Publications
of the
MPIfR Optical & Infrared Interferometry Group

G. Weigelt, T. Blöcker, K.-H. Hofmann, A. Men'shchikov, J.M. Winters, Y.Y. Balega

Bispectrum speckle interferometry of IRC+10216: the dynamic evolution of the circumstellar environment from 1995 to 2001

Astronomische Gesellschaft Abstract Series (AGM 19, P37)
Der kosmische Materiekreislauf
Annual Scientific Meeting of the Astronomische Gesellschaft, Sep 23-28, 2002, Berlin, Germany

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, mas, and 73 mas, resp. 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. 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. These changes can be related to changes of the optical depth caused, e.g., by mass-loss variations or new dust condensation in the wind. Our 2D radiative transfer model suggests that the observed relative motion of components A and B is not consistent with the known terminal wind velocity of 15 km/s but appears to be caused by a displacement of the dust density peak due to dust evaporation in the optically thicker and hotter environment. Our 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.