Stellar Prominences

Abstract

I review recent observational and theoretical progress in the study of condensations of cool material trapped in the coronae of rapidly rotating stars. Such condensations were discovered over a decade ago, producing transient moving absorption features in the optical Balmerseries lines. These condensations appear to be in a physical state similar to that of solar prominence material, in the sense that they are sufficiently cool and dense to contain substantial amounts of neutral hydrogen. The strong coronal magnetic fields of the stars in which they occur serve both to confine and to insulate the cool material. The coronal condensations (sometimes dubbed “slingshot prominences”) form at a variety of distances from the star, but are observed to favour formation sites near the Keplerian co-rotation radius. Simple support models involving purely dipolar fields can explain the existence of stable mechanical equilibria for sheet-like prominences in the equatorial plane. More complex field configurations show a wider variety of stable formation sites, both inside the co-rotation radius and out of the stellar equatorial plane.