A measurement at the first acoustic peak of the cosmic microwave background with the 33-GHz interferometer

This paper presents the results from the Joddrell Bank-Instituto de Astrofi scia de Canarias (IAC) two-element 33-GHz interferometer operated with an e lement separation of 32.9 wavelengths and hence sensitive to 1 degrees-scal e structure on the sky. The level of cosmic microwave background (CMB) fluc tuations, assuming a flat CMB spatial power spectrum over the range of mult ipoles l = 208 +/- 18. was found using a likelihood analysis to be Delta T- l = 63(-6)(+7) mu K at the 68 per cent confidence level, after the subtract ion of the contribution of monitored point sources. Other possible foregrou nd contributions have been assessed and are expected to have negligible imp act on this result.