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Issue A&A Volume 398, Number 2, February I 2003 Page(s) 607 - 619 Section Formation, structure and evolution of stars DOI 10.1051/0004-6361:20021629

A&A 398, 607-619 (2003)
DOI: 10.1051/0004-6361:20021629

Understanding the spectra of isolated Herbig stars in the frame of a passive disk model

C. Dominik¹, C. P. Dullemond², L. B. F. M. Waters^{1, 3} and S. Walch<sup>2

1</sup>  Sterrenkundig Instituut "Anton Pannekoek", Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
    e-mail: dominik@science.uva.nl
²  Max Planck Institut für Astrophysik, Karl Schwarzschild Strasse 1, 85748 Garching, Germany
    e-mail: dullemon@mpa-garching.mpg.de
³  Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200 B, 3001 Heverlee, Belgium

(Received 26 July 2002 / Accepted 7 November 2002)

Abstract
We discuss spectral energy distributions of a sample of Herbig Ae/Be stars in the context of a passive irradiated disk model. The data have been presented earlier by Meeus et al. (2001), and preliminary interpretations of these data were given in that paper. While the spectra of Herbig Ae stars all show similarities, there is significant variation between the spectra, in particular in the shape of the mid-IR rise and in the presence or absence of a silicate feature. We explore the hypothesis that all these different spectra can be interpreted as pure disk spectra without additional components. Using the model of Dullemond et al. (2001) we deduce the disk parameters of a number of the sources, and find that for a large fraction of investigated sources, satisfactory fits can be obtained. The derived model parameters show that some group Ia sources can only be fit with radially increasing surface densities, indicating the presence of depleted inner disk regions. The steep-sloped SEDs of group IIa sources can be fit with very compact disks, probably representing disks with collapsed outer regions. The largest difficulties arise from sources that do not show significant silicate emission features. Our attempts to explain these objects with a pure geometric effect are only partially successful. It seems that these stars indeed require a strong depletion of small silicate grains.

Key words: stars: circumstellar matter -- infrared: stars

Offprint request: C. Dominik, dominik@science.uva.nl

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