EDP Sciences
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Volume 424, Number 1, September II 2004
Page(s) 165 - 177
Section Interstellar and circumstellar matter
DOI http://dx.doi.org/10.1051/0004-6361:20040352

A&A 424, 165-177 (2004)
DOI: 10.1051/0004-6361:20040352

High-resolution near-infrared speckle interferometry and radiative transfer modeling of the OH/IR star OH 104.9+2.4

D. Riechers1, Y. Balega2, T. Driebe1, K.-H. Hofmann1, A. B. Men'shchikov1, 3 and G. Weigelt1

1  Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
    e-mail: [riechers;driebe;weigelt]@mpifr-bonn.mpg.de
2  Special Astrophysical Observatory, Nizhnij Arkhyz, Zelenchuk district, Karachai-Cherkessian Republic, Russia
3  Institute for Computational Astrophysics, Saint Mary's University, Halifax, Canada

(Received 27 February 2004 / Accepted 18 May 2004)

We present near-infrared speckle interferometry of the OH/IR star OH 104.9+2.4 in the K' band obtained with the 6 m telescope of the Special Astrophysical Observatory (SAO). At a wavelength of $\lambda = 2.12~\mu$m the diffraction-limited resolution of 74 mas was attained. The reconstructed visibility reveals a spherically symmetric, circumstellar dust shell (CDS) surrounding the central star. The visibility function shows that the stellar contribution to the total flux at $\lambda = 2.12~\mu$m is less than ~50%, indicating a rather large optical depth of the CDS. The azimuthally averaged 1-dimensional Gaussian visibility fit yields a diameter of 47 $\pm$ 3 mas (FHWM), which corresponds to 112 $\pm$ 13 AU for an adopted distance of $D = 2.38 \pm 0.24$ kpc. To determine the structure and the properties of the CDS of OH 104.9+2.4 , radiative transfer calculations using the code DUSTY were performed to simultaneously model its visibility and the spectral energy distribution (SED). We found that both the ISO spectrum and the visibility of OH 104.9+2.4 can be well reproduced by a radiative transfer model with an effective temperature $T_{\rm eff} = 2500 \pm 500$ K of the central source, a dust temperature $T_{\rm in} = 1000 \pm 200$ K at the inner shell boundary $R_{\rm in}
\simeq 9.1\,R_{\star} = 25.4\,$ AU, an optical depth $\tau_{2.2~ \mu \rm m} = 6.5 \pm 0.3$, and dust grain radii ranging from $a_{\rm min} = 0.005 \pm 0.003~\mu$m to $a_{\rm max} = 0.2 \pm 0.02~\mu$m with a power law $n(a) \propto a^{-3.5}$. It was found that even minor changes in $a_{\rm max}$ have a major impact on both the slope and the curvature of the visibility function, while the SED shows only minor changes. Our detailed analysis demonstrates the potential of dust shell modeling constrained by both the SED and visibilities.

Key words: radiative transfer -- stars: AGB and post-AGB -- stars: mass-loss  -- stars: circumstellar matter -- infrared: stars -- stars: individual: OH 104.9+2.4

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© ESO 2004