A multiline study of the Cepheus B cloud

Abstract

Following up on our previous low-resolution studies (Beuther et al. 2000; Mookerjea et al. 2006) in the nearby star forming region Cepheus B, we try to understand photo-induced chemistry of the photon dominated regions (PDRs) using the higher resolution data observed with the IRAM 30 m telescope at Pico Veleta. The aim of our study is to resolve the temperature, chemical, and excitation structure of the transition zone from the H ii region to the dense molecular cloud in a PDR which is subject only to moderately strong UV fields. We study two cuts running through the interfaces into the main cloud and thus allow to trace several interface regions. Particularly, we select two positions at the interface for a more detailed study. The studied frequency ranges from 85 GHz to 272 GHz and includes 21 transitions of 11 molecules such as HCN, HCO +, CN, CS, CCH, and CCS. Combined with the low - J CO maps in this region (Ungerechts et al. 2000), we calculate the integrated intensity distribution along the cuts and line ratios between different tracers and transitions. H column density along the cuts has been estimated under the Local Thermodynamic Equilibrium (LTE) assumption. The integrated line intensities present nice changes from the H ii region into the molecular clouds. There is an enhancement of all the tracers at the two interface positions. © 2008 EAS EDP Sciences.