Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The rapidly evolving hypergiant IRC+10420: High-resolution bispectrum
  speckle-interferometry and dust-shell modelling   The hypergiant IRC+10420 is a unique object for the study of stellar
evolution since it is the only object that is believed to be witnessed in its
rapid transition from the red supergiant stage to the Wolf-Rayet phase. Its
effective temperature has increased by 1000-2000K within only 20yr. We present
the first speckle observations of IRC+10420 with 73mas resolution. A
diffraction-limited 2.11 micron image was reconstructed from 6m telescope
speckle data using the bispectrum speckle-interferometry method. The visibility
function shows that the dust shell contributes 40% to the total flux and the
unresolved central object 60%. Radiative transfer calculations have been
performed to model both the spectral energy distribution and visibility
function. The grain sizes, a, were found to be in accordance with a standard
distribution function, n(a)~a^(-3.5), with 0.005 micron < a < 0.45 micron. The
observed dust shell properties cannot be fitted by single-shell models but seem
to require multiple components. At a certain distance we considered an
enhancement over the assumed 1/r^x density distribution. The best model for
both SED and visibility was found for a dust shell with a dust temperature of
1000K at its inner radius of 69Rstar. At a distance of 308Rstar the density was
enhanced by a factor of 40 and and its density exponent was changed from x=2 to
x=1.7. The shell's intensity distribution was found to be ring-like.The ring
diameter is equal to the inner diameter of the hot shell (69mas). The diameter
of the central star is 1mas. The two-component model can be interpreted in
terms of a termination of an enhanced mass-loss phase roughly 60 to 90 yr (for
d=5kpc) ago.

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The categories of this paper are: comp-gas
14
The categories of this paper are: math-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: cmp-lg
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The categories of this paper are: dg-ga
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The categories of this paper are: q-alg
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The categories of this paper are: nlin
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The categories of this paper are: cs
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The categories of this paper are: plasm-ph
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The categories of this paper are: atom-ph
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The categories of this paper are: cond-mat
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The categories of this paper are: patt-sol
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The categories of this paper are: nucl-ex
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The categories of this paper are: funct-an
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The categories of this paper are: quant-ph
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The categories of this paper are: hep-lat