Coronal mass transfer in interbinary loops

¹ Universidade dos Açores, Angra do Heroísmo, Açores, Portugal e-mail: miguelf@mail.angra.uac.pt
² Centro de Astrofísica da Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
³ Centro de Física Fundamental, Facultad de Ciencias, Universidad de Los Andes, Apartado Postal 26, La Hechicera, Merida 5251, Venezuela e-mail: cesar@ula.ve
⁴ Space & Atmosphere Research Center, Department of Applied Mathematics, University of Sheffield, Hicks Building, Hounsfield Road, Sheffield, S3 7RH, England, UK e-mail: c.mendoza@sheffield.ac.uk

Received: 30 August 2004
Accepted: 14 December 2004

Abstract

We consider the transfer of coronal mass between the members of a detached binary system along interconnecting rigid magnetic loops. We show that the asymmetry in the gravitational potential drives a flow from the star closer to fill its Roche lobe towards the other star. The loop base pressures, flow velocities and mass fluxes are not externally imposed but are a result of the heating rate along the loop. As the loop heating increases, the base pressures and mass transfer rates increase and the Mach number decreases. If the heating is not uniformly distributed along the loop, but is instead concentrated near one of the stars, then the mass transfer rate either increases or it decreases, and even changes direction, depending on which star the heating is concentrated on. We also discuss the effect of choosing different boundary conditions. Our model predicts mass transfer rates in reasonable agreement with existing observational estimates, but fails to explain the presence of chromospheric material detected between the stars. Additionally, the differential emission measure profile of the loop models is calculated and it is found to be higher in the loop leg close to the secondary star.