Bispectrum speckle interferometry of IRC +10216: The dynamic evolution of the innermost circumstellar environment from 1995 to 2001
1
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany e-mail: bloecker@mpifr-bonn.mpg.de; hofmann@mpifr-bonn.mpg.de; sasha@mpifr-bonn.mpg.de;
2
Special Astrophysical Observatory, Nizhnij Arkhyz, Zelenchuk region, Karachai–Cherkesia 35147, Russia e-mail: balega@sao.ru
Corresponding author: G. Weigelt, weigelt@mpifr-bonn.mpg.de
Received:
7
May
2002
Accepted:
17
June
2002
We present new
near-infrared (JHK) bispectrum speckle-interferometry monitoring
of the carbon star IRC+10216 obtained between 1999 and 2001
with the SAO 6 m telescope.
The J-, H-, and K-band resolutions are
50 mas, 56 mas, and 73 mas, 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 ~191 mas in 1995 to ~351 mas 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-1. The apparent motion with
a deprojected velocity of 19 km s-1 on average and of recently
27 km s-1 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.
Key words: techniques: image processing / circumstellar matter / stars: individual: IRC +10216 / stars: mass–loss / stars: AGB and post-AGB / infrared: stars
© ESO, 2002