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

Abstract

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, L_W ∼3.2 × 10³⁸ erg s^-1, supplied by massive stars to the nebula.