Observational Constraints on The Evolution of Dust in ...

84 Spitzer Survey of Protoplanetary Disk Dust in Serpens
Figure 4.2 – IRS spectra of the embedded sources in Serpens with rising mid-IR spectra. The
prominent ice absorption features (at 6.0, 6.85, 7.7, 9.0 and 15.2 µm) are marked, together with the
silicate absorption feature at 9.7 µm. The object number is indicated at the top right of each panel.
as absorption features in the wavelength range of the IRS instrument (e.g., Boogert
et al. 2004).
Of our sample, 21 sources have spectra consistent with embedded sources. These
spectra are shown in Figure 4.2. The most prominent ice feature, CO 2 at 15.2 µm,
can readily be seen in all spectra. Weaker features, such as H 2 O at 6.0 and 6.85 µm
and CH 3 OH at 9.7 µm, need high S/N. Those features are detected in objects 26, 27,
28, 44, 45, 47, 49, 67, 72, 73, 135 and 140. As can be seen in Figure 4.1, the embedded
objects seem to be concentrated in high extinction regions (A V ∼ 10 − 15 mag).
The embedded objects observed as part of the c2d IRS 2nd Look Program have
been studied in detail in a series of papers on ices around YSOs (H 2 O in Boogert et
al. 2008; CO 2 in Pontoppidan et al. 2008; CH 4 at 7.7 µm in Öberg et al. 2008; and
NH 3 at 9.0 µm and CH 3 OH in Bottinelli et al. 2010) and are not discussed further in
this paper.