Armin Silber

CRIRES: A High Resolution Infrared Spectrograph for ESO’s VLT

CRIRES is a cryogenic, pre-dispersed, infrared echelle spectrograph designed to provide a resolving power lambda/(Delta lambda) of 105 between 1 and 5mu m at the Nasmyth focus B of the 8m VLT unit telescope #1 (Antu). A curvature sensing adaptive optics system feed is used to minimize slit losses and to provide diffraction limited spatial resolution along the slit. A mosaic of 4 Aladdin~III InSb-arrays packaged on custom-fabricated ceramics boards has been developed. This provides for an effective 4096x512 pixel focal plane array, to maximize the free spectral range covered in each exposure. Insertion of gas cells to measure high precision radial velocities is foreseen. For measurement of circular polarization a Fresnel rhomb in combination with a Wollaston prism for magnetic Doppler imaging is foreseen. The implementation of full spectropolarimetry is under study. This is one result of a scientific workshop held at ESO in late 2003 to refine the science-case of CRIRES. Installation at the VLT is scheduled during the first half of 2005. Here we briefly recall the major design features of CRIRES and describe its current development status including a report of laboratory testing.

HAWK-I: A new wide-field 1- to 2.5-μm imager for the VLT

HAWK-I (High Acuity, Wide field K-band Imaging) is a 0.9 μm - 2.5 μm wide field near infrared imager designed to sample the best images delivered over a large field of 7.5 arcmin x 7.5 arcmin. HAWK-I is a cryogenic instrument to be installed on one of the Very Large Telescope Nasmyth foci. It employs a catadioptric design and the focal plane is equipped with a mosaic of four HAWAII 2 RG arrays. Two filter wheels allow to insert broad band and narrow band filters. The instrument is designed to remain compatible with an adaptive secondary system under study for the VLT.

MACAO-VLTI adaptive optics systems performance

In April and August ’03 two MACAO-VLTI curvature AO systems were installed on the VLT telescopes unit 2 and 3 in Paranal (Chile). These are 60 element systems using a 150mm bimorph deformable mirror and 60 APD’s as WFS detectors. Valuable integration & commissioning experience has been gained during these 2 missions. Several tests have been performed in order to evaluate system performance on the sky. The systems have proven to be extremely robust, performing in a stable fashion in extreme seeing condition (seeing up to 3”). Strehl ratio of 0.65 and residual tilt smaller than 10 mas have been obtained on the sky in 0.8” seeing condition. Weak guide source performance is also excellent with a strehl of 0.26 on a V~16 magnitude star. Several functionalities have been successfully tested including: chopping, off-axis guiding, atmospheric refraction compensation etc. The AO system can be used in a totally automatic fashion with a small overhead: the AO loop can be closed on the target less than 60 sec after star acquisition by the telescope. It includes reading the seeing value given by the site monitor, evaluate the guide star magnitude (cycling through neutral density filters) setting the close-loop AO parameters (system gain and vibrating membrane mirror stroke) including calculation of the command-matrix. The last 2 systems will be installed in August ’04 and in the course of 2005.

MACAO-VLTI: an adaptive optics system for the ESO interferometer

MACAO stands for Multi Application Curvature Adaptive Optics. A similar concept is applied to fulfill the need for wavefront correction for several VLT instruments. MACAO-VLTI is one of these built in 4 copies in order to equip the Coude focii of the ESO VLTs. The optical beams will then be corrected before interferometric recombination in the VLTI (Very Large Telescope Interferometer) laboratory. MACAO-VLTI uses a 60 elements bimorph mirror and curvature wavefront sensor. A custom made board processes the signals provided by the wavefront detectors, 60 Avalanche Photo-diodes, and transfer them to a commercial Power PC CPU board for Real Time Calculation. Mirrors Commands are sent to a High Voltage amplifier unit through an optical fiber link. The tip-tilt correction is done by a dedicated Tip-tilt mount holding the deformable mirror. The whole wavefront is located at the Coude focus. Software is developed in house and is ESO compatible. Expected performance is a Strehl ratio sligthly under 60% at 2.2 micron for bright reference sources (star V<10) and a limiting magnitude of 17.5 (Strehl ~0.1). The four systems will be installed in Paranal successively, the first one being planned for June 2003 and the last one for June 2004.

HAWK-I: the new wide-field IR imager for the VLT

HAWK-I is a new wide-field infrared camera under development at ESO. With four Hawaii-2RG detectors, a 7.5 arcminute square field of view and 0.1 arcsecond pixels, it will be an optimum imager for the VLT, and a major enhancement to existing and future infrared capabilities at ESO. HAWK-I will eventually make use of ground-layer AO achieved through a deformable secondary mirror/laser guide star facility planned for the VLT.

