CN in prestellar cores

Context. Determining the structure of and the velocity field in prestellar cores is essential to understanding protostellar evolution. Aims. We have observed the dense prestellar cores L 1544 and L 183 in the N = 1 -> 0 rotational transition of CN and (CN)-C-13 in order to test whether CN is depleted in the high-density nuclei of these cores. Methods. We have used the IRAM 30 m telescope to observe along the major and minor axes of these cores. We compare these observations with the 1 mm dust emission, which serves as a proxy for the hydrogen column density. Results. We find that while CN(1- 0) is optically thick, the distribution of 13CN(1- 0) intensity follows the dust emission well, implying that the CN abundance does not vary greatly with density. We derive an abundance ratio of [CN]/[H-2] = 10(-9) in L 183 and 1-3 x 10(-9) in L 1544, which, in the case of L 183, is similar to previous estimates obtained by sampling lower-density regions of the core. Conclusions. We conclude that CN is not depleted towards the high-density peaks of these cores and thus behaves like the N-containing molecules N2H+ and NH3. CN is, to our knowledge, the first C-containing molecule to exhibit this characteristic.