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

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.

arXiv commentThis article has been accepted for publication in the Monthly Notices of the Royal Astronomical Society. 17 pages, 9 figures, 6 tables

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• Nested Dust Shells around the Wolf-Rayet Binary WR 140 observed with JWST
• Radiation-driven acceleration in the expanding WR140 dust shell
• Revealing Efficient Dust-Formation at Low Metallicity in Extragalactic Carbon-Rich Wolf-Rayet Binaries
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