Photon counting arrays for astrophysics

A compact system for counting and time-tagging single photons is presented, based on a monolithic array sensor of 60 pixels able to detect single photons, namely the single-photon avalanche diode array (SPADA). First, the working principle and performance of the single-photon detector pixel is detailed, with particular attention paid to monolithic array integration. Then the electronics needed to quench each pixel after avalanche ignition, namely the active-quenching circuit (AQC) is discussed, since the features of this quenching electronics dramatically affect the operating conditions of the detector, hence its actual performance. The discussion then focuses on integration of the SPADA system into Astrophysics applications such as adaptive optics, fast-transient imaging and atmospheric layer sensing. The whole electronics necessary to control SPADA operating conditions and temperature is also described, together with the complete opto-mechanics used to focus the telescope pupil onto the detector. Finally, experimental results are reported.

First light of the ESO laser guide star facility

Two teams of scientists and engineers at Max Planck Institut fuer Extraterrestrische Physik and at the European Southern Observatory have joined forces to design, build and install the Laser Guide Star Facility for the VLT. The Laser Guide Star Facility has now been completed and installed on the VLT Yepun telescope at Cerro Paranal. In this paper we report on the first light and first results from the Commissioning of the LGSF.

The OmegaCAM 16K x 16K CCD detector system for the ESO VLT Survey Telescope (VST)

A 16K x 16K, 1 degree x 1 degree field, detector system was developed by ESO for the OmegaCAM instrument for use on the purpose built ESO VLT Survey Telescope (VST). The focal plane consists of an 8 x 4 mosaic of 2K x 4K 15um pixel e2v CCDs and four 2K x 4K CCDs on the periphery for the opto-mechanical control of the telescope. The VST is a single instrument telescope. This placed stringent reliability requirements on the OmegaCAM detector system such as 10 years lifetime and maximum downtime of 1.5 %. Mounting at Cassegrain focus required a highly autonomous self-contained cooling system that could deliver 65 W of cooling power. Interface space for the detector head was severely limited by the way the instrument encloses the CCD cryostat. The detector system features several novel ideas tailored to meet these requirements and described in this paper: Key design drivers of the detector head were the easily separable but precisely aligned connections to the optical field flattener on the top and the cooling system at the bottom. Material selection, surface treatment, specialized coatings and in-situ plasma cleaning were crucial to prevent contamination of the detectors. Inside the cryostat, cryogenic and electrical connections were disentangled to keep the configuration modular, integration friendly and the detectors in a safe condition during all mounting steps. A compact unit for logging up to 125 Pt100 temperature sensors and associated thermal control loops was developed (ESOs new housekeeping unit PULPO 2), together with several new modular Pt100 packaging and mounting concepts. The electrical grouping of CCDs based on process parameters and test results is explained. Three ESO standardized FIERA CCD controllers in different configurations are used. Their synchronization mechanism for read-out is discussed in connection with the CCD grouping scheme, the shutter, and the integrated guiding and image analysis facility with four independent 2K x 4K CCDs. An illustration of the data chain performance from CCD output to storage on hard-disk gives an impression of the challenge to shift 512 MB of data within 45 seconds via the standardized hierarchical ESO data acquisition network. Finally the safety and emergency features of the overall system are presented.

The CRIRES InSb megapixel focal plane array detector mosaic

For the high-resolution IR Echelle Spectrometer CRIRES (1-5 μm range), to be installed at the VLT in 2005, ESO is developing a 512 x 4096 pixels focal plane array mosaic based on Raytheon Aladdin III InSb detectors with a cutoff wavelength of 5.2 microns. To fill the useful field of 135 mm in the dispersion direction and 21 mm in the spatial direction and to maximize simultaneous spectral coverage, a mosaic solution similar to CCD mosaics has been chosen. It allows a minimum spacing between the detectors of 264 pixels. ESO developed a 3-side buttable mosaic package for both the Aladdin II and Aladdin III detectors which are mounted on multilayer co-fired AlN ceramic chip carriers. This paper presents the design of the CRIRES 512 x 4096 pixel Aladdin InSb focal plane array and a new test facility for testing mosaic focal planes under low flux conditions.

New challenges for the maintenance strategies on large astronomical facilities at remote observing sites

The Change from a reacting to a proactive maintenance concept represents for large Observatories at remote operational sites a new challenge, considering the increasing numbers of complex subsystems. Conventional operational maintenance models will not cover all the requirements, will lead to more down time and the operational cost cannot be reduced. For the successful astronomical observation with large telescope facilities new strategies have to be applied. In this contribution we will demonstrate on the example of the 78 Cryogenic Sub-systems of ALMA how a proactive maintenance strategy help to increase the efficiency, to reduce the operational cost and the required staff resources. With respect to the growing number of complex subsystems on future telescope facilities the operational staff needs proper diagnostic and monitoring tools to allow a precise prediction respectively synchronization of the service activities. This leads away from a pure scheduling of preventive maintenance and enables a longer availability of the subsystems as tendencies and performance are monitored and controlled. Having this strategy considered during the developing phase of future large astronomical facilities allows the optimization of the required Infrastructure, a proper definition of the LRU1 strategy and to which level maintenance can be cost efficient on site.