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Issue A&A
Volume 400, Number 3, March IV 2003
Page(s) L21 - L24
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20030141



A&A 400, L21-L24 (2003)
DOI: 10.1051/0004-6361:20030141

Letter

Grain growth in the inner regions of Herbig Ae/Be star disks

R. van Boekel1, 2, L. B. F. M. Waters2, 3, C. Dominik2, J. Bouwman4, A. de Koter2, C. P. Dullemond5 and F. Paresce1

1  European Southern Observatory, Karl-Schwarzschildstrasse 2, 85748 Garching bei München, Germany
2  Astronomical Institute "Anton Pannekoek", University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
3  Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200B, 3001 Heverlee, Belgium
4  CEA, DSM, DAPNIA, Service d'Astrophysique, CEN Saclay, 91191 Gif-sur-Yvette Cedex, France
5  Max-Planck-Institut für Astrophysik, Karl-Schwarzschildstrasse 1, Postfach 1317, 85748 Garching bei München, Germany

(Received 19 September 2002 / Accepted 2 February 2003)

Abstract
We present new mid-infrared spectroscopy of the emission from warm circumstellar dust grains in Herbig Ae/Be stars. Our survey significantly extends the sample that was studied by Bouwman et al. (2001). We find a correlation between the strength of the silicate feature and its shape. We interpret this as evidence for the removal of small (0.1  $\mu$m) grains from the disk surface while large (1-2  $\mu$m) grains persist. If the evolution of the grain size distribution is dominated by gravitational settling, large grains are expected to disappear first, on a timescale which is much shorter than the typical age of our programme stars. Our observations thus suggest a continuous replenishment of micron sized grains at the disk surface. If the grain replenishment is due to the dredge-up of dust from the disk interior, the mineralogy we observe is representative of the bulk composition of dust in these stars.


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

Offprint request: R. van Boekel, rvanboek@eso.org

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© ESO 2003


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