Detection of magnetic fields in both B-type components of the $\epsilon$ Lupi system: a new constraint on the origin of fossil fields?

TL;DR

This study reports the first detection of magnetic fields in both stars of the $ ext{epsilon}$ Lupi binary system, providing new insights into the origin of fossil magnetic fields in massive stars.

Contribution

It presents the first observation of magnetic fields in both components of an early-type binary, offering new constraints on fossil magnetic field formation theories.

Findings

Magnetic fields detected in both binary components.

Magnetic axes are approximately anti-aligned.

Magnetospheres are likely interacting.

Abstract

High-resolution circular spectropolarimetric observations, obtained with ESPaDOnS in the context of the BinaMIcS Large Program, have revealed a magnetic field in the B3V secondary component of the SB2 binary system $\epsilon$ Lupi (B2/B3). As the B2V primary is already known to be magnetic, this is the first detection of a magnetic field in both components of an early-type binary system. The longitudinal magnetic field of the primary is $\sim -200$ G; that of the secondary $\sim +100$ G. Observations can be approximately reproduced by a model assuming the magnetic axes of the two stars are anti-aligned, and roughly parallel to their respective rotation axes. Estimated magnetospheric radii indicate a high probability that their magnetospheres are interacting. As many of the arguments for the different proposed formation scenarios of fossil magnetic fields rely upon evidence drawn from investigations of close binaries, in particular the rarity of magnetic ABO stars in close binaries and the previous absence of any known close binary with two magnetic, massive stars, this discovery may be an important new constraint on the origin of fossil magnetic fields.