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, thecore (r{\le}4''=0.12 pc) of the dense galactic starburst NGC 3603,obtained with the Faint Object Spectrograph aboard the refurbishedHubble 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 97950is therefore the densest concentration of very massive stars known inthe Galaxy. The close physical association between O3 and WNL + absstars, as well as the evolution of spectroscopic features, suggests adirect evolutionary link between them. The total output of Lymancontinuum photons from these 14 stars alone accounts for more than 80%of what is required to ionize the surrounding nebula. The very smallradius of the wind-driven bubble surrounding RD 97950 seems at odds withthe tremendous power, L_{W} {\tilde}3.2 {\times} 10^{38}erg s^{-1}, supplied by massive stars to the nebula.