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Published December 2011 | Published
Journal Article Open

The Cosmic Background Imager 2


We describe an upgrade to the Cosmic Background Imager instrument to increase its surface brightness sensitivity at small angular scales. The upgrade consisted of replacing the 13 0.9-m antennas with 1.4-m antennas incorporating a novel combination of design features, which provided excellent sidelobe and spillover performance for low manufacturing cost. Off-the-shelf spun primaries were used, and the secondary mirrors were oversized and shaped relative to a standard Cassegrain in order to provide an optimum compromise between aperture efficiency and low spillover lobes. Low-order distortions in the primary mirrors were compensated for by custom machining of the secondary mirrors. The secondaries were supported on a transparent dielectric foam cone to minimize scattering. The antennas were tested in the complete instrument, and the beam shape and spillover noise contributions were as expected. We demonstrate the performance of the telescope and the intercalibration with the previous system using observations of the Sunyaev–Zel'dovich effect in the cluster Abell 1689. The enhanced instrument has been used to study the cosmic microwave background, the Sunyaev–Zel'dovich effect and diffuse Galactic emission.

Additional Information

© 2011 The Authors. Monthly Notices of the Royal Astronomical Society © 2011 RAS. Accepted 2011 August 18. Received 2011 August 18; in original form 2011 July 7. Article first published online: 28 Sep 2011. ACT thanks the Royal Society for support via a Dorothy Hodgkin Research Fellowship and a Small Research Grant. ACT also acknowledges an STFC Postdoctoral Research Fellowship. The Royal Society has also supported CBI2 via an International Joint Project Grant awarded to MEJ. JRA acknowledges support by a studentship from the Science and Technology FacilitiesCouncil and a Super Science Fellowship from the Australian Research Council. LB and RB acknowledge support from Center of Excellence in Astrophysics and Associated Technologies (PFB 06), and RB also acknowledges support from ALMA-Conicyt 31080022 and 31070015. CD acknowledges an STFC advanced fellowship and ERC IRG grant under the FP7. We thank the contributing institutions and investigators of the Strategic Alliance for the Implementation of New Technologies (SAINT) for vital financial support of the Chajnantor Observatory. We also thank the Kavli Operating Institute, Barbara and Stanley Rawn Jr, Maxine and Ronald Linde, Cecil and Sally Drinkward, and Rochus Vogt. We thank Matthias Tecza for help with the ZEMAX analysis. Finally, we thank the staff of the Chajnantor Observatory, particularly Cristόbal Achermann, Nolberto Oyarce, José Cortes and Wilson Araya, for expert and untiring support of the operations of CBI.

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