A PRECISE MEASUREMENT OF THE COSMIC BACKGROUND-RADIATION AT 1.32 MILLIMETERS

A precise value of the cosmic background radiation temperature at 1.32 mm has been determined from the interstellar absorption lines of the CN molecule toward HD 154368. Equivalent widths for CN and 13CN in the main cloud are reported. A very weak secondary cloud has been discovered. Millimeter observations at 2.64 mm revealed weak CN emission from the main cloud with TR* =19.0 ± 5.1 mK. Thus there is some local excitation of CN. Correcting for this yields TCBR = 2.832 ± 0.072 K at 1.32 mm which when combined with the result of Meyer et al. gives the TCBR = 2.831 ± 0.056 K at 1.32 mm. At 2.64 mm, we find TCBR = 2.834 ± 0.085 K.