2010A&A...521L..24D

Using Herschel's HIFI instrument, we observe [CII] along a cut through S140, as well as high-J transitions of CO and HCO⁺ at two positions on the cut, corresponding to the externally irradiated ionization front and the embedded massive star-forming core IRS1. The HIFI data were combined with available ground-based observations and modeled using the KOSMA-τ model for photon-dominated regions (PDRs). We derive the physical conditions in S140 and in particular the origin of [CII] emission around IRS1. We identify three distinct regions of [CII] emission from the cut, one close to the embedded source IRS1, one associated with the ionization front, and one further into the cloud. The line emission can be understood in terms of a clumpy model of PDRs. At the position of IRS1, we identify at least two distinct components contributing to the [CII] emission, one of them a small, hot component, which can possibly be identified with the irradiated outflow walls. This is consistent with the [CII] peak at IRS1 coinciding with shocked H₂ emission at the edges of the outflow cavity. We note that previously available observations of IRS1 can be reproduced well by a single-component KOSMA-τ model. Thus, it is HIFI's unprecedented spatial and spectral resolution, as well as its sensitivity that has allowed us to uncover an additional hot gas component in the S140 region.