Vol. 540
In section 6. Interstellar and circumstellar matter

Comparative study of CH+ and SH+ absorption lines observed towards distant star-forming regions

by B. Godard et al., A&A 540, A87


The problem of the CH+ abundance in diffuse interstellar clouds has been with us since the work of Bates and Spitzer more than 50 years ago. Basically, this amounts to the fact that CH+ and CH have similar abundances despite the much more rapid destruction rate expected for CH+. It seems likely that this is caused by rapid CH+ formation in shocks or "hot cells" of dissipating turbulence. The work by Godard et al. uses the Herschel/HIFI instrument to compare SH+ with CH+. Building on earlier work with the APEX telescope, this shows that SH+ and CH+ have similar characteristics and, in particular, similar kinematics, which however differ from those of CH and CN. Interestingly also is that the Galactic center ISM has different CH+ SH+ characteristics from the solar neighborhood.