On the Nature of the Herbig B[e] Star Binary System V921 Scorpii: Discovery of a Close Companion and Relation to the Large-scale Bipolar Nebula

Kraus, S., Calvet, N., Hartmann, L., Kreplin, A., Monnier, J. D., Weigelt, G.

The Astrophysical Journal Letters, Vol. 746, Issue 1, id. L2 (2012)


Belonging to the group of B[e] stars, V921 Scorpii is associated with a strong infrared excess and permitted and forbidden line emission, indicating the presence of low- and high-density circumstellar gas and dust. Many aspects of V921 Sco and other B[e] stars still remain mysterious, including their evolutionary state and the physical conditions resulting in the class-defining characteristics. In this Letter, we employ Very Large Telescope Interferometer/AMBER spectro-interferometry in order to reconstruct high-resolution (λ/2Β = 0.0013″) model- independent interferometric images for three wavelength bands around 1.65, 2.0, and 2.3 µm. In our images, we discover a close (25.0 ± 0.8 mas, corresponding to ≈29 ± 0.9 AU at 1.15 kpc) companion around V921 Sco. Between two epochs in 2008 and 2009, we measure orbital motion of ≈7°, implying an orbital period of ≈35 years (for a circular orbit). Around the primary star, we detect a disk-like structure with indications for a radial temperature gradient. The polar axis of this AU-scale disk is aligned with the arcminute-scale bipolar nebula in which V921 Sco is embedded. Using Magellan/IMACS imaging, we detect multi-layered arc-shaped substructure in the nebula, suggesting episodic outflow activity from the system with a period of ≈25 years, roughly matching the estimated orbital period of the companion. Our study supports the hypothesis that the B[e] phenomenon is related to dynamical interaction in a close binary system.

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