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Session 53 - SNs, Planetaries and Circumstellar Disks.
Display session, Wednesday, June 10
A crucial parameter in determining the evolution of massive stars is the amount of mass lost through stellar winds. Over the lifetimes of stars with initial masses greater than 25M_ødot, it is expected that mass loss will occur in several stages, in a fast wind during an early O star phase, in a slow wind in an intermediate red supergiant phase (or via eruptions in a Luminous Blue Variable phase) and then during a second fast wind phase when the star enters a Wolf-Rayet phase. Evidence of the mass-loss can be seen in the circumstellar regions of these stars in the form of ring nebulae. Here we present the first CO 1->0 emission-line maps of the vicinities of two Wolf-Rayet stars (WR16 and WR75) and their associated ring nebulae. We illustrate that significant amounts of molecular gas appear associated with these ring nebulae and therefore that the mass of gas in ring nebulae is significantly higher than inferred from observations of the ionized gas component. We discuss the possible stellar and interstellar origins of these molecular materials and the implications for the evolution of massive stars up to the Wolf-Rayet phase.
This work was funded in part by NASA JOVE grant NAG8-264, NASA ADP grant NAG5-2999 and a grant from NASA administered by the American Astronomical Society
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