The Array for Microwave Background Anisotropy (AMiBA) is a radio interferometer for research in cosmology,
currently operating 7 0.6m diameter antennas co-mounted on a 6m diameter platform driven by a hexapod
mount. AMiBA is currently the largest hexapod telescope. We briefly summarize the hexapod operation with
the current pointing error model. We then focus on the upcoming
13-element expansion with its potential
difficulties and solutions. Photogrammetry measurements of the platform reveal deformations at a level which
can affect the optical pointing and the receiver radio phase. In order to prepare for the 13-element upgrade, two
optical telescopes are installed on the platform to correlate optical pointing tests. Being mounted on different
locations, the residuals of the two sets of pointing errors show a characteristic phase and amplitude difference
as a function of the platform deformation pattern. These results depend on the telescope's azimuth, elevation
and polarization position. An analytical model for the deformation is derived in order to separate the local
deformation induced error from the real hexapod pointing error. Similarly, we demonstrate that the deformation
induced radio phase error can be reliably modeled and calibrated, which allows us to recover the ideal synthesized
beam in amplitude and shape of up to 90% or more. The resulting array efficiency and its limits are discussed
based on the derived errors.
Using the array of seven 0.6m antennas in Hawaii, we have conducted short observations on several galaxy clusters through
the Sunyaev-Zeldovich effect at 3mm wavelength in 2007. The observations were done with a resolution of 6', and we
have chosen the low redshift (z=0.09-0.32) massive clusters to optimize detection. Major contamination to the data comes
from instrumental offset and ground pickup. We will demonstrate the results based on a simple on source - off source
switching observing scheme. In addition, the performance of a wideband analog 4-lag correlator was also investigated.
The Academia Sinica, Institute for Astronomy and Astrophysics (ASIAA) is installing the AMiBA interferometric array telescope at the Mauna Loa Observatory, Hawaii. The 6-meter carbon fiber fully steerable platform is mounted on the Hexapod Mount. After integration and equipment with dummy weights, the platform has been measured by photogrammetry to verify its behavior predicted by Finite Element Analysis. The Hexapod servo control is now operational and equipment of the platform with the initial 7 60-cm dishes, the correlator and electronics is underway. Pointing has started with the aid of the optical telescope. We present the status of the telescope after the servo and initial pointing tests have been carried out. We also present the results of platform measurements by photogrammetry.
AMiBA, as a dual-polarization 86-102 GHz interferometer array, is designed to measure the power spectrum of fluctuations in the cosmic microwave background (CMB) radiation, and to detect the high-redshift clusters of galaxies via the Sunyaev-Zel'dovich Effect (SZE). The operation of AMiBA is about to begin after installation of the first two receivers and correlators onto the 6-meter diameter platform by the end of 2005. The initial setup of the array will consist of 7 antennas with 60 cm diameter reflectors in a hexagonal configuration, aiming at multipoles l ~ 3000. Signals from receivers are cross-correlated in analog lag correlators. The initial operation will focus on characterizing the systematics by observing various known objects on the sky. The expansion to 13 elements with larger dishes will commence once the 7-element array testing is completed.