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Session 53 - SNs, Planetaries and Circumstellar Disks.
Display session, Wednesday, June 10
The study of circumstellar materials around evolved massive stars leads to the possibility of obtaining information on the history of such stars. In particular, Wolf-Rayet stars are believed to have evolved from massive (>25M_ødot) O star progenitors via a phase of major mass loss (such as a red supergiant or luminous blue variable). The morphology and kinematics of ejected materials may be expected to provide information on the amount of and timescale for mass-loss. In particular, the existence of multiple shells around Wolf-Rayet stars enables the study of the effects of different phases of mass loss. We present high resolution optical imaging and Fabry-Perot observations, made at the Canada-France-Hawaii Telescope (CFHT), of multiple ring nebulae around Wolf-Rayet in the nearby galaxy M33. Our results show: (i) The existence of ejecta shells inside of main sequence shells O star cavities, some of which are almost the same size as the cavities, suggesting ejecta expansion is not necessarily stalled by the hot interior of the progenitor O star bubble. (ii) H\alpha and [OIII] shell kinematics are often dramatically different with [OIII] emission almost exclusively associated with fast-moving Wolf-Rayet wind-blown bubbles inside ejecta materials. (iii) Expanding bubbles of [OIII] emission appear around WN rather than WC subclasses of Wolf-Rayet stars, suggesting "blowouts" of the Wolf-Rayet blown winds towards the end of the WN phase and prior to the WC phase. (iv) Nebulae associated with WC stars are larger than those associated with WN stars, which is consistent with the evolution of Wolf-Rayet stars from WN to WC subtype.
This work was supported in part by a NASA ADP grant NAG5-2999 and by a grant from NASA administered by the American Astronomical Society.
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