Invited Talk

Carbon Star Dust Features: The 21 and 30 Micron Features

Kevin Volk (Space Telescope Science Institute)

I will review the discovery of, the general properties of, and the proposed carriers for the 30 micron feature observed in carbon stars and carbon-rich post-AGB objects, as well as the 21 micron feature seen only in carbon-rich post-AGB objects. While MgS has generally been thought to be the carrier of the 30 micron feature, there are significant abundance constraints that appear to make this identification unlikely.

As for the 21 micron feature, many carriers have been proposed, some being dust grains and others being molecules, but there is no accepted best candidate. The suggestion of FeO as the carrier by Posch et al. (2005), which was recently supported by Zhang et al. (2009) as the only viable candidate on abundance grounds, seems to me to be impossible on chemical grounds.

I will suggest some future projects that may shed light on the carriers of these features. In particular spectral-polarimetry over the 21 micron feature should determine whether it is a molecular feature or a solid-state feature.

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