The MeerKAT+ project will extend the current MeerKAT Radio Telescope Array at the South African Radio Astronomy Observatory (SARAO) site in the Karoo region of South Africa. In this paper we present the developed methodology, instrumentation, and the current status for verifying the pointing accuracy of a single array telescope using an optical pointing telescope and a detailed Pointing Error Budget (PEB) of the radio telescope structure. We will focus on a description of the developed instrumentation, the measurement software, the testing procedures, the measurement plan based upon them, and the applied steps for data processing and analysis. The obtained results are then correlated directly to the PEB. Furthermore, we relate the acquired results from optical pointing tests to some early radio frequency pointing tests and conclude with a discussion.
GREAT (German REceiver for Astronomy at Terahertz frequencies) has been selected as first-light instrument for the
early science flights of SOFIA, scheduled for early 2009. In its first-light configuration GREAT will allow observations
in two out of three FIR bands: two low frequency channels 1.25-1.5 THz and 1.82-1.92 THz for observations of, e.g.,
highly excited CO and of ionized carbon, and a 2.7 THz channel focusing on the ground-state transition of deuterated
molecular hydrogen HD. A forth channel, centered on the 4.7 THz transition of atomic oxygen will become available
later.
The observatory schedule asks for delivery of the instrument in early 2009. At the time of the conference system level
assembly, integration, and verification (AIV) is ongoing, and we report on the performance of the integrated system.
Shipment to NASA/DAOF (Dryden aircraft operations facility) in Palmdale/California for aircraft integration is currently
planned for mid December 2008.
We report on developments of submillimeter heterodyne arrays for high resolution spectroscopy with APEX. Shortly, we will operate
state-of-the-art instruments in all major atmospheric windows accessible from Llano de Chajnantor. CHAMP+, a dual-color 2×7 element heterodyne array for operation in the 450 μm and 350 μm atmospheric windows is in operation since late 2007. With its
state-of-the-art SIS detectors and wide tunable local oscillators, its cold optics with single sideband filters and with 3 GHz of processed IF bandwidth per pixel, CHAMP+ does provide outstanding observing capabilities. The Large APEX sub-Millimeter Array (LAsMA) is in the final design phase, with an installation goal in 2009. The receiver will operate 7 and 19 pixels in the lower submillimeter windows, 285-375 GHz and 385-520 GHz, respectively. The front-ends are served by an array of digital wideband Fast Fourier Transform spectrometers currently processing up to 32×1.5 (optionally 1.8) GHz of bandwidth. For CHAMP+, we process 2.8 GHz of instantaneous bandwidth (in 16.4 k channels) for each of the 14 pixels.
GREAT, the German REceiver for Astronomy at Terahertz frequencies, is a first generation SOFIA dual channel
heterodyne PI−instrument for high resolution spectroscopy. The system is developed by a consortium of German
research institutes. The receiver will allow simultaneous observations in two out of the following three far−infrared
frequency bands:
* a low−frequency (1.4−1.9 THz) channel for e.g. the fine-structure lines of ionized nitrogen [NII] at 205μm
and ionized carbon [CII] at 158μm;
* a mid−frequency (2.4−2.7 THz) channel for e.g. the 112μm transition of HD; and
* a high−frequency (4.7 THz channel) for the 63 μm fine−structure line of neutral atomic oxygen.
Hot electron bolometers (HEB) mixers provide state of the art sensitivity. A spectral resolving power of up to
108 is achieved with chirp transform spectrometers, and a total bandwidth of 4 GHz at 1 MHz resolution is
reached with wide band acousto-optical spectrometers. The modular concept of GREAT allows to observe with
any combination of two out of the three channels aboard SOFIA. A more complete frequency coverage of the
THz regime by adding additional GREAT channels is possible in the future. The adaptation of new LO−, mixer−
or backend−techniques is easily possible.
We describe details of the receiver and the results of first performance tests of the system at 1.9 THz. As an
outlook to future developments we show first results obtained with phase locking a quantum cascade laser, the
most promising option for future high power local oscillators in the Terahertz regime.
