A. Böhm

CARMENES: Calar Alto high-resolution search for M dwarfs with exo-earths with a near-infrared Echelle spectrograph

CARMENES (Calar Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and optical Echelle Spectrographs) is a next-generation instrument to be built for the 3.5m telescope at the Calar Alto Observatory by a consortium of Spanish and German institutions. Conducting a five-year exoplanet survey targeting ~ 300 M stars with the completed instrument is an integral part of the project. The CARMENES instrument consists of two separate spectrographs covering the wavelength range from 0.52 to 1.7 μm at a spectral resolution of R = 85, 000, fed by fibers from the Cassegrain focus of the telescope. The spectrographs are housed in a temperature-stabilized environment in vacuum tanks, to enable a 1m/s radial velocity precision employing a simultaneous ThAr calibration.

CONICA design, performance and final laboratory tests

CONICA has been developed by a German consortium under an ESO contract, to serve together with the VLT adaptive optics system NAOS as a high resolution multimode NIR camera and spectrograph. We report on final laboratory performance tests carried out during the integration period with the adaptive optics. Apart from an outline of the capabilities of this multimode instrument such as high resolution imaging, spectroscopy, Fabry-Perot and a sophisticated internal flexure compensation, we will turn our attention to a detailed examination of the detector characteristics to fully exploit the potential of the ALADDIN array.

Optimizing the transmission of the GRAVITY/VLTI near-infrared wavefront sensor

The GRAVITY instrument’s adaptive optics system consists of a novel cryogenic near-infrared wavefront sensor to be installed at each of the four unit telescopes of the VLT. Feeding the GRAVITY wavefront sensor with light in the 1.4 - 2.4 micrometer band, while suppressing laser light originating from the GRAVITY metrology system, custom-built optical components are required. Here we report on optical and near-infrared testing of the silicon entrance windows of the wavefront sensor cryostat and other reflective optics used in the warm feeding optics.

LINC-NIRVANA for the large binocular telescope: setting up the world’s largest near infrared binoculars for astronomy

LINC-NIRVANA (LN) is the near-infrared, Fizeau-type imaging interferometer for the large binocular telescope (LBT) on Mt. Graham, Arizona (elevation of 3267 m). The instrument is currently being built by a consortium of German and Italian institutes under the leadership of the Max Planck Institute for Astronomy in Heidelberg, Germany. It will combine the radiation from both 8.4 m primary mirrors of LBT in such a way that the sensitivity of a 11.9 m telescope and the spatial resolution of a 22.8 m telescope will be obtained within a 10.5×10.5 arcsec 2 scientific field of view. Interferometric fringes of the combined beams are tracked in an oval field with diameters of 1 and 1.5 arcmin. In addition, both incoming beams are individually corrected by LN’s multiconjugate adaptive optics system to reduce atmospheric image distortion over a circular field of up to 6 arcmin in diameter. A comprehensive technical overview of the instrument is presented, comprising the detailed design of LN’s four major systems for interferometric imaging and fringe tracking, both in the near infrared range of 1 to 2.4 μm, as well as atmospheric turbulence correction at two altitudes, both in the visible range of 0.6 to 0.9 μm. The resulting performance capabilities and a short outlook of some of the major science goals will be presented. In addition, the roadmap for the related assembly, integration, and verification process are discussed. To avoid late interface-related risks, strategies for early hardware as well as software interactions with the telescope have been elaborated. The goal is to ship LN to the LBT in 2014.

High-precision cryogenic wheel mechanisms of the JWST/MIRI instrument: Performance of the flight models

The Mid Infrared Instrument (MIRI) aboard JWST is equipped with one filter wheel and two dichroic-grating wheel mechanisms to reconfigure the instrument between observing modes such as broad/narrow-band imaging, coronagraphy and low/medium resolution spectroscopy. Key requirements for the three mechanisms with up to 18 optical elements on the wheel include: (1) reliable operation at T = 7 K, (2) high positional accuracy of 4 arcsec, (3) low power dissipation, (4) high vibration capability, (5) functionality at 7 K < T < 300 K and (6) long lifetime (5-10 years). To meet these requirements a space-proven wheel concept consisting of a central MoS2-lubricated integrated ball bearing, a central torque motor for actuation, a ratchet system with monolithic CuBe flexural pivots for precise and powerless positioning and a magnetoresistive position sensor has been implemented. We report here the final performance and lessons-learnt from the successful acceptance test program of the MIRI wheel mechanism flight models. The mechanisms have been meanwhile integrated into the flight model of the MIRI instrument, ready for launch in 2014 by an Ariane 5 rocket.

Cryogenic wheel mechanisms for the Mid-Infrared Instrument (MIRI) of the James Webb Space Telescope (JWST): detailed design and test results from the qualification program

The Mid-Infrared Instrument (MIRI) of the James Webb Space Telescope, scheduled for launch in 2013, will provide a variety of observing modes such as broad/narrow-band imaging, coronagraphy and low/medium resolution spectroscopy. One filter wheel and two dichroic-grating wheel mechanisms allow to configure the instrument between the different observing modes and wavelength ranges. The main requirements for the three mechanisms with up to 18 positions on the wheel include: (1) reliable operation at T ~ 7 K, (2) optical precision, (3) low power dissipation, (4) high vibration capability, (5) functionality at 6 K < T < 300 K and (6) long lifetime (5-10 years). To meet these stringent requirement, a space-proven mechanism design based on the European ISO mission and consisting of a central bearing carrying the optical wheels, a central torque motor for wheel actuation, a ratchet system for precise and powerless positioning and a magnetoresistive position sensor has been selected. We present here the detailed design of the flight models and report results from the extensive component qualification.

