The dynamical evolution of the fragmented, bipolar dust shell around the
carbon star IRC+10216:
Rapid changes of a PPN-like structure?
R. Osterbart, Y. Balega, T. Blöcker, A. Men'shchikov and G. Weigelt
Astronomy & Astrophysics 357, 169-176 (2000)
Abstract.
We present high-resolution J-, H-, and K-band observations and
the first H-K color image of the carbon star IRC+10216.
The images were reconstructed from 6 m telescope speckle interferograms
using the bispectrum speckle interferometry method. The H and K images
with resolutions between 70mas and 92mas consist
of several compact components within a 0.2" radius and a fainter
asymmetric nebula. The brightest four components are denoted with A to
D in the order of decreasing brightness in the 1996 image.
A comparison of our images
from 1995, 1996, 1997, and 1998 gives - almost like a movie of five frames
- insight into the dynamical evolution of the inner nebula.
For instance, the separation of the two brightest components A and B
increased from 191 mas in 1995 to 265 mas in 1998. At the same time,
component B is fading and the components C and D become brighter.
The X-shaped bipolar structure of the nebula, most prominently
present in the J-band image, implies an asymmetric mass--loss. Such
asymmetries are often present in protoplanetary nebulae but are
unexpected for AGB stars. IRC+10216 is thus likely to be
very advanced in its AGB evolution, shortly before turning into a
protoplanetary nebula.
The cometary shapes of A in the H and J images and in the 0.79µm
and 1.06µm HST images suggest that the core of A is not the
central star, but the southern lobe of a bipolar structure. The
position of the central star is probably at or near the position of
component B, where the H-K color has a value of 4.2. If the star is
at or near B, then the components A, C, and D are likely to be located
at the inner boundary of the dust shell.
