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F. Bruhweiler (IACS/CUA), M. Bourdin, R. Freire Ferrero (Strasbourg), T. Gull ((NASA/GSFC/LASP)
The O star, HD 148937, and the O stars of the Rosette Nebula are embedded in extremely young wind-blown interstellar (IS) bubbles. Their kinematic ages are less than 105 yr, much younger than the central O stars. Theoretically, the IS-bubble ages should be the same as that of the central stars. We have analyzed the IUE high-dispersion data for the five central O stars of the Rosette Nebula and new HST/STIS UV spectra for HD 148937 (O 7f) to further constrain the dynamics of the IS-bubbles. These stars have well-determined mass loss rates and wind terminal velocities.
The star HD 148937 is enshrouded in an S-shaped system of knots, NGC6164-5. These knots lie within a apparent very low density cavity. A sharp filamentary shell delineates its boundary. The cavity and the embedded NGC 6164-5 are encompassed by a much larger, nearly circular, H II region. A thin dust shell marks the outer perimeter of the H II region. Very young ages are deduced from the observed cavity radius (5.1 to 14 x 104 yr) and the unusual thinness of the outer dust shell (0.17-1x105 yr). The expansion velocity deduced from the multi-component C IV and Si IV seen in our STIS spectra further supports an extremely young age for the IS-bubble. Previous results reveal the NGC 6164-5 knots to be oxygen deficient. The O-deficiency, if due to pronounced CNO-processing, requires an older, more evolved O star with an age ~ 6 MYR.
In the case of the Rosette Nebula, the inner cavity radius, plus the measured expansion velocity and derived C IV and Si IV column densities deduced from IUE provide a consistent picture and imply an age of only 3.6x104 yrs! This age is, again, far younger than the implied ages of the O stars, 2-3 MYR, in the Rosette. To explain these age discrepancies, we speculate that the winds of the central stars do not immediately form cavities, but drive turbulence in the surrounding H II region. At later times, either due to mass ejection or when the ambient density of the H II region decreases, might actual cavities form.
The author(s) of this abstract have provided an email address for comments about the abstract: bruhweiler@cua.edu