The early evolution of massive stars: Radio recombination line spectra

Velocity shifts and differential broadening of radio recombination lines are used to estimate the densities and velocities of the ionized gas in several hypercompact and ultracompact H II regions. These small H II regions are thought to be at their earliest evolutionary phase and associated with the youngest massive stars. The observations suggest that these H II regions are characterized by high densities, supersonic flows, and steep density gradients, consistent with accretion and outflows that would be associated with the formation of massive stars.