Title:The 10 micron feature of Herbig Ae/Be candidates from the Pico dos Dias 
Survey

Abstract:
Herbig Ae/Be (HAeBe) objects are intermediate mass (2-10 M_sun) stars in the 
pre-main sequence. Some of their properties remain not well understood to date. 
Only a full multi-wavelength study is able to reveal the general properties of 
their circumstellar material.

We propose a method of characterizing the circumstellar environment of such 
objects by a two-step strategy. First, the dust chemistry is constrained by a 
compositional fit of the silicate feature. Once the disk opacity is determined, 
the spectral energy distribution (SED) is then modeled with the flared disk 
model proposed by Dullemond et al. (2001).

The preliminary results of the first step are shown in the present work. We 
have adopted the position unbiased sample of HAeBe candidates detected by the 
Pico dos Dias Survey (Vieira et al . 2003), to study the silicate feature from 
ISO observations. We have determined the dust grain fractions from fit of the 
10 micron feature, with a combination of commonly adopted dust grain opacities. 
We have also studied its shape and correlation with the infrared spectral 
slope.

We conclude that the amorphous carbon can be responsible for an important 
fraction of the dust grain composition, in spite of being neglected in previous 
similar studies (van Boekel et al. 2005; Bouwman et al. 2008). Besides, the 
studied 10 micron features follow an evolutionary sequence (from amorphous 
material absorption to crystalline grain emission), as previously reported by 
Kessler-Silacci et al. (2005).

Our perspectives are to develop a SED automatic fitting tool, that uses the 
already derived dust opacities as an input. We also plan to extend our sample, 
in order to perform a statistical analysis of HAeBe disk properties.