Infrared Detection of CS in the Hot Core AFGL 2591 with SOFIA/EXES

We have performed a 5-8 μm spectral line survey of the hot molecular core associated with the massive protostar AFGL 2591, using SOFIA/EXES. We have supplemented these data with a ground based study around 4.5 μm using the iSHELL instrument, and 8-13 μm using TEXES, on the IRTF. We present the first detection of ro-vibrational transitions of CS in this source. The absorption lines are centred on average around -10 kms−1. Temperatures for CS, hot 13CO and 12CO v=1-2 agree well and are around 700 K. We derive a CS abundance of 8×10−3 and 2×10−6 with respect to CO and H2 respectively. This enhanced CS abundance with respect to the surrounding cloud, 1×10-8, may reflect sublimation of H2S ice followed by gas-phase reactions to form CS. EXES observations of CS are likely to probe deeply into the hot core, to the base of the outflow. Submillimeter and infrared observations trace different components of the hot core as revealed by the difference in systemic velocities, line widths and temperatures, as well as the CS abundance.