All the class B sources are carbon rich proto-planetary nebulae (PPNe).
A PPN is an evolved transitional object that ceased violent mass loss
in the AGB phase, but the central star has not become hot enough to
ionize the circumstellar material to form a planetary nebula (Kwok
[1993]). The class B sources are certainly a minor population
of the UIR objects. However, we consider the class B sources as the
key to understand the open questions on the creation and evolution of
UIR carrier because a PPN is one of the main sites of dust formation.
It is also interesting to note that there is a sample of PPNe that has
isolated 3.3 m band without 3.4
m emission as The Red
Rectangle (HD 44179) (Tokunaga et al. [1991]). There is also
large scattering in the intensity of 3.4
m band relative to
3.3
m band in those PPNe classified in class B.
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Figure 1: The spectral sequence of QCC along with temperatures of thermal annealing. The emission and absorption spectra are shown in the left and the middle panels, respectively, in the order of annealing temperature; as-deposited, 600, 700, 723, 740, 760, 823, and 873 K from the top to the bottom. The spectra of several PPNe are shown in the right panel for comparison adapted from Joblin et al. ([1996]), Geballe et al. ([1992]), and Tokunaga et al. ([1991]) |
We infer the spectral diversity of PPNe is the link to connect class B
spectral features with class A. We searched for a laboratory analog of
carbon material which has spectral flexibility required to reproduce
the variation of PPNe spectra. Sakata et al. ([1990]), Dischler
et al. ([1983]), and Bounouh et al. ([1995]) demonstrated
that the intensity of the 3.4 m absorption band decreases relative
to the 3.3
m band in amorphous carbon material by heating. Scott &
Duley ([1996]), and Scott et al. ([1997]) also reported the
similar thermal alteration in the absorption and emission features
of hydrogenated amorphous carbon (HAC) prepared by laser ablation of
graphite. We produced QCC films with a plasma vapor deposition technique
developed by Sakata et al. ([1984]) which intends to mimic the
carbon dust solidification in expanding carbon rich stellar
atmosphere. In this paper, we investigated the effect of thermal
annealing on QCC in terms of emission and absorption spectra. We compare
the spectral sequence of thermally annealed QCC with the spectral
variation of PPNe in the 3
m region to discuss the circumstellar
evolution of carbon dust.
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