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Issue A&A
Volume 436, Number 3, June IV 2005
Page(s) 925 - 931
Section Interstellar and circumstellar matter
DOI 10.1051/0004-6361:20042135



A&A 436, 925-931 (2005)
DOI: 10.1051/0004-6361:20042135

A quasi-time-dependent radiative transfer model of OH 104.9+2.4

D. Riechers1, 2, Y. Balega3, T. Driebe2, K.-H. Hofmann2, A. B. Men'shchikov4, V. I. Shenavrin5 and G. Weigelt2

1  Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
    e-mail: riechers@mpia-hd.mpg.de
2  Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
3  Special Astrophysical Observatory, Nizhnij Arkhyz, Zelenchuk district, Karachai-Cherkessian Republic, Russia
4  Institute for Computational Astrophysics, Saint Mary's University, Halifax, NS B3H 3C3, Canada
5  Crimean Astrophysical Observatory, Nauchny, 98409, Crimea, Ukraine

(Received 7 October 2004 / Accepted 8 February 2005 )

Abstract
We investigate the pulsation-phase dependent properties of the circumstellar dust shell (CDS) of the OH/IR star OH 104.9+2.4 based on radiative transfer modeling (RTM) using the code DUSTY. Our previous study concerning simultaneous modeling of the spectral energy distribution (SED) and near-infrared (NIR) visibilities (Riechers et al. 2004) has now been extended by means of a more detailed analysis of the pulsation-phase dependence of the model parameters of OH 104.9+2.4 . In order to investigate the temporal variation in the spatial structure of the CDS, additional NIR speckle interferometric observations in the K' band were carried out 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. Several key parameters of our previous best-fitting model had to be adjusted in order to be consistent with the newly extended amount of observational data. It was found that a simple rescaling of the bolometric flux $F_{\rm bol}$ is not sufficient to take the variability of the source into account, as the change in optical depth $\tau$ over a full pulsation cycle is rather high. On the other hand, the impact of a change in effective temperature  $T_{\rm eff}$ on SED and visibility is rather small. However, observations, as well as models for other AGB stars, show the necessity of including a variation of $T_{\rm eff}$ with pulsation phase in the radiative transfer models. Therefore, our new best-fitting model accounts for these changes.


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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