2006A&A...456..535S

We present a compositional analysis of 8-13µm spectra of 32 young stellar objects (YSOs). Our sample consists of 5 intermediate-mass stars and 27 low-mass stars. Although some previous studies give reasons for the similarity between the dust in circumstellar disks of TTauri stars and Herbig Ae/Be stars, a quantitative comparison has been lacking so far. Therefore, we include a discussion of the results of the 10µm spectroscopic survey of van Boekel et al. (2005A&A...437..189V), who focus on Herbig Ae/Be stars, the higher mass counterparts of TTauri stars, and draw comparisons to this and other studies. While the spectra of our 32 objects and first scientific results have already been published elsewhere we perform a more detailed analysis of the ∼10µm silicate feature. In our analysis we assume that this emission feature can be represented by a linear superposition of the wavelength-dependent opacity κ_abs(λ) describing the optical properties of silicate grains with different chemical composition, structure, and grain size. Determining an adequate fitting equation is another goal of this study. Using a restricted number of fitting parameters, we investigate which silicate species are necessary for the compositional fitting. Particles, with radii of 0.1µm- and 1.5µm and consisting of amorphous olivine and pyroxene, forsterite, enstatite, and quartz are considered. Only compact, homogeneous dust grains are used in the presented fitting procedures. In this context we show that acceptable fitting results can also be achieved if emission properties of porous silicate grains are considered instead. Our analysis shows - in terms of the properties of the circumstellar dust-like crystallinity - TTauri systems are a continuation of HAeBe systems at their lower mass end. However, a weak correlation between grain growth and stellar luminosity could be found, in contrast to HAeBe systems.