GREAT, the German REceiver for Astronomy at Terahertz frequencies, is a first generation SOFIA dual channel
heterodyne PI-instrument for high resolution spectroscopy. The system is developed by a consortium of German
research institutes. The receiver will allow simultaneous observations in two out of the following three far-infrared
frequency bands:
a 1.4-1.9 THz channel for e.g. the fine-structure line of ionized carbon [CII] at 158μm;
a 2.4-2.7 THz channel for e.g. the 112μm transition of HD; and
a 4.7 THz channel for the 63 μm fine-structure line of neutral atomic oxygen.
Hot electron bolometers (HEB) mixers provide state of the art sensitivity. A spectral resolving power of up to
108 is achieved with chirp transform spectrometers, and a total bandwidth of 4 GHz at 1 MHz resolution is
reached with wide band acousto-optical spectrometers. The modular concept of GREAT allows to observe with
any combination of two out of the three channels aboard SOFIA. A more complete frequency coverage of the
THz regime by adding additional GREAT channels is possible in the future. The adaptation of new LO-, mixer-
or backend-techniques is easily possible. We describe details of the receiver and the results of first performance
tests of the system at 1.9 THz.
CHAMP+, a dual-color 2 × 7 element heterodyne array for operation in the 450 μm and 350 μm atmospheric windows is under development. The instrument, which is currently undergoing final evaluation in the laboratories, will be deployed for commissioning at the APEX telescope in August this year.
With its state-of-the-art SIS detectors and wide tunable local oscillators, its cold optics with SSB filters and with 2 GHz of usable IF bandwidth per pixel, CHAMP+ will provide unmatched observing capabilities for the APEX community. The optics allows for simultaneous observations in both colors. For both sub-arrays a hexagonal arrangement with closest feasible spacing of the pixels on sky (2×Θmb) was chosen, which, in scanning mode, will provide data sampled with half-beam spacing. The front-end is connected to a flexible autocorrelator array with a total bandwidth of 32 GHz and 32768 spectral channels, subdivided into 32 IF bands of 1 GHz and 1024 channels each.
R. Güsten, R. Booth, C. Cesarsky, K. Menten, C. Agurto, M. Anciaux, F. Azagra, V. Belitsky, A. Belloche, P. Bergman, C. De Breuck, C. Comito, M. Dumke, C. Duran, W. Esch, J. Fluxa, A. Greve, H. Hafok, W. Häupl, L. Helldner, A. Henseler, S. Heyminck, L. Johansson, C. Kasemann, B. Klein, A. Korn, E. Kreysa, R. Kurz, I. Lapkin, S. Leurini, D. Lis, A. Lundgren, F. Mac-Auliffe, M. Martinez, J. Melnick, D. Morris, D. Muders, L. Nyman, M. Olberg, R. Olivares, M. Pantaleev, N. Patel, K. Pausch, S. Philipp, S. Philipps, T. Sridharan, E. Polehampton, V. Reveret, C. Risacher, M. Roa, P. Sauer, P. Schilke, J. Santana, G. Schneider, J. Sepulveda, G. Siringo, J. Spyromilio, K.-H. Stenvers, F. van der Tak, D. Torres, L. Vanzi, V. Vassilev, A. Weiss, K. Willmeroth, A. Wunsch, F. Wyrowski
APEX, the Atacama Pathfinder Experiment, has been successfully commissioned and is in operation now. This novel submillimeter telescope is located at 5107 m altitude on Llano de Chajnantor in the Chilean High Andes, on what is considered one of the world's outstanding sites for submillimeter astronomy. The primary reflector with 12 m diameter has been carefully adjusted by means of holography. Its surface smoothness of 17-18 μm makes APEX suitable for observations up to 200 μm, through all atmospheric submm windows accessible from the ground.
We present the first astronomical results from DesertSTAR, a 7 pixel heterodyne array receiver designed for operation in the astrophysically rich 345 GHz atmospheric window. DesertSTAR was constructed for the 10m Heinrich Hertz Telescope located at 3150m elevation on Mt. Graham, Arizona. This receiver promises to increase mapping speed at the HHT by a factor of ~15 over the facility's existing single beam, dual polarization receiver. DesertSTAR uses tunerless, single-ended waveguide SIS mixers to achieve uncorrected receiver noise temperatures of ~60K. The instantaneous bandwidth is 2 GHz, with a 5 GHz Intermediate Frequency, offering 1600 km/s of velocity coverage. Cryogenic isolators are employed between the mixers and low noise amplifiers to assure a flat IF passband. The system uses a Joule-Thompson closed-cycle refrigerator with 180W capacity at 70K and 1.8W capacity at 4K. A novel reflective phase grating is used for Local Oscillator multiplexing, while a simple Mylar beamsplitter is used as an LO diplexer. Optics include only polyethelene mixer lenses and a single, cold, flat mirror, maximizing simplicity for high efficiency and easy optical alignment. The computer controlled bias system provides low noise bias for the SIS junctions, magnets and LNAs through a modular and hardware independent GUI interface, and allows remote operation and monitoring. We present measurements of receiver noise, beam quality, efficiency and stability in addition to astronomical observations obtained during engineering runs at the HHT.
