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Astron. Astrophys. 349, 267-275 (1999)

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The chemical composition of the silicate dust around RAFGL7009S and IRAS 19110+1045 *

K. Demyk 1, A.P. Jones 1, E. Dartois 2,1, P. Cox 1 and L. d'Hendecourt 1

1 IAS-CNRS, Université Paris XI, Batiment 121, F-91405 Orsay Cedex, France
2 IRAM, 300, rue de la Piscine, F-38406 Saint Martin d'Hères, France

Received 18 March 1999 / Accepted 30 June 1999


We have studied the chemical composition of the silicates around the two massive protostellar objects RAFGL7009S (IRAS 18316-0602) and IRAS 19110+1045. The silicate features of both sources are similar. The position and shape of the 9.6 and 18 µm silicate bands coincide with those of amorphous pyroxene-type silicates. We find that the silicate features cannot be reproduced with compact pyroxene grains containing magnesium and iron. An admixture of iron, aluminium and some degree of porosity is necessary to reproduce respectively the red wing of the 18 µm band, the plateau between the two silicate bands and the widths of the bands. The iron is to be found in the form of Fe-rich pyroxenes, also containing small amounts of calcium, and in iron-oxides. Better fits are obtained with aluminium incorporated into the silicate structure (in aluminosilicates) than for aluminium in oxides such as Al2O3. The compositions we propose are in agreement with cosmic elemental abundance constraints. No crystalline material is observed in either source and we find that at most 1-2% of the silicate mass could be crystalline in these sources.

Key words: infrared: ISM: lines and bands – molecular processes – ISM: abundances – ISM: dust, extinction – ISM: molecules – ISM: individual objects: RAFGL7009S – ISM: individual objects: IRAS 19110+1045

* Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA.

Send offprint requests to: K. Demyk (demyk@ias.fr)

© European Southern Observatory (ESO) 1999

Online publication: August 25, 1999