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J. K. Cartwright, S. Padin, T. J. Pearson, A. C. S. Readhead, M. C. Shepherd (California Institute of Technology), G. B. Taylor (National Radio Astronomy Observatory)
We describe polarization observations of the CMBR with the Cosmic Background Imager, a 13 element interferometer which operates in the 26-36 GHz band from a site at 5000m in northern Chile. The array consists of 90-cm Cassegrain antennas mounted on a single, fully steerable platform; this platform can be rotated about the optical axis to facilitate polarization observations. The CBI employs single mode circularly polarized receivers, of which 12 are configured for LCP and one is configured for RCP. The 12 cross polarized baselines sample multipoles from l~600 to l~3500. The instrumental polarization of the CBI was calibrated with observations of 3C279, a bright polarized source which is unresolved by the CBI. Because the centimeter flux of 3C279 is variable, it was monitored twice per month for 8 months in 2000 with the VLA at 22 and 43 GHz. These observations also established the stability of the polarization characteristics of the CBI. This work was made possible by NSF grant AST-9802989