Templates of Binary-induced Spiral-shell Patterns around Mass-losing Post-main-sequence Stars

Abstract

The morphological properties of the outflowing circumstellar envelopes surrounding mass-losing stars in eccentric binary systems are presented from a set of three-dimensional hydrodynamical model simulations. Based on four template models of the envelope viewed for a range of inclination angles of the systems, we implement interpretative tools for observations at high spectral/angular resolutions (as illustrated via velocity channel maps as well as position-velocity, radius-velocity, and angle-radius diagrams). Within this framework, the image and kinematical structures can be used to place constraints on the orbital parameters of the system. Specifically, three unique characteristic patterns in the envelopes are found that distinguish these systems from those in binary systems in circular orbits. Bifurcation of the spiral pattern, asymmetry in the interarm density depression, and a concurrent spiral/ring appearance all point to a binary system with an eccentric orbit. The methodology presented in this paper is illustrated in an analysis of recent radio observations of several asymptotic giant branch stars.

SPH modelling of wind-companion interactions in eccentric AGB binary systems

“…On the one hand, it induces an orbital movement of the stars around their CoM. This generates a spiral shock and significantly beams the wind into the orbital plane resulting in a flattening (Kim & Taam 2012b;Kim et al 2019;El Mellah et al 2020), as is discussed in Sect. 4.1.…”

“…Observations of the eccentric system AFGL3068 reveal spirals that seem to split up (Kim et al 2017). These features are classified as 'bifurcations' and have been shown to be characteristic patterns of eccentric systems (Kim et al 2019). Such bifurcations also appear in the orbital plane morphology of model v20e50, in Fig.…”

“…The simulations are evolved for t max = 93 yrs, corresponding to the required 10 orbital periods, and the outer boundary is set to R bound = 200 au. Previous studies reveal that the four main parameters determining the wind structure are the wind velocity, semi-major axis, mass ratio and eccentricity (Mastrodemos & Morris 1999;Chen et al 2017;Kim et al 2019). In this work, we focus on the impact of the wind speed and eccentricity through the nine models listed in Table 2.…”

Molecular Emissions from Circumstellar Envelopes in the Presence of a Binary Companion

“…5, 6). This interesting property of the spiral pattern induced by the presence of a binary companion in highly elliptical orbit has been remarked early [7,8] and could help to explain the presence of concentric but offset arcs observed at high angular resolution by millimeter interferometric telescopes in some circumstellar envelopes such as IRC+10216 [14,16]. The change in morphology of the envelope might be more clearly appreciated in the angle -radius plot of the systemic velocity channel shown in Fig.…”

“…Although different mechanisms have been proposed, the presence of a binary companion [5,6] is regarded as the most viable cause of the observed unusual morphological features. Several groups have carried out hydrodynamic simulations with different geometrical configurations to study the effect of the binary companion on the structure of the envelopes [2][3][4]7,8]. We emphasize here that in order to compare theoretical predictions with available high angular resolution observations of molecular emission, radiative transfer calculations have been considered.…”