Identification of SH [FORMULA][F]Δv=1[/F][/FORMULA] Ro-vibrational Lines in R Andromedae

We report the identification of SH Deltav=1 ro-vibrational lines in the published high-resolution infrared spectrum of the S-type star R Andromedae. This is the first astronomical detection of this molecule. The lines show inverse P Cygni profiles, indicating infall motion of the molecular layer due to stellar pulsation. A simple spherical shell model with a constant infall velocity is adopted to determine the condition of the layer. It is found that a single excitation temperature of 2200 K reproduces the observed line intensities satisfactorily. SH is located in a layer from 1.0 to approximately 1.1 stellar radii, which is moving inward with a velocity of 9 km s-1. These results are consistent with the previous measurements of CO Deltav=3 transitions. The estimated molecular abundance SH/H is 1x10-7, consistent with a thermal equilibrium calculation.