We present the concept for KOSMA's 16 element 1.9 THz heterodyne array
STAR (SOFIA Terahertz Array Receiver) which is being developed for
SOFIA. The instrument will consist of two interleaved sub-arrays of 8
pixels each. Together we will have a 4 × 4 pixel array with a beam spacing on the sky of approximately 1.5 times the beam size of 15 arcsec (FWHM). The receiver is mainly targeted at measuring the fine structure transition of ionized atomic carbon at 1.9 THz (158 microns). STAR's optics setup is modeled after the successful design used in KOSMA's SMART receiver. It will contain a K-mirror type beam rotator, a Martin-Puplett diplexer for LO coupling and an LO multiplexer using imaging Fourier gratings. Complete optical sub-assemblies will be machined monolithically as integrated optics units, to reduce the need for optical alignment. STAR will probably use waveguide mixers with diffusion cooled hot electron bolometers, which are being developed at KOSMA. The receiver backends will be KOSMA Array-AOSs. Local oscillator power will be provided by a backward wave oscillator (BWO), followed by a frequency tripler.
DesertSTAR is a 7 beam, 345 GHz heterodyne array receiver for the Heinrich Hertz Telescope (HHT) on Mt. Graham, AZ. The instrument uses fixed-backshort Superconductor-Insulator-Superconductor (SIS) mixers with a broadband waveguide probe. Instantaneous bandwidths greater than 2 GHz can be achieved over the entire 345 GHz atmospheric window. A cryostat with a Joule-Thompson (JT) mechanical refrigerator allows continuous operation and 1.8W of cooling capacity at 4K, and provides the needed temperature stability for low-noise operation. Local Oscillator (LO) distribution is accomplished with a novel phase grating that yields high efficiency and power uniformity in a hexagonally symmetric geometry. The computer controlled bias system is an evolution of a proven design that is simple and portable to any computer platform. The 2 GHz Intermediate Frequency (IF) bandwidth allows the future addition of a wideband backend optimized for extragalactic observations, with ~1700 km/s of velocity coverage. We present measurements of receiver performance and plans for integration on the HHT.
We present the first results obtained with our new dual frequency SIS array receiver SMART The instrument is operational since September 2001 at the KOSMA 3m telescope on Gornergrat near Zermatt/Switzerland. The receiver consists of two 2×4 pixel subarrays. One subarray operates at a frequency of 490 GHz, the other one at 810 GHz. Both subarrays are pointed at the same positions on the sky. We can thus observe eight spatial positions in two frequencies simultaneously. For the first year of operation we installed only one half of each subarray, i.e. one row of 4 mixers at each frequency.
The receiver follows a very compact design to fit our small observatory. To achieve this, we placed most of the optics at ambient temperature, accepting the very small sensitivity loss caused by thermal emission from the optical surfaces. The optics setup contains a K-mirror type image rotator, two Martin-Puplett diplexers and two solid state local oscillators, which are multiplexed using collimating Fourier gratings. To reduce the need for optical alignment, we machined large optical subassemblies monolithically, using CNC milling techniques. We use the standard KOSMA fixed tuned waveguide SIS mixers with Nb junctions at 490 GHz, and similar Nb mixers with Al tuning circuits at 810 GHz.
We give a short description of the front end design and present focal plane beam maps, receiver sensitivity measurements, and the first astronomical data obtained with the new instrument.
We present a new type of phase grating, the Fourier grating, to be used as local oscillator beam multiplexer in heterodyne receivers. The device has been developed for the SOFIA Terahertz Array Receiver (STAR). In contrast to the binary phase gratings (Dammann gratings), which are being used in many array receivers, our gratings have a smooth surface structure without any sharp edges.
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