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N. Smith (University of Colorado)
The most prodigious mass loss for luminous hot stars occurs during the Luminous Blue Variable (LBV) phase in transition to a Wolf-Rayet star, because the most luminous hot stars never become red supergiants. LBVs differ from other luminous stars in that most of the mass loss and virtually all of the dust formation that they experience happens as a result of a few short-duration eruptions, rather than in a steady wind. In some ways, dust formation during LBV outbursts is similar to novae, where a hot central engine heats the ejected dust shell, making many LBVs bright mid-IR sources and forming large dust grains. The most observable example of this is the nebula around Eta Carinae, which contains more than 10 solar masses of material, while nebulae around the eclipsing binary RY Scuti and other LBVs share similar but less extreme properties. These evolved stars eject CNO-processed material -- in the case of Eta Car, nearly all of the CNO is nitrogen. The orders-of-magnitude depletion of C and O may weigh heavily upon the dust composition and the gas-to-dust mass ratio, usually assumed in order to measure the mass of their nebulae from thermal-IR emission. This is exacerbated by the fact that all LBV nebulae show bright infrared [Fe II] emission, indicating that much of the iron is in the gas phase. Understanding the properties of dust in these nebulae is important for evaluating the pre-supernova mass loss in massive stars, and because their dusty N-rich material will mix with the eventual supernova ejecta when the central star explodes.
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Bulletin of the American Astronomical Society, 37 #2
© 2005. The American Astronomical Soceity.