDI observing modes are characterized by widely different values of background per pixel; in high background conditions the main problem is to avoid saturation, while in medium-background conditions we are close to read-out noise limited conditions. Therefore, large integration capacity and high speed must be reached with low read-out noise. The read-out electronic chain is described; at maximum speed, one full 16-bit 320 X 240 pixels2 frame can be read in 3.6 msec. Since only a portion of the detectors field of view will contain useful information, only selected parts of the detector will be read, thus increasing the frame rate. We briefly review the different read-out strategies adopted; the correspondent operations on the detector are described. We also present the results of the first tests performed at MPIA on the whole detector subsystem, using a bare multiplexer of the selected detector (a 320 X 240 Si:As IBC array from Raytheon Corp.).

A versatile motion control system for astronomical instrumentation

With steadily increasing telescope sizes and the growing complexity of scientific instruments, there is an ever-growing demand for improved electronics, controlling all the different optical parts on moving mechanisms. Among competing requirements are, on one hand, the increasing number of actuators, with high-precision positioning in closed and open loop, and on the other hand, smaller sizes, low power and restricted heat emission. A specific challenge is accommodating mechanisms that operate in infrared instrumentation at cryogenic temperatures down to 60 Kelvin. In this area piezo motors offer promising solutions. To fulfill these different demands a competitive motion control system has been developed at the Max-Planck-Institut für Astronomie (MPIA) in Heidelberg, Germany. A modular chassis with standardized boards provides best solutions for extensive tasks. High and low power DC servo motors, brushless DC servo motors, stepper motors and piezo motors with different technologies are supported. Diversity position feedback capabilities, like incremental and absolute encoders for non cryogenic and capacitive sensors and resolvers for cryogenic applications, are provided.

New read-out electronics concept for visual and infrared detector arrays in astronomical instrumentation

With the building of scientific camera systems for astronomical purposes in mind, the Max-Planck-Institut fuer Astronomie (MPIA) has recently started developing new visual and infrared detector Read-out systems. Due to the modular design, the electronics components can be configured for a wide range of currently available IR-detectors and CCDs. The new Read-out Electronics are able to handle single or multiple detector systems with up to 144 input channels, feature high-speed data transfer and low power dissipation and additionally the system size is small and lightweight. The design is divided in four functional groups: controller board with variable Pattern Generator and fast fiber link, clock/bias board, analog to digital converter board and the PCI data receiver board which writes the incoming data into the computer memory. This design is highly versatile and allows for a wide variety of applications. The high data transfer rate, small size and low heat dissipation makes these Read-out Electronics ideal for relatively large focal plane arrays. The first instrument running with the new Read-out Electronics will be PANIC (Panoramic Near Infrared Camera) at the 2.20 m telescope on Calar Alto.

Experiences with Raytheon Si: As IBC detector arrays for mid-IR interferometric observations

Interferometric observations at 10 micron combine the difficulties of the relatively new interferometric techniques with the problems of overcoming the strong and highly variable thermal background which are typical of thermal infrared observations. In particular, the detector subsystem must comply to strict requirements in terms of stability, of read noise, and of read out speed. Here we present the results obtained during laboratory test of MIDI, the Mid-IR interferometric instrument for VLTI. We selected as detector for the MIDI instrument a Raytheon 320x240 IBC array. We will discuss some of the aspects of the foreseen operation of MIDI, and the methods adopted to implement those on our detector system. We will show our results on detector stability, on its performances (in particular Quantum efficiency and read-out noise), and on the reaction to high fluxes. By using the possibility of hardware windowing, frame times of the order of 2 ms can be reached. Finally, we will show the characteristics of the detector when used in interferometric mode during tests of the whole MIDI instrument with both monochromatic and broad band calibration sources.