This paper describes the key design features and performance of HARP, an innovative heterodyne focal-plane array
receiver designed and built to operate in the submillimetre on the James Clerk Maxwell Telescope (JCMT) in Hawaii.
The 4x4 element array uses SIS detectors, and is the first sub-millimetre spectral imaging system on the JCMT. HARP
provides 3-dimensional imaging capability with high sensitivity at 325-375 GHz and affords significantly improved
productivity in terms of speed of mapping. HARP was designed and built as a collaborative project between the
Cavendish Astrophysics Group in Cambridge UK, the UK-Astronomy Technology Centre in Edinburgh UK, the
Herzberg Institute of Astrophysics in Canada and the Joint Astronomy Centre in Hawaii. SIS devices for the mixers were
fabricated to a Cavendish Astrophysics Group design at the Delft University of Technology in the Netherlands. Working
in conjunction with the new Auto Correlation Spectral Imaging System (ACSIS), first light with HARP was achieved in
December 2005. HARP synthesizes a number of interesting features across all elements of the design; we present key
performance characteristics and images of astronomical observations obtained during commissioning.
The eSMA ("expanded SMA") combines the SMA, JCMT and CSO into a single facility, providing enhanced sensitivity
and spatial resolution owing to the increased collecting area at the longest baselines. Until ALMA early
science observing (2011), the eSMA will be the facility capable of the highest angular resolution observations at
345 GHz. The gain in sensitivity and resolution will bring new insights in a variety of fields, such as protoplanetary/
transition disks, high-mass star formation, solar system bodies, nearby and high-z galaxies. Therefore the
eSMA is an important facility to prepare the grounds for ALMA and train scientists in the techniques.
Over the last two years, and especially since November 2006, there has been substantial progress toward
making the eSMA into a working interferometer. In particular, (i) new 345-GHz receivers, that match the
capabilities of the SMA system, were installed at the JCMT and CSO; (ii) numerous tests have been performed
for receiver, correlator and baseline calibrations in order to determine and take into account the effects arising
from the differences between the three types of antennas; (iii) First fringes at 345 GHz were obtained on August
30 2007, and the array has entered the science-verification stage.
We report on the characteristics of the eSMA and its measured performance at 230 GHz and that expected
at 345 GHz. We also present the results of the commissioning and some initial science-verification observations,
including the first absorption measurement of the C/CO ratio in a galaxy at z=0.89, located along the line of sight to the lensed quasar PKS 1830-211, and on the imaging of the vibrationally excited HCN line towards
We discuss the use of the water vapour radiometry technique for atmospheric phase correction as applied to the Atacama Large Millimetre Array (ALMA). The atmospheric conditions derived from site test instrumentation are summarised, and the nature of the phase correction problem quantified. We then present calculations of the expected errors in the radiometrically-corrected atmospheric phase, based on estimates of the radiometer sensitivity. These results indicate how well we need to know the atmospheric structure in order to make accurate phase estimates, and have implications for the meteorological instruments needed on the site. Finally we present the results of simulations of daytime turbulence on the site, and use these to predict the phase fluctuations due to wet and dry air, and discuss their implications for phase correction at Chajnantor.
The Mars Orbiter Camera (MOC) narrow angle system is a 3.5 m focal length camera that has operated for the last five years as part of the Mars Global Surveyor (MGS) Mission. Folded into a total package (including electronics) of less than 1 m length and weighing just over 20 kg, MOC's Ritchey-Chretien optical design is extremely sensitive to primary-to-secondary despace. Because of this, providing proper focus over the range of operational conditions was the primary challenge of the MOC development effort. As initially proposed, the instrument used a graphite-epoxy metering structure to provide a completely athermal system. Given of the sensitivity of the design and large operational temperature range, this turned out not to be realizable. The first fallback from a completely athermal design was to model the response of the system over temperature, and set the detector so the system would be focus over the range of operational conditions. Prototype testing revealed this was also not a workable solution. Late in the development flow, the system was retrofitted with a set of heaters to control focus in flight by application of radial thermal gradients across the primary mirror. Despite the loss of the first copy of the MOC on Mars Observer in 1993, the MOC on MGS has been an outstanding success, returning over 140,000 images of Mars to date and making a number of new discoveries about the planet.
Conference Committee Involvement (1)
Optical Materials and Structures Technologies
4 August 2003 | San Diego, California, United States