title: A large coronal loop in the Algol system.
abstract: The close binary Algol system contains a radio-bright KIV subgiant star in a very close (0.062 astronomical units) and rapid (2.86 day) orbit with a main sequence B8 star. Because the rotation periods of the two stars are tidally locked to the orbital period, the rapid rotation drives a magnetic dynamo. A large body of evidence points to the existence of an extended, complex coronal magnetosphere originating at the cooler K subgiant. The detailed morphology of the subgiant's corona and its possible interaction with its companion are unknown, though theory predicts that the coronal plasma should be confined in a magnetic loop structure, as seen on the Sun. Here we report multi-epoch radio imaging of the Algol system, in which we see a large, persistent coronal loop approximately one subgiant diameter in height, whose base is straddling the subgiant and whose apex is oriented towards the B8 star. This suggests that a persistent asymmetric magnetic field structure is aligned between the two stars. The loop is larger than anticipated theoretically, but the size may be the result of a magnetic interaction between the two stars.
authors.affiliation: Department of Physics and Astronomy, University of Iowa, Van Allen Hall, Iowa City, Iowa 52240, USA.
authors.forename: W M
authors.initials: WM
authors.lastname: Peterson
authors.forename: R L
authors.initials: RL
authors.lastname: Mutel
authors.forename: M
authors.initials: M
authors.lastname: Güdel
authors.forename: W M
authors.initials: WM
authors.lastname: Goss