The Dense Galactic Starburst NGC 3603. I. HST/FOS Spectroscopy of Individual Stars in the Core and the source of Ionization and Kinetic Energy

We present spectrograms of 14 individual luminous stars in RD 97950, the core (r≤4"=0.12 pc) of the dense galactic starburst NGC 3603, obtained with the Faint Object Spectrograph aboard the refurbished Hubble Space Telescope. In a volume of less than a cubic light year, three luminous hydrogen-rich WNL+abs stars cohabit with six O3 stars [including two O3 III (f*)] and other early O stars; RD 97950 is therefore the densest concentration of very massive stars known in the Galaxy. The close physical association between O3 and WNL + abs stars, as well as the evolution of spectroscopic features, suggests a direct evolutionary link between them. The total output of Lyman continuum photons from these 14 stars alone accounts for more than 80% of what is required to ionize the surrounding nebula. The very small radius of the wind-driven bubble surrounding RD 97950 seems at odds with the tremendous power, LW ∼3.2 × 10³⁸ erg s⁻¹, supplied by massive stars to the nebula.