Discovery of highly dynamic matter enhancements along the polar axis and equatorial plane in the luminous blue variable binary HD 5980.
VILLAR-SBAFFI A., MOFFAT A.F.J. and ST-LOUIS N.
Abstract (from CDS):
HD 5980 is a W-R+O eclipsing binary in the Small Magellanic Cloud that has attracted considerable attention since it underwent a luminous blue variable (LBV)-type outburst in 1994. Since then, intense spectroscopic and photometric monitoring have revealed the presence of periodic variability on a timescale of 6-7 hr that cannot be explained by our current understanding of the system. In this paper, we present the first results from our polarimetric observations around secondary eclipse when the assumed Wolf-Rayet (W-R) star passes in front of the assumed LBV component (phase φ=0.36). These data confirm the presence of stochastic polarimetric variability on a typical timescale of ∼30 minutes, reaching a very high amplitude of almost 1% on our last of five nights. At that time, we also found that the mass loss, which is responsible for the polarimetric variability, presented fluctuations in axial symmetry ranging from very rapid density enhancements along the orbital plane to polar ejections. We propose that either a fast rotator model for the W-R star or the presence of a close orbiting neutron star could qualitatively explain the observed polarimetric, spectroscopic, and photometric behavior. The evidence presented in this paper is crucial for an understanding of the erratic behavior of this important binary and should be taken into account in any consistent model of the system.
Stars: Binaries: Eclipsing - Polarization - Stars: Individual: Henry Draper Number: HD 5980 - Stars: Mass Loss - Stars: Wolf-Rayet - Techniques: Polarimetric