Modeling Extinction and Infrared Emission from Fractal Dust Grains: Fractal Dimension as a Shape Parameter

1998 ◽  
Vol 501 (1) ◽  
pp. 175-191 ◽  
Author(s):  
Michael E. Fogel ◽  
Chun Ming Leung
Keyword(s):  
Fractal Dimension ◽  
Shape Parameter ◽  
Infrared Emission ◽  
Dust Grains ◽  
Fractal Dust

scholarly journals Non-stoichiometric amorphous magnesium-iron silicates in circumstellar dust shells

2020 ◽  
Vol 644 ◽  
pp. A139
Author(s):  
Hans-Peter Gail ◽  
Akemi Tamanai ◽  
Annemarie Pucci ◽  
Ralf Dohmen
Keyword(s):  
Infrared Emission ◽  
Dust Particles ◽  
Circumstellar Dust ◽  
Expansion Velocity ◽  
Condensation Temperature ◽  
Dust Formation ◽  
Dust Grains ◽  
Dust Shell ◽  
Dust Shells ◽  
Stellar Outflows

Aims. We study the growth of dust in oxygen-rich stellar outflows in order to find out to which extent dust growth models can quantitatively reconcile with the quantities and nature of dust as derived from observations of the infrared emission from circumstellar dust shells. Methods. We use a set of nine well-observed massive supergiants with optically thin dust shells as testbeds because of the relatively simple properties of the outflows from massive supergiants, contrary to the case of AGB stars. Models of the infrared emission from their circumstellar dust shells are compared to their observed infrared spectra to derive the essential parameters that rule dust formation in the extended envelope of these stars. The results are compared with a model for silicate dust condensation. Results. For all objects, the infrared emission in the studied wavelength range, between 6 and 25 μm, can be reproduced rather well by a mixture of non-stoichiometric iron-bearing silicates, alumina, and metallic iron dust particles. For three objects (μ Cep, RW Cyg, and RS Per), the observed spectra can be sufficiently well reproduced by a stationary and (essentially) spherically symmetric outflow in the instantaneous condensation approximation. For these objects, the temperature at the onset of massive silicate dust growth is of the order of 920 K and the corresponding outflow velocity of the order of the sound velocity. This condensation temperature is only somewhat below the vapourisation temperature of the silicate dust and suggests that the silicate dust grows on the corundum dust grains that formed well inside of the silicate dust shell at a much higher temperature. The low expansion velocity at the inner edge of the silicate dust shell further suggests that, for these supergiants, the region inside the silicate dust shell has an only subsonic average expansion velocity, though a high degree of supersonic turbulence is indicated by the widths of spectral lines. Conclusions. Our results suggest that for the two major problems of dust formation in stellar outflows, that is (i) formation of seed nuclei and (ii) their growth to macroscopic dust grains, we are gradually coming close to a quantitative understanding of the second item.

Infrared emission from isolated dust clouds in the presence of very small dust grains

Icarus ◽  
1991 ◽  
Vol 91 (1) ◽  
pp. 7-13 ◽  
Author(s):  
Dariusz C. Lis ◽  
Chun Ming Leung
Keyword(s):  
Infrared Emission ◽  
Dust Grains ◽  
Dust Clouds ◽  
Small Dust

scholarly journals Charging and Growth of Fractal Dust Grains

2008 ◽  
Vol 36 (1) ◽  
pp. 310-314 ◽  
Author(s):  
Lorin S. Matthews ◽  
Truell W. Hyde
Keyword(s):  
Dust Grains ◽  
Fractal Dust

scholarly journals Dust in Planetary Nebulae

1989 ◽  
Vol 131 ◽  
pp. 117-128 ◽  
Author(s):  
Patrick F. Roche
Keyword(s):  
Thermal Emission ◽  
Planetary Nebulae ◽  
Central Star ◽  
Infrared Emission ◽  
Significant Fraction ◽  
Dust Grains ◽  
Ionized Gas ◽  
Total Luminosity

The presence of dust in planetary nebulae can be deduced in several ways - from the observed depletions of condensable elements, internal extinction and, most directly, through the detection of infrared emission from the dust grains. We know that there is a substantial amount of dust in planetary nebulae, and that a significant fraction of the total luminosity emerges in the infrared through thermal emission in most objects. However, a number of questions still largely remain unsolved, and perhaps the most pressing of these are that we do not yet have a satisfactory understanding of the ultraviolet, optical or infrared properties of the dust grains and we also do not yet know exactly where the emitting grains are located within the nebulae; for example, are they mixed with the ionized gas, or in neutral inclusions or perhaps in a disk around the central star?

scholarly journals Recurrent Dust Formation by Wolf-Rayet Stars

1991 ◽  
Vol 143 ◽  
pp. 417-420
Author(s):  
P.M. Williams ◽  
K.A. Van Der Hucht ◽  
P.S. Thé ◽  
P. Bouchet ◽  
G. Roberts
Keyword(s):  
Dust Emission ◽  
Infrared Emission ◽  
Circumstellar Dust ◽  
Stellar Winds ◽  
Dust Formation ◽  
Dust Grains

A number of Wolf-Rayet stars show variations of up to a factor of ten in their infrared emission on timescales of months to years while their photospheric luminosities remain unchanged. This can be interpreted in terms of variation in the rates at which dust grains form in their stellar winds. Our data show variable circumstellar dust emission from WR 70 (HD 137603), with an episode of enhanced dust formation in early 1989, and fading of emission by dust formed around WR 48a (in 1979) and WR 19 some time before our first observation in 1988. We consider their relation to WR 140 (HD 193793), which forms dust in its wind for a few months at intervals of 7.94 years.

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