A Lifetime of Influence: Abstracts, Talks, and Posters
 

Where do LBVs Come From? Where do Wolf-Rayet Stars Come From?

Nathan Smith
UC Berkeley

Mass loss plays a critical role of feedback in stellar evolution: by raising a star's M/L ratio with time, it drives the mass-loss rate even higher. Taking current estimates of mass-loss rates in clumped O-star winds as an initial state, Peter and I argued that a simple prescription for this feedback effect can account for the observed properties of WNH stars if they occupy the later phases of core-H burning in luminous stars. In turn, the feedback driven by these strong winds during the WNH phase propels the star close to the Eddington limit, perhaps triggering the onset of the LBV phase.

In order to proceed to the He-rich Wolf-Rayet phase, a massive star must shed its remaining outer H envelope, either through episodic LBV eruptions, dense winds, or mass transfer in close binaries. For initial masses above 40 Msun where RSGs no longer play a role, evidence suggests that episodic LBV eruptions can dominate over line-driven winds in single-star evolution. LBV eruptions are likely to be insenstitive to metallicity, and this has important implications for the existence of WR stars and GRBs in low-metallicity environments. The nature of LBV vs. RSG mass loss has important implications for the range of initial masses that end as WR stars.