Publications
of the
MPIfR
Optical & Infrared
Interferometry Group
A. Men'shchikov, K.-H. Hofmann, and G.
Weigelt:
IRC+10216 in Action: Present Episode of
Intense
Mass-Loss Reconstructed by Two-Dimensional Radiative Transfer Modeling
Astronomy & Astrophysics, 392, 921 (2002)
Abstract.
We present two-dimensional (2D) radiative transfer modeling of
IRC+10216 at
selected moments of its evolution in 1995--2001, which correspond to
three
epochs of our series of 8 near-infrared speckle images (Osterbart et
al. 2000,
Weigelt et al. 2002). The high-resolution images obtained over the last
5.4 years
revealed the dynamic evolution of the subarcsecond dusty environment of
IRC+10216
and our recent time-independent 2D radiative transfer modeling
reconstructed
its physical properties at the single epoch of January 1997
(Men'shchikov et al. 2001). Having documented the complex changes in
the
innermost bipolar shell of the carbon star, we incorporate the
evolutionary
constraints into our new modeling to understand the physical reasons
for the
observed changes. The new calculations show that our previous static
model is
consistent with the brightness variations seen in the near-infrared
images,
implying that during the last 50 years, we have been witnessing an
episode of a
steadily increasing mass loss from the central star, from Mdot
~ 10^-5
Msun/yr to the rate of Mdot ~ 3x10^-4 Msun/yr
in 2001.
The rapid increase of the mass loss of IRC+10216 and
continuing time-dependent dust formation and destruction caused the
observed
displacement of the initially faint components C and D and of the
bright cavity
A from the star which has almost disappeared in our images in 2001.
Increasing
dust optical depths are causing strong backwarming that leads to higher
temperatures in the dust formation zone, displacing the latter outward
with a
velocity v_T ~ 27 km/s due to the evaporation of the recently
formed dust grains. This self-regulating shift of the dust density peak
in the
bipolar shell mimics a rapid radial expansion, whereas the actual
outflow has
probably a lower speed v < v_inf ~ 15 km/s. The
model
predicts that the star will remain obscured until Mdot starts
to drop back
to lower values in the dust formation zone; in a few years from that
moment, we
could be witnessing the star reappearing.
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