Following our previous work on the hydrodynamic simulations of the structure of circumstellar envelopes in the presence of a binary companion, in this paper we present the results of radiative transfer calculations for molecular emission line HC3N J=5 – 4 from these simulated circumstellar envelopes. We show that the molecular line emission traces closely the spiral pattern and the associated density enhancement induced by the presence of the binary companion. The molecular emission provides the spatial kinematics of the features within the envelope, which is valuable for estimating the orbital parameters of the binary system and for inferring the physical conditions of the gas within the envelope. We also show that the appearance of the molecular emission depends on the viewing angle resulting in a range of shapes from the spiral pattern to ring-like features, similar to that observed recently in a number of circumstellar envelopes at high angular resolution.

Shapes of circumstellar envelopes around mass losing stars contain information of the very inner region of the envelope where mass loss process takes place. It’s well known that the presence of a binary companion leads to strong influence on the structure of the envelope through orbital motion of the mass losing star and the gravitational interaction of the companion with the stellar wind. To investigate this effect and structures of envelopes, we have performed high resolution hydrodynamic simulations of a wide binary system in a number of orbital configurations. Our simulations clearly show the importance of the equation of state of the gas because in isothermal case the width of the spiral arm is significantly broadened with respect to the ideal gas case, therefore resulting in unrealistic spiral patterns. As the orbital geometry changes from circular to elliptical, our simulation results show that the spiral becomes bifurcated and increasingly asymmetric as indicated in previously published results. In the polar direction, the prominent alternating arcs associated with circular orbital configuration morph into almost continuous circular rings. The physical condition of the gas in the envelope is shown to vary strongly between the spiral arm and inter-arm regions. Our hydrodynamic simulations will be useful to interpret high angular resolution observations of circumstellar envelopes.