ABUNDANCES OF THE HEAVY-ELEMENTS IN THE MAGELLANIC CLOUDS .2. H-II REGIONS AND SUPERNOVA-REMNANTS

This paper presents the first consistent abundance analysis of both H II regions and supernova remnants in the Magellanic Clouds, as derived from detailed modeling of spectra extending from 3000 to 11000 A. The major purpose of the investigation was to find the zero-point error that might exist between the separated abundance scales derived from supergiants (from Russell and Bessell) and H II regions, and thereby determine the first consistent abundance scale from helium to the heaviest elements. An overlap between the two abundance scales was provided by the observation of supernova remnants. Detailed modeling of both the H II regions and the supernova remnants was performed using the same generalized modeling code MAPPINGS (Binette et al.), thus providing a consistent physical framework for both. For elements heavier than argon, however, a differential analysis was performed between the supernova remnants and the Galactic Herbig-Haro (H-H) objects. This shows that there is no measurable zero-point error between the abundance scales of the supergiants and the H II regions. This result is crucial and allows us, for the first time, to connect the two scales and thereby determine important details of the past star formation histories of both the Magellanic Clouds and the Galaxy. The most exciting result is that the elemental abundances relative to iron in the Clouds match those of the present local interstellar medium more closely than that of the Sun itself, thus suggesting a close similarity between the star formation histories of the Magellanic Clouds and of the local interstellar medium. Conversely, this indicates that the local interstellar medium of the Sun 4.5 × 109 yr ago had a substantially different history of star formation.