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.

Herschel/PACS observations of the 69μm band of crystalline olivine around evolved stars

“…From the width versus peak position diagram (Fig. 3), we find a temperature in agreement with the 100−200 K range by Angeloni et al (2007). As for the other disk sources, it is positioned above the pure forsterite curve.…”

“…HDE 330036 is a D' type symbiotic star, the evolutionary stage following the post-AGB (Jorissen et al 2005). Crystalline olivine bands were detected at 19.7, 23.7, and 33.6 µm, and pyroxenes at 15.9, 20.7, and 26.1 µm in the ISO-SWS spectrum by Angeloni et al (2007). They find that the crystalline silicates reside in a circumbinary disk at a temperature close to 100−200 K. Our 69 µm detection of the forsterite is relatively strong with a peak strentgh of 8.5% over the continuum.…”

Eccentricity-pumping in post-AGB stars with circumbinary discs

“…Dust discs are increasingly being identified around the central stars of planetary nebulae, e.g. NGC 2346 for which eclipses from a dusty disc have been detected (Costero et al 1986;Miszalski et al 2011), as well as in some symbiotic stars (Angeloni et al 2007) and hydrogen-deficient binary (Netolický et al 2009). Around some silicate J-type stars the disc is resolved (Deroo et al 2007), but only one system shows evidence for binarity (Izumiura et al 2008).…”

“…The detection of cool (from about 100 to 150 K) oxygenrich crystalline silicate dust grains (Waters et al 1998) as well as the presence of large (sub-micron) grains are other indications of the long-lived nature of these discs (e.g. Angeloni et al 2007;Gielen et al 2008). In some cases, Keplerian rotation is detected at least in the inner disc region (Bujarrabal et al 2005).…”

Shock fronts in the symbiotic system BI Crucis

“…The modelling of line and continuum spectra makes use of suma , 1 a code that simulates the physical conditions of an emitting gaseous nebula under the coupled effect of photoionization from an external source and shocks. The important role of dust is investigated following Angeloni et al (2007a,b,c).…”