EDP Sciences
Free access
Volume 365, Number 3, January III 2001
Page(s) 476 - 490
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20000144

A&A 365, 476-490 (2001)
DOI: 10.1051/0004-6361:20000144

ISO spectroscopy of circumstellar dust in 14 Herbig Ae/Be systems: Towards an understanding of dust processing

G. Meeus1, L. B. F. M. Waters2, 1, J. Bouwman2, M. E. van den Ancker2, 3, C. Waelkens1 and K. Malfait1

1  Astronomical Institute, KU Leuven, Celestijnenlaan 200B, 3001 Heverlee, Belgium
2  Astronomical Institute "Anton Pannekoek", University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
3  Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 42, Cambridge, MA 02138, USA

(Received 9 August 2000 / Accepted 16 October 2000 )

We present Infrared Space Observatory (ISO) spectra of fourteen isolated Herbig Ae/Be (HAEBE) stars, to study the characteristics of their circumstellar dust. These spectra show large star-to-star differences, in the emission features of both carbon-rich and oxygen-rich dust grains. The IR spectra were combined with photometric data ranging from the UV through the optical into the sub-mm region. We defined two key groups, based upon the spectral shape of the infrared region. The derived results can be summarized as follows: (1) the continuum of the IR to sub-mm region of all stars can be reconstructed by the sum of a power-law and a cool component, which can be represented by a black body. Possible locations for these components are an optically thick, geometrically thin disc (power-law component) and an optically thin flared region (black body); (2) all stars have a substantial amount of cold dust around them, independent of the amount of mid-IR excess they show; (3) also the near-IR excess is unrelated to the mid-IR excess, indicating different composition/location of the emitting material; (4) remarkably, some sources lack the silicate bands; (5) apart from amorphous silicates, we find evidence for crystalline silicates in several stars, some of which are new detections; (6) PAH bands are present in at least 50% of our sample, and their appearance is slightly different from PAHs in the ISM; (7) PAH bands are, with one exception, not present in sources which only show a power-law continuum in the IR; their presence is unrelated to the presence of the silicate bands; (8) the dust in HAEBE stars shows strong evidence for coagulation; this dust processing is unrelated to any of the central star properties (such as age, spectral type and activity).

Key words: circumstellar matter -- stars: pre-main sequence -- infrared: ISM: lines and bands -- solar system: formation

Offprint request: G. Meeus gwendolyn@ster.kuleuven.ac.be

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