Документ взят из кэша поисковой машины. Адрес оригинального документа : http://star.arm.ac.uk/~ambn/abstract186.ps Дата изменения: Fri Aug 16 13:53:19 1996 Дата индексирования: Mon Oct 1 23:34:22 2012 Кодировка: Поисковые слова: annular solar eclipse

A study of the size and composition of dust grains
in the circumstellar envelope of IRC + 10 o 216
S. Bagnulo, J.G. Doyle and I.P. Griffin
We utilise a modelling technique in which a generalised two­stream Eddington
approximation is applied to the problem of the radiative transfer in a spheri­
cally symmetric dust shell. We calculate the emerging flux taking into account
the effect of non­isotropic scattering, absorption and thermal re­emission for a
multiple grain size, multiple grain component distribution.
We have applied our technique to the well known carbon­rich star IRC +
10 o 216; we have considered a model with grains of amorphous carbon and silicon
carbide, and we have studied how different grain size distributions affect the
transport coefficients and the calculated flux.
In agreement with previous works, we reproduce quite well the general spec­
tral characteristics, spanning from – = 0.55 Їm to 2 cm, assuming the dust
envelope composed of small grains (with radius ё 10 \Gamma2 c Їm) of amorphous
carbons.
The presence of silicon carbide cannot be excluded, but it is not required to
explain the feature at 11.4 Їm observed in the IRAS Low Resolution Spectrum:
a one­component model including only amorphous carbons fits both the general
characteristics and the feature at 11.4 Їm.
Key words: stars: circumstellar matter ­ Stars: carbon ­ Stars: individual:
IRC + 10 o 216
1