Correlation between grain growth and disk geometry in Herbig Ae/Be systems

¹ Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200B, 3001 Leuven, Belgium e-mail: bram.acke@ster.kuleuven.ac.be
² European Southern Observatory, Karl-Schwarzschild Strasse 2, 85748 Garching bei München, Germany
³ Max-Planck-Institut für Astrophysik, Karl-Schwarzschildstrasse 1, Postfach 1317, 85748 Garching bei München, Germany
⁴ Astronomical Institute “Anton Pannekoek”, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands

Received: 4 February 2004
Accepted: 24 April 2004

Abstract

We have calculated the (sub-)mm spectral indices of 26 Herbig Ae/Be stars, for which we can determine the infrared spectral energy distribution (SED). We find a clear correlation between the strength of the ratio of the near- to mid-infrared excess of these sources, and the slope of the (sub-)mm energy distribution. Based on earlier multi-dimensional modeling of disks around Herbig Ae stars, we interpret this as a correlation between the geometry of the disk (flared or self-shadowed) and the size of the grains: self-shadowed disks have, on average, larger grains than their flared counterparts. These data suggest that the geometry of a young stellar disk evolves from flared to self-shadowed.