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

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, 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. 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). 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 A and B is not consistent with the 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 adisplacement 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.

11 pages including 6 PostScript figures; also available from http://www.mpifr-bonn.mpg.de/div/ir-interferometry/publications.html; Astronomy & Astrophysics, in press

References in corpus (4)

• Models of circumstellar molecular radio line emission: Mass loss rates for a sample of bright carbon stars
• Smoke Signals From IRC +10216: 1. Milliarcsecond Proper Motions of the Dust
• Diffraction-limited near-IR imaging at Keck reveals asymmetric, time-variable nebula around carbon star CIT 6
• A multi-wavelength study of the oxygen-rich AGB star CIT 3: Bispectrum speckle interferometry and dust-shell modelling

Cited by in corpus (30)

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• 2D Models for Dust-driven AGB Star Winds
• The enigmatic nature of the circumstellar envelope and bow shock surrounding Betelgeuse as revealed by Herschel. I. Evidence of clumps, multiple arcs, and a linear bar-like structure
• ALMA data suggest the presence of a spiral structure in the inner wind of CW Leo
• Dust grains from the heart of supernovae
• Spatially resolving the inhomogeneous structure of the dynamical atmosphere of Betelgeuse with VLTI/AMBER
• The circumstellar envelope of IRC+10216 from milli-arcsecond to arcmin scales
• The size, luminosity and motion of the extreme carbon star IRC+10216 (CW Leonis)
• High-resolution HST/ACS images of detached shells around carbon stars
• Imaging the circumstellar dust around AGB stars with PolCor
• Discovery of multiple dust shells beyond 1 arcmin in the circumstellar envelope of IRC+10216 using Herschel/PACS
• Aperture synthesis imaging of the carbon AGB star R Sculptoris: Detection of a complex structure and a dominating spot on the stellar disk
• HST/NICMOS Imaging Polarimetry of Proto-Planetary Nebulae II: Macro-morphology of the Dust Shell Structure via Polarized Light
• The complex dust formation zone of the AGB star IRC+10216 probed with CARMA 0.25 arcsec angular resolution molecular observations
• Bipolar outflow on the Asymptotic Giant Branch - the case of IRC+10011
• Detection of OH Towards the Extreme Carbon Star IRC+10216
• The VLTI/MIDI view on the inner mass loss of evolved stars from the Herschel MESS sample
• The weather report from IRC+10216: Evolving irregular clouds envelop carbon star
• Mapping the Linearly Polarized Spectral Line Emission around the Evolved Star IRC+10216
• Multi-wavelength diffraction-limited imaging of the evolved carbon star IRC +10216, II
• IRC+10216 in Action: Present Episode of Intense Mass-Loss Reconstructed by Two-Dimensional Radiative Transfer Modeling
• Discovery of a Shell of Neutral Atomic Hydrogen Surrounding the Carbon Star IRC+10216
• Atmospheric molecular blobs shape up circumstellar envelopes of AGB stars
• Surprising detection of an equatorial dust lane on the AGB star IRC+10216
• Dust temperature and density profiles of AGB and post-AGB stars from mid-infrared observations
• IRC+10216's Innermost Envelope -- The eSMA's View
• Discovery of an optical cocoon tail behind the runaway HD 185806
• Near-infrared Integral-field Spectroscopy of the Wind Forming Region of CW Leo