dc.contributor.author |
Nagendra, K. N |
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dc.contributor.author |
Leung, C. M |
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dc.date.accessioned |
2008-07-22T11:51:57Z |
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dc.date.available |
2008-07-22T11:51:57Z |
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dc.date.issued |
1996-08 |
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dc.identifier.citation |
Monthly Notices of the Royal Astronomical Society, Vol. 281, No. 4, pp. 1139 - 1164 |
en |
dc.identifier.issn |
0035-8711 |
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dc.identifier.uri |
http://hdl.handle.net/2248/2826 |
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dc.description.abstract |
Radiation transport models are constructed for the dust shells of the hydrogen deficient supergiant star R Coronae Borealis (R CrB). IRAS observations of R CrB are used as constraints in selecting the model parameters. Based on suggestions from earlier work, a double-shell model is employed as a standard configuration for R CrB. The first shell is a hot inner shell of radius 5 arcsec surrounding the central star. The second shell is a cold remnant shell which is highly extended, with a radius of 10 arcmin (derived assuming a source distance of 1.6 kpc). The two shells can be spatially separated, and can have completely different mechanisms for the heating of their dust grains. A detailed parametric study of the system is undertaken using simple power law density and opacity for single sized grains. The models of R CrB clearly point to the configuration of a large well-separated cold dust shell surrounding a tiny hot dust shell, which supports the existing view that this extended shell is a fossil shell. However, the separation between the two shells cannot be determined purely from the radiative transfer modelling. This can still be treated as a free parameter of the system for modelling purposes. The interstellar radiation field (ISRF) incident on the outer boundary of the system plays a considerable role in explaining the 60- and 100-μm surface brightness of R CrB measured by IRAS. The observed constant temperature of the fossil shell, however, poses serious theoretical problems. We propose models in which the density varies as r^-gamma (gamma~=1.0-1.5). The source of dust heating in our models is a combination of central star radiation and ISRF. The amorphous carbon grains seem to give better fits to the IRAS data than the crystalline grains do. A comparison of both the analytic models and the radiative transfer models is made, to clarify their usefulness in modelling the density and the surface brightness data of R CrB. The models are schematic in nature, and are not intended as best fitting models for the R CrB fossil shell. |
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dc.format.extent |
3044398 bytes |
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dc.format.mimetype |
application/pdf |
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dc.language.iso |
en |
en |
dc.publisher |
Royal Astronomical Society |
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dc.relation.uri |
http://adsabs.harvard.edu/abs/1996MNRAS.281.1139N |
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dc.subject |
Radiative transfer |
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dc.subject |
Circumstellar matter |
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dc.subject |
Stars: individuals : R coronae borealis |
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dc.subject |
Dust |
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dc.subject |
Extinction |
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dc.subject |
Infrared:stars |
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dc.title |
Models of highly extended dust shells around R Coronae Borealis |
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dc.type |
Article |
en |