Two-wind interactions in binaries with two orbiting giant stars

Abstract

Some red giant envelopes present spiral structures (seen either in dust-scattered stellar continuum or in molecular line emission), the most striking example probably being AFGL 3068. This object has been modeled (both analytically and numerically) in terms of a wind ejected from a star in orbit around a binary companion. We revisit both analytical models and 3D simulations of a wind from an orbiting red giant star, and extend the numerical simulations to the case of a binary with two red giants with strong winds. We find that most two-wind models on the orbital plane show a ‘double spiral’ structure close to the binary source, and that these two arms merge into a single spiral structure at larger distances. However, for the case of a binary with two identical winds, the two spiral arms are still present at large distances from the binary source. We also find that for models of two (not identical) dynamically important winds, a region close to the orbital plane has material from both winds. Also, an approximately conical region centered on the orbital axis is filled exclusively by the wind with larger momentum rate. These two structures lead to morphologies reminiscent of the so-called ‘hour glass’ planetary nebulae. Finally, we find that increasing wind velocity disparities lead to the formation of clumpy structures along the spiral arms. Observations of ‘clumpy spirals’ are therefore likely to indicate the presence of two strong winds from the stars in the central binary system.

Smoke on the wind: dust nucleation in the archetype colliding-wind pinwheel WR 104

“…By including dust directly in their hydrodynamical modelling, these authors were able to retrieve the realistic density structure of the massive binary WR98a, a system similar to WR104, harbouring a pinwheel nebula . Such spiral patterns have also been observed around massive red giant binary systems, as recently modelled by Castellanos-Ram írez et al ( 2021 ). The binary interaction is also evoked to explain the 3D gaseous structures observed by Atacama Large Millimeter/submillimeter Array (ALMA) around massive stars (Maercker et al 2012 ).…”

Morpho-kinematic Properties of Wolf–Rayet Planetary Nebulae

“…Recent hydrodynamic simulations demonstrate that binary stellar evolution can shape axisymmetric morphologies (e.g., Akashi et al 2015;Akashi & Soker 2016;Chen et al 2016;García-Segura et al 2018, 2021Zou et al 2020;Castellanos-Ramírez et al 2021). It is worthwhile mentioning that magnetohydrodynamic simulations of the envelope of a single AGB star could not support bipolar PNs at physically possible rotating speeds (García-Segura et al 2014).…”

Morpho-kinematics of the circumstellar envelope of the AGB star R Dor: a global view

“…ii) The formation of the bipolar outflows remains unexplained. It may invite interpretations in terms of magnetic fields (García-Segura et al 2005;Winters et al 2022), or in terms of interacting winds in a binary (Nordhaus & Blackman 2006;Castellanos-Ramírez et al 2021), and more specifically in terms of an additional companion orbiting EP Aqr at a distance of ∼10 au (Homan et al 2020), but none of these can be solidly justified. The latter authors present a number of relevant suggestive arguments in relation to the observation of a complex pattern of arcs in the emission of the polar outflows.…”