MILLIMETRIC GROUND-BASED OBSERVATIONS OF COSMIC MICROWAVE BACKGROUND ANISOTROPY

First results of a cosmic microwave background (CMB) anisotropy experi ment conducted at the Observatorio del Teide (Tenerife, Spain) are pre sented. The instrument is a four channel (3.1, 2.1, 1.3, and 1.1 mm) H e-3 bolometer system coupled to a 45 cm diameter telescope. The result ant configuration is sensitive to structures on angular scales similar to 1 degrees-2 degrees. We use the channels at the two highest freque ncies for monitoring the atmosphere and apply a simple method to subtr act this contribution in channels 1 (3.1 mm) and 2 (2.1 mm). The most intense structure at these two frequencies is the Galactic crossing, w ith peak amplitudes of similar to 350 mu K. These crossings have been clearly detected with the amplitude and shape predicted. This demonstr ates that our multifrequency observations allow an effective assessmen t and subtraction of the atmospheric contribution. In the section of d ata at high Galactic latitude we obtain sensitivities similar to 40 mu K beam(-1). The statistical analyses show the presence of common sign als between channels 1 and 2. Assuming a simple Gaussian autocorrelati on model with a scale of coherence theta(c) = 1.32 degrees for the sig nal, a likelihood analysis of this section of data reveals the presenc e of fluctuations with intrinsic amplitude C-0(1/2) = 76(-32)(+42)mu K (with a 68% confidence limit including an similar to 20% calibration uncertainty). Since residual atmospheric noise might still contaminate our results, we also give our result as an upper limit of 118 mu K at a 95% confidence limit.