A Telescope for Observations of the Cosmic Background Radiation Anisotropy
Session 5 -- Cosmology and Gravitational Lenses
Display presentation, Monday, 9:20-6:30, Heller Lounge Room

## [5.18] A Telescope for Observations of the Cosmic Background Radiation Anisotropy

H. T. Nguyen, G. S. Griffin, J. B. Peterson (Princeton University), G. S. Tucker (UBC)

During December 1992 and January 1993 we observed the 2.7K Cosmic Background Radiation using a 1.2 meter cassegrain telescope at the South Pole. The telescope has a beam size (full width at half maximum) of 11 arc-minutes, and scans the sky in a cone of full angle 28 arcminutes. We observed five interlocking circles near RA 23h 05m, Dec. -74 deg 51m., a region relatively free of both Galactic thermal dust emission and Galactic free-free emission. The angular scale 28 arcminutes is an important one to study since the most extensively examined models of the universe predict very different CBR anisotropies at this scale.

Our instrument includes a new type of 100 mK bolometer, a single-mode waveguide design. This design allows us to use a corrugated feed horn, with very low side lobe response, but provides the sensitivity of a broad band bolometer. Our bolometer operates in the 90 Ghz atmospheric window, where Galactic emission has a deep minimum. Because we use this window, we believe that our observations will have substantially less interference from Galactic emission than other observations at similar angular scale.

Other observations of the CBR on similar angular scale show ambiguous results. Some seem to show anisotropy as large as $4 \times 10 ^{-5}$ while others seem to show anisotropy less than $2 \times 10^{-5}$. However, all these observations are either at low frequency, 20-30 GHz, where Galactic free-free emission is expected to exceed $10^{-5}$ T$_{CBR}$ or at high frequency, 180-270 GHz, where Galactic thermal dust emission is expected to exceed $10^{-5}$ T$_{CBR}$.

We will describe the instrument and summarize the status of the data analysis program.