Gas and dust spectra of the D' type symbiotic star HD 330036

Abstract

Aims. We present a comprehensive and self-consistent modelling of the D’ type symbiotic star (SS) HD 330036 from radio to UV. Methods. Within a colliding-wind scenario, we analyse the continuum, line, and dust spectra by means of SUMA, a code that simulates the physical conditions of an emitting gaseous cloud under the coupled effect of ionisation from an external radiation source and shocks. Results. We find that the UV lines are emitted from high-density gas between thestars downstream of the reverse shock, while the optical lines are emitted downstream of the shock propagating outwards from the system. As regards the continuum SED, three shells are identified in the IR, at 850 K, 320 K, and 200 K with radii r = 2.8 × 10 13 cm, 4 × 10 14 cm, and 10 15 cm, respectively, after adopting a distance to Earth of d = 2.3 kpc. Interestingly, all these shells appear to be circumbinary. Analysis of the unexploited ISO-SWS spectrum reveals that both PAHs and crystalline silicates coexist in HD 330036, with PAHs associated to the internal shell at 850 K, and crystalline silicates stored in the cool shells at 320 K and 200 K. Strong evidence that crystalline silicates are shaped in a disk-like structure is derived on the basis of the relative band strengths. Finally, we suggest that shocks can be a reliable mechanism for activating the annealing and the consequent crystallisation processes. Conclusions. We show that a consistent interpretation of gas and dust spectra emitted by SS can be obtained by models that account for the coupled effect of the photoionising flux and of shocks. The VLTI/MIDI proposal recently accepted by ESO aims to verify and better constrain some of our results by means of IR interferometric observations.