Low-state magnetic structures in polars: Nature or nurture

Abstract

We present an orbit-resolved study of the magnetic cataclysmic variable (MCV) BL Hyi in its low state, and we explore the origin of its Ha emission line components, their properties, and their possible formation mechanism.We tentatively associate one of the line components with a high-velocity component also seen in the high state.We propose a scenario in which streaming prominence-like magnetic loops (super-prominences) are kept in place by magnetic field interactions between thewhite dwarf and the donor star and are responsible for the high-velocity line components in the Balmer lines.We also discuss how this is in accord with the standard scenario of the secular evolution for MCVs. Finally, we offer an observational test of our ideas and present challenges for future theoretical studies. © 2010. The American Astronomical Society. All rights reserved.