SIMBAD references

Recent observations suggest that the behavior of tracer species such as N₂H⁺ and CS is significantly different in regions of high- and low-mass star formation. In the latter, N₂H⁺ is a good tracer of mass, while CS is not. Observations show the reverse to be true in high-mass star formation regions. We use a computational chemical model to show that the abundances of these and other species may be significantly altered by a period of accelerated collapse in high-mass star-forming regions. We suggest that these results provide a potential explanation of the observations, and make predictions for the behavior of other species.