Silicates in D-type symbiotic stars: an ISO overview

Abstract

We investigate the IR spectral features of a sample of D-type symbiotic stars. Analyzing unexploited ISO-SWS data, deriving the basic observational parameters of dust bands and comparing them with respect to those observed in other astronomical sources, we try to highlight the effect of environment on grain chemistry and physic. We find strong amorphous silicate emission bands at 10 micron and 18 micron in a large fraction of the sample. The analysis of the 10 micron band, along with a direct comparison with several astronomical sources, reveals that silicate dust in symbiotic stars shows features between the characteristic circumstellar environments and the interstellar medium. This indicates an increasing reprocessing of grains in relation to specific symbiotic behavior of the objects. A correlation between the central wavelength of the 10 and 18 micron dust bands is found. By the modeling of IR spectral lines we investigate also dust grains conditions within the shocked nebulae. Both the unusual depletion values and the high sputtering efficiency might be explained by the formation of SiO moleculae, which are known to be a very reliable shock tracer. We conclude that the signature of dust chemical disturbance due to symbiotic activity should be looked for in the outer, circumbinary, expanding shells where the environmental conditions for grain processing might be achieved. Symbiotic stars are thus attractive targets for new mid-infrared and mm observations.

24 pages, 6 figures, 5 tables - to be published in AJ

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Cited by in corpus (12)

• Early-stage young stellar objects in the Small Magellanic Cloud
• Dust and molecular shells in asymptotic giant branch stars - Mid-infrared interferometric observations of R Aql, R Aqr, R Hya, W Hya and V Hya
• The spectral energy distribution of D-type symbiotic stars: the role of dust shells
• Gas and dust spectra of the D' type symbiotic star HD330036
• Shock fronts in the symbiotic system BI Crucis
• The symbiotic star CH Cygni. II. The broad Ly alpha emission line explained by shocks
• The symbiotic star H1-36. A composite model of line and continuum spectra from radio to ultraviolet
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• Notices to investigation of symbiotic binaries V. Physical parameters derived from UBV magnitudes
• Activity and quiescence in galaxies at redshifts 1.4<z<3.5. The role of the starburst temperature
• Rise and fall of silicate dust in RS Ophiuchi following the 2006 eruption
• The symbiotic system AG Draconis. Soft X-ray bremsstrahlung from the nebulae