Two Wolf–Rayet stars at the heart of colliding-wind binary Apep

Callingham, J. R.; Crowther, P. A.; Williams, P. M.; Tuthill, P. G.; Han, Yinuo; Pope, Benjamin; Marcote, B.

doi:10.1093/mnras/staa1244

Cited by 26 publications

(53 citation statements)

References 57 publications

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“…This result rules out the possibility of the secondary component being a neutron star or a black holewhich could conceivably drive a spiral plume by gravitational reflex motion, analogous to that witnessed in some mass-losing red giant systems such as AFGL 3068 (Mauron & Huggins 2006) -or that of a single-star dust production mechanism driving the prominent spiral nebula. This conclusion is supported by the findings of Callingham et al (2020), in which an analysis of the visible-infrared spectrum taken with XSHOOTER on the VLT found that the central engine consists of two WR stars of subtypes WC8 and WN4-6b, respectively, identifying Apep as the first double classical WR binary to be observationally confirmed.…”

Section: Detection Of Apep's Central Binarysupporting

confidence: 64%

“…To indicate the impact of this on the interpretation, we adjust our earlier ∼6:1 K-band binary flux ratio now recognizing the brighter component flux should be split two ways: a stellar photosphere and resolved dust shell. Performing this decomposition, we find that the embedded point sources are left with an approximately equal flux ratio (∼14 per cent of the total flux in each): a result that can be more neatly brought into accord with expectations from spectroscopic evidence (Callingham et al 2019(Callingham et al , 2020.…”

Section: Filter Namementioning

confidence: 51%

“…The apparent fluxes may be influenced by local non-uniform opacity and/or thermal re-radiation from dust, so that the contrast ratios presented in the previous section may not correspond directly to the two stars. This might permit, for example, a more nearly equal binary in luminosity as anticipated for a WR + WR (Callingham et al 2019(Callingham et al , 2020 despite the contrast data in Table 2.…”

Section: Fitting To Visibility Data -1-component Modelmentioning

confidence: 88%

“…The K-band absolute magnitudes of WC8 and WN4-6b stars are typically −5.3 ± 0.5 and −4.6 ± 0.7, respectively (Rate & Crowther 2020). Given the spectral types classified by Callingham et al (2020) and the positional assignment of the two stars based on Marcote et al (in preparation; assuming the WN component launches a larger wind momentum), we expect the flux ratio of the two photospheres to be between 0.2 and 1.6. To achieve a contrast ratio of 6 ± 2intheK band, we require dust centred near the WC component to contribute approximately between 50 per cent and 80 per cent of the total flux.…”

Section: Detection Of Apep's Central Binarymentioning

confidence: 99%

“…Spectroscopic studies have estimated that the distance of Apep is 2.4 +0.2 −0.5 kpc (Callingham et al 2019), which was more recently revised to 2.0 +0.4 −0.3 kpc (Callingham et al 2020). If we were to assume the most recent distance estimate and the binary separation discussed in Section 3, we derive a physical WR binary separation of 95 +19 −14 au at the time of NACO observations (corrected for projection).…”

Section: Enclosed Mass and Distance To Apepmentioning

confidence: 99%

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

Han

Tuthill

Lau

et al. 2020

Monthly Notices of the Royal Astronomical Society

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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 2-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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Section: Detection Of Apep's Central Binarysupporting

confidence: 64%

Section: Filter Namementioning

confidence: 51%

Section: Fitting To Visibility Data -1-component Modelmentioning

confidence: 88%

Section: Detection Of Apep's Central Binarymentioning

confidence: 99%

Section: Enclosed Mass and Distance To Apepmentioning

confidence: 99%

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

Han

Tuthill

Lau

et al. 2020

Monthly Notices of the Royal Astronomical Society

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UV spectropolarimetry with Polstar: massive star binary colliding winds

St-Louis

Gayley

Hillier³

et al. 2022

Astrophys Space Sci

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The winds of massive stars are important for their direct impact on the interstellar medium, and for their influence on the final state of a star prior to it exploding as a supernova. However, the dynamics of these winds is understood primarily via their illumination from a single central source. The Doppler shift seen in resonance lines is a useful tool for inferring these dynamics, but the mapping from that Doppler shift to the radial distance from the source is ambiguous. Binary systems can reduce this ambiguity by providing a second light source at a known radius in the wind, seen from orbitally modulated directions. From the nature of the collision between the winds, a massive companion also provides unique additional information about wind momentum fluxes. Since massive stars are strong ultraviolet (UV) sources, and UV resonance line opacity in the wind is strong, UV instruments with a high resolution spectroscopic capability are essential for extracting this dynamical information. Polarimetric capability also helps to further resolve ambiguities in aspects of the wind geometry that are not axisymmetric about the line of sight, because of its unique access to scattering direction information. We review how the proposed MIDEX-scale mission Polstar can use UV spectropolarimetric observations to critically constrain the physics of colliding winds, and hence radiatively-driven winds in general. We propose a sample of 20 binary targets, capitalizing on this unique combination of illumination by companion starlight, and collision with a companion wind, to probe wind attributes over a range in wind strengths. Of particular interest is the hypothesis that the radial distribution of the wind acceleration is altered significantly, when the radiative transfer within the winds becomes optically thick to resonance scattering in multiple overlapping UV lines.

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The non-thermal emission from the colliding-wind binary Apep

Palacio

Benaglia

Becker

et al. 2022

Publ. Astron. Soc. Aust.

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Therecently discovered massive binary system Apep is the most powerful synchrotron emitter among the known Galactic colliding-wind binaries. This makes this particular system of great interest to investigate stellar winds and the non-thermal processes associated with their shocks. This source was detected at various radio bands, and in addition the wind-collision region was resolved by means of very-long baseline interferometric observations. We use a non-thermal emission model for colliding-wind binaries to derive physical properties of this system. The observed morphology in the resolved maps allows us to estimate the system projection angle on the sky to be $\psi \approx 85^\circ$ . The observed radio flux densities also allow us to characterise both the intrinsic synchrotron spectrum of the source and its modifications due to free–free absorption in the stellar winds at low frequencies; from this, we derive mass–loss rates of the stars of $\dot{M}_\mathrm{WN} \approx 4\times10^{-5}\;\mathrm{M}_\odot\,\mathrm{yr}^{-1}$ and $\dot{M}_\mathrm{WC} \approx 2.9\times10^{-5}\;\mathrm{M}_\odot\,\mathrm{yr}^{-1}$ . Finally, the broadband spectral energy distribution is calculated for different combinations of the remaining free parameters, namely the intensity of the magnetic field and the injected power in non-thermal particles. We show that the degeneracy of these two parameters can be solved with observations in the high-energy domain, most likely in the hard X-rays but also possibly in $\gamma$ -rays under favourable conditions.

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Two Wolf–Rayet stars at the heart of colliding-wind binary Apep

Cited by 26 publications

References 57 publications

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

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

UV spectropolarimetry with Polstar: massive star binary colliding winds

The non-thermal emission from the colliding-wind binary Apep

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