Publications
of the
MPIfR
Optical & Infrared
Interferometry Group
G. Weigelt and B. Yudin:
The Dust Envelope of R Cas
Astronomy Reports 45, 510-516 (2001)
Abstract.
The spectral energy distribution in the far infrared and the shape of a
broad emission band in the spectrum of R Cas at 9-13 micron can be
reproduced in a model with a dust envelope consisting of approximately
half amorphous olivine (Mg0.8Fe1.2SiO4)
and half amorphous aluminum-oxide grains (Al2O3),
with a small admixture of spinel grains (MgAl2O4).
The dust envelope's optical depth tau(50micron) is 5x10-3
[tau(1.25micron) ~0.07 for agr=0.05micron], and its mass
within r<0.025pc Mdust is 8x10-6Msun. The
index alpha in the power-law radial dust distribution, nd~(Rstar/r)alpha,
is 1.8. Over the last several thousand years, the mass-loss rate of R
Cas has been decreasing as Mdot(t)~t0.2 (where time is
measured backward from the present). This probably implies that R Cas
experienced a thermal helium flare several thousand years ago. If
Mgas/Mdust=200 (where Mgas is the gas mass), the mean mass-loss rate of
the star is 6x10-7Msun/yr.
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