The cold focal plane chopper of HERSCHEL's PACS instrument

HERSCHELs 3.5 m primary mirror will be passively cooled to T ~ 80 K in the L2 orbit. In order to reduce the effects of the remaining high thermal background on the sensitive far infrared detectors (60..210 μm), a focal plane chopper is a vital element in the entrance optics of the imaging and spectroscopic instrument PACS. A gold coated 32 × 26 mm2 plane mirror, suspended by two flexural pivots and driven by a linear motor, allows for precise square wave chopping with up to 9° throw at a frequency 10 Hz with a position accuracy of 1 arcmin. The power required at T ~ 4 K is about 1 mW. The chopper has undergone an extensive qualification programme, including 650 million cold chop throws, 15 cold-warm-cold thermal cycles, 3-axis 26 G-vibration at T ~ 4 K etc. Five models were built and thoroughly tested; the flight model of the chopper is now integrated into the flight model of PACS, ready for the HERSCHEL/PLANCK launch in 2008 by an ARIANE5 rocket and the following 5-year mission.

Cryogenic filter- and spectrometer wheels for the Mid Infrared Instrument (MIRI) of the James Webb Space Telescope (JWST)

Following a warm launch in 2013 the MIRI instrument aboard JWST will be operated for a lifetime of 5-10 years in the L2-orbit at a temperature of ~6 K. The main requirements for its three wheel mechanisms include: (1) reliability, (2) optical precision, (3) low power dissipation, (4) high vibration capability, (5) functionality at 4 < T < 300 K. The filter wheel carries broad and narrow band spectral filters, coronographic masks and a prism on its 18 positions. Each of the two spectrometer wheels is equipped with two disks on both sides of a central torque motor, one of them carries 6 gratings, the other a dichroic/mirror arrangement. The optical positions are defined by a ratchet mechanism. No closed loop control is required; therefore the long time average heat dissipation is negligible. A new ratchet mechanism had to be developed to satisfy a 120° increment of only three positions for the spectrometer wheels. Extensive cold and warm tests were performed on the development models of the filter and spectrometer wheels at MPIA. These results stimulated numerous improvements in the mechanical and thermal design which are now to be implemented in the qualification and flight models developed jointly with Carl Zeiss. Synergies are expected from a similar development of the NIRSPEC wheels, in which MPIA and Carl Zeiss are involved.

LINC-NIRVANA, integration of an interferometric and cryogenic camera: first verification results

LINC-NIRVANA is an interferometric imaging camera, which combines the two 8.4 m telescopes of the Large Binocular Telescope (LBT). The instrument operates in the wavelength range from 1.1 μm to 2.4 μm, covering the J, H and K-bands. The beam combining camera (NIRCS) offers the possibility to achieve diffraction limited images with the spatial resolution of a 23 m telescope. This camera, which combines the AO corrected beams of both telescopes, is designed to deliver a 10 arcsec x 10 arcsec diffraction limited field of view. The optics and cryo-mechanics are designed for operation at 60 Kelvin. Equipped with a HAWAII-2 detector mounted on a rotation stage in order to compensate for the sky rotation, a filter wheel and a dichroic wheel to split the light into the science channel and the fringe tracking channel, the camera is fairly large and complex and requires certain features to be considered and tested. The verification of all these components follows a challenging AIV plan. We describe this AIV phase from initial integration of individual units to the final verification tests of the complete system. We report the performance of the cryogenic opto-mechanics and of the science detector. We also demonstrate the functionality of the cryo-mechanics and the cryo-cooling at sub-system level, which represents the current state of integration. Finally, we discuss key elements of our design and potential pros and cons.

LINC-NIRVANA for the LBT: setting up the world's largest NIR binoculars for astronomy

LINC-NIRVANA (LN) is the near-infrared, Fizeau-type imaging interferometer for the Large Binocular Telescope (LBT) on Mt. Graham, Arizona, USA (3267m of elevation). The instrument is currently being built by a consortium of German and Italian institutes under the leadership of the Max Planck Institute for Astronomy (MPIA) in Heidelberg, Germany. It will combine the radiation from both 8.4m primary mirrors of LBT in such a way that the sensitivity of a 11.9m telescope and the spatial resolution of a 22.8m telescope will be obtained within a 10.5arcsec x 10.5arcsec scientific field of view. Interferometric fringes of the combined beams are tracked in an oval field with diameters of 1 and 1.5arcmin. In addition, both incoming beams are individually corrected by LN’s multi-conjugate adaptive optics (MCAO) system to reduce atmospheric image distortion over a circular field of up to 6arcmin in diameter. This paper gives a comprehensive technical overview of the instrument comprising the detailed design of LN’s four major systems for interferometric imaging and fringe tracking, both in the NIR range of 1 - 2.4μm, as well as atmospheric turbulence correction at two altitudes, both in the visible range of 0.6 - 0.9μm. The resulting performance capabilities and a short outlook of some of the major science goals will be presented. In addition, the roadmap for the related assembly, integration and verification (AIV) process will be discussed. To avoid late interface-related risks, strategies for early hardware as well as software interactions with the telescope have been elaborated. The goal is to ship LN to the LBT in 2014.