Bispectrum speckle interferometry of IRC+10216:
The dynamic evolution of the innermost circumstellar environment from
1995 to 2001
G. Weigelt, Y.Y. Balega, T. Blöcker, K.-H. Hofmann, A.B. Men'shchikov,
J.M. Winters
Astronomy & Astrophysics 392, 131 (2002)
Abstract.
We present new near-infrared (JHK) bispectrum speckle-interferometry
monitoring of the carbon star IRC+10216 obtained between 1999 and
2001 with the SAO 6m telescope. The J-, H-, and K-band resolutions are 50mas,
56mas, and 73mas, respectively. The total sequence of K-band
observations covers now 8 epochs from 1995 to 2001 and shows the dynamic
evolution of the inner dust shell. The present observations show that the
appearance of the dust shell has considerably changed compared to the epochs
of 1995 to 1998. Four main components within a 0.2" radius can be identified
in the K-band images. The apparent separation of the two initially brightest
components A and B increased from ~191mas in 1995 to ~351mas in 2001.
Simultaneously, component B has been fading and almost disappeared in 2000
whereas the initially faint components C and D became brighter (relative to
peak intensity). The changes of the images can be related to changes of the
optical depth caused, for instance, by mass-loss variations or new dust
condensation in the wind. Our recent two-dimensional radiative transfer model
of IRC+10216 suggests that the observed relative motion of components A
and B is not consistent with the outflow of gas and dust at the well-known
terminal wind velocity of 15 km/s. The apparent motion with a deprojected
velocity of 19 km/s on average and of recently 27 km/s appears to be caused
by a displacement of the dust density peak due to dust evaporation in the
optically thicker and hotter environment. The present monitoring, covering
more than 3 pulsation periods, shows that the structural variations are not
related to the stellar pulsation cycle in a simple way. This is consistent
with the predictions of hydrodynamical models that enhanced dust formation
takes place on a timescale of several pulsation periods. The timescale of the
fading of component B can well be explained by the formation of new dust in
the circumstellar envelope.
