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arXiv · 2008.05834

The extreme colliding-wind system Apep: resolved imagery of the central binary and dust plume in the infrared

Y. Han·P. G. Tuthill·R. M. Lau·A. Soulain·J. R. Callingham·P. M. Williams·P. A. Crowther·B. J. S. Pope·B. Marcote
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Abstract

The recent discovery of a spectacular dust plume in the system 2XMM J160050.7-514245 (referred to as "Apep") suggested a physical origin in a colliding-wind binary by way of the "Pinwheel" mechanism. Observational data pointed to a hierarchical triple-star system, however several extreme and unexpected physical properties seem to defy the established physics of such objects. Most notably, a stark discrepancy was found in the observed outflow speed of the gas as measured spectroscopically in the line-of-sight direction compared to the proper motion expansion of the dust in the sky plane. This enigmatic behaviour arises at the wind base within the central Wolf-Rayet binary: a system that has so far remained spatially unresolved. Here we present an updated proper motion study deriving the expansion speed of Apep's dust plume over a two-year baseline that is four times slower than the spectroscopic wind speed, confirming and strengthening the previous finding. We also present the results from high-angular-resolution near-infrared imaging studies of the heart of the system, revealing a close binary with properties matching a Wolf-Rayet colliding-wind system. Based on these new observational constraints, an improved geometric model is presented yielding a close match to the data, constraining the orbital parameters of the Wolf-Rayet binary and lending further support to the anisotropic wind model.

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Y. Han, P. G. Tuthill, R. M. Lau, A. Soulain, J. R. Callingham, P. M. Williams, P. A. Crowther, B. J. S. Pope, B. Marcote. 2020-08-13. The extreme colliding-wind system Apep: resolved imagery of the central binary and dust plume in the infrared. https://doi.org/10.1093/mnras%2Fstaa2349

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