IRC+10 216 in action: Present episode of intense mass-loss reconstructed by two-dimensional radiative transfer modeling

Free access article

Issue		A&A Volume 392, Number 3, September IV 2002


Page(s)		921 - 929
Section		Formation, structure and evolution of stars
DOI		http://dx.doi.org/10.1051/0004-6361:20020954

A&A 392, 921-929 (2002)
DOI: 10.1051/0004-6361:20020954

IRC+10 216 in action: Present episode of intense mass-loss reconstructed by two-dimensional radiative transfer modeling

A. B. Men'shchikov, K.-H. Hofmann and G. Weigelt

Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
e-mail: sasha, khh, weigelt@mpifr-bonn.mpg.de
(Received 27 May 2002 / Accepted 20 June 2002 )

Abstract
We present two-dimensional (2D) radiative transfer modeling of IRC+10 216 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+10 216 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 $\dot{M} \approx 10^{-5}$ $M_{\odot}$ yr ^-1 to the rate of $\dot{M} \approx 3 \times 10^{-4}$ $M_{\odot}$ yr ^-1 in 2001. The rapid increase of the mass loss of IRC+10 216 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 $v_{\rm T} \approx 27$ km s ^-1 due to the evaporation of the recently formed dust grains. This self-regulated shift of the dust density peak in the bipolar shell mimics a rapid radial expansion, whereas the actual outflow has probably a lower speed $v < v_\infty \approx 15$ km s ^-1. The model predicts that the star will remain obscured until $\dot{M}$ 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.

Key words: radiative transfer -- circumstellar matter -- stars: individual: IRC+10 216 -- stars: mass-loss -- stars: AGB and post-AGB -- infrared: stars

Offprint request: A. B. Men'shchikov, sasha@mpifr-bonn.mpg.de

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