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Title:
A 10 micron spectroscopic survey of Herbig Ae star disks: grain growth and crystallization
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Authors:
R. van Boekel, University of Amsterdam
M. Min, University of Amsterdam
L.B.F.M. Waters, University of Amsterdam
A. de Koter, University of Amsterdam
C. Dominik, University of Amsterdam
M.E. van den Ancker, European Southern Observatory
J. Bouwman, Max Planck Institut fuer Astronomie Heidelberg
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Abstract:
We present the results of a ground-based spectroscopic survey of Herbig Ae stars in the 10 micrometer spectral region. We performed compositional fits of the spectra based on properties of homogeneous as well as inhomogeneous spherical particles, and derived the mineralogy and typical grain sizes of the dust responsible for the 10 micron emission. Several trends are reported that can constrain theoretical models of dust processing in these systems: i) none of the sources consists of fully pristine dust comparable to that found in the interstellar medium, ii) all sources with a high fraction of crystalline silicates are dominated by large grains, iii) the disks around more massive stars (above 2.5 solar mass, more than 60 solar luminosities) have a higher fraction of crystalline silicates than those around lower mass stars, iv) in the subset of lower mass stars (below 2.5 solar mass) there is no correlation between stellar parameters and the derived crystallinity of the dust. The evidence found in our survey is combined with that of other studies to present a likely scenario of dust processing in Herbig Ae systems. We conclude that the present data favour a scenario in which the crystalline silicates are produced in the innermost regions of the disk, close to the star, and transported outward to the regions where they can be detected by means of 10 micron spectroscopy. Additionally, we conclude that the final crystallinity of these disks is reached very soon after active accretion has stopped.
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