Observational Constraints on The Evolution of Dust in ...

90 Spitzer Survey of Protoplanetary Disk Dust in Serpens
Figure 4.7 – IRS spectra of the disk sources in Serpens, contd.
are indeed tracers of grain size. The relationship is much tighter for the 10 µm feature,
as also seen by the great spread in the correlation for the 20 µm feature.
Following their procedure, we first subtracted the continuum of each spectrum by
fitting a second-order polynomial to the following regions: blueward of the 10 µm
feature, between the 10 and the 20 µm features, and redward of the 20 µm feature
(6.8–7.5, 12.5–13.5 and 30–36 µm). The peak fluxes at 9.8, 10, 11.3, 19, 20, and 23.8
µm were then determined (see Table 4.2). Figure 4.9 shows the results for our sample
of disks, excluding those with PAH emission. The best fit found by Kessler-Silacci et
al. (2006) for the c2d IRS first look sample of YSOs has been indicated for comparison
(solid line). The agreement of the Serpens data with the best fit of Kessler-Silacci et
al. (2006) is excellent, and more evident for the 10 µm than for the 20 µm feature
due to the larger scatter in the latter group.
Olofsson et al. (2009) generated synthetic 10 µm features calculated for different
grain sizes and compositions. Their models are generated for amorphous silicates
of olivine and pyroxene stoichiometry and a 50:50 mixture, with grain size varying