AAS 197, January 2001
Session 42. Dust and Theory of ISM
Display, Tuesday, January 9, 2001, 9:30am-7:00pm, Exhibit Hall

## [42.03] Are Silicon Nanoparticles an Interstellar Dust Component?

A. Li, B.T. Draine (Princeton University Observatory)

Crystalline silicon nanoparticles (SNPs) have been proposed as the source of the Extended Red Emission (ERE) by Ledoux et al. (1998) and Witt et al. (1998). By comparing the observational IR spectrum of NGC 2023 with the predicted IR spectra for pure silicon nano-crystals as well as nano-sized silicon core-SiO2 mantle grains, we show that, if present in quantities sufficient to account for the ERE, silicon nanoparticles would produce a strong emission feature at 16.4\mum (for pure silicon grains), or a strong Si-O vibrational feature at 21\mum (for silicon core-SiO2 mantle grains), neither of which is present in the observed spectrum. If the abundance of SNPs is reduced to the level at which no noticeable IR emission features are produced, the predicted ERE intensity would then be much lower than the observed ERE even assuming 100% photon conversion efficiency. Therefore, SNPs are probably not an important interstellar dust component and are not the ERE agent.

This research was supported in part by NASA grant NAG5-7030 and NSF grant AST-9619429. agli References: Ledoux, G., Ehbrecht, M., Guillois, O., et al. 1998, A&A, 333, L39; Witt, A.N., Gordon, K.D., & Furton, D.G. 1998, ApJ, 501, L111