2008A&A...480L...5H

Determining the structure of and the velocity field in prestellar cores is essential to understanding protostellar evolution. We have observed the dense prestellar cores L 1544 and L 183 in the N=1->0 rotational transition of CN and ¹³CN in order to test whether CN is depleted in the high-density nuclei of these cores. We have used the IRAM 30m 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. 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]/[H₂]=10^–9 in L 183 and 13x10^–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. 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.