"Metallic Magnetospheres"

Presented by Dr. Stan Owocki, Emeritus Professor, from the University of Delaware Department of Physics and Astronomy

Main-sequence B-stars with a strong magnetic field and moderately rapid rotation form "centrifugal magnetospheres" (CMs). Previous work with former AJC fellow Matt Shultz showed that, for CMs of early-type B-stars with Teff ≳ 17 kK, the onset and strength of associated Balmer emission is well explained in terms of a "centrifugal breakout" (CBO) model, in which mass fed into the CM by the star’s radiatively driven stellar wind builds up to a density that is sufficient for centrifugal forces to overwhelm magnetic confinement. But the lack of Hydrogen emission for cooler B stars was an unexplained puzzle. Spurred by a recent Shultz et al. paper identifying a transition star with reduced Balmer emission, the analysis here now argues that the observed diminution and disappearance of Balmer emission for such late B-stars can be explained by the failure of their lower luminosity to drive hydrogen-rich winds; instead they develop an "ion runaway" of heavier metal ions that are the seat of radiative driving, which thus feed a metallic CM (mCM) for which the requisite hydrogen is diminished or even absent. I conclude with a brief discussion of expected physical and observational properties of this new class of metallic magnetospheres.