CS observations of the hotspot at the S 155/Cepheus B interface

We have used the IRAM 30-m telescope to map, in the J=2–1, J=3–2 and J=5–4 rotational transitions of CS, the molecular hotspot located south-east of the Cepheus OB3 association, at the interface that divides the S 155 diffuse Hii region from the Cepheus B molecular cloud. We have also used the FCRAO 13.7-m telescope to map the larger scale CS(2– 1) emission. The ' 1′ × 1′ segment that has been mapped at higher spatial resolution with the 30-m telescope covers four radio continuum sources, one of which (source A) is a blister– type Hii region. By using the CS molecule we analyse: i) the molecular density at the interface region and ii) the kinematics of the molecular gas at the front. The observations confirm that the blister has created a cavity at the edge of the molecular hotspot and is bounded on its sharp side by a dense mlecular front in pressure equilibrium with the ionized gas. The near–IR star at the centre of the blister (A-NIR) is responsible for its ionization and for the heating of the hotspot.