The dynamical evolution of the fragmented, bipolar dust shell around the carbon star IRC +10 216 . Rapid changes of a PPN-like structure?

Abstract

We present high-resolution J-, H-, and K-band observations and the first H-K color image of the carbon star IRC +10 216. The images were reconstructed from 6 m telescope speckle interferograms using the bispectrum speckle interferometry method. The H and K images with resolutions between 70 mas and 92 mas consist of several compact components within a 0\farcs2 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 +10 216 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 0.79 mu m and 1.06 mu m 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. Based on observations performed with the 6~m telecope at the Special Astrophysical Observatory, Russia.