A Telescope for Observations of the Cosmic Microwave Background Anisotropy
Session 77 -- Cosmic Background Radiation
Oral presentation, Thursday, 2:30-4:00, Dwinelle 145 Room

## [77.06] A Telescope for Observations of the Cosmic Microwave Background Anisotropy

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

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

Our instrument uses 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 an 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 scales.

Other observations of the CMB 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.