Joint Astrophysics Colloquium

What Binaries tell us about the Luminous Blue Variable Phenomenon

Noel Richardson

Université de Montréal

Luminous Blue Variables (LBVs) are massive stars in a rare, transitionary post-main sequence evolutionary phase. These stars have attained luminosities near the Eddington limit and show variability on timescales from hours to years. I will review some of the unusual observational and theoretical history of these objects amongst the massive stars. In recent years, a few paradoxes have emerged in the study of these objects. First, the binary frequency seems extremely low when compared to the massive, main-sequence O stars. Secondly, these evolved stars were theoretically expected to be slow rotators, but at least a few of these stars are rapidly rotating at 90% critical velocity. I will review recent findings related to the multiplicity issue and detail the variability of the binary systems, and what these properties tell us about the LBV phenomenon. Finally, I will briefly review some recent efforts to understand the LBV variability using both ground-based spectroscopy and photometry and space-based photometry from the Canadian MOST satellite.