AAS 206th Meeting, 29 May - 2 June 2005
Session 32 Highlights in Laboratory Astrophysics
Poster, Wednesday, 10:00am-7:00pm, Thursday, 9:20am-2:00pm, June 1, 2005, Ballroom A

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[32.11] The 6.8 \mum band is caused by CaO grains

Y. Kimura, J. A. Nuth III (Astrochemistry Lab., Solar System Exploration Div., NASA's GSFC)

Protostellar objects have several significant infrared. In this study, we will concentrate on the band observed at 6.8 \mum, one of the most obscure features in young stellar objects (YSOs) and one that is only observed in young stellar objects. Although several materials have been proposed to explain this feature, each of these candidates requires specific environmental conditions to explain the observations. We believe that a complex of CaO and Ca(OH)2 could explain observations of a 6.8 \mum feature in protostellar systems.

We discuss the condensation of CaO grains and the formation of a Ca(OH)2 surface layer. The smoke samples were observed using a transmission electron microscope at the University of New Mexico. The infrared spectra of our samples had characteristic dual peaks centered at 6.8 um which was produced by absorption in CaO combined with absorption by a Ca(OH)2 layer on the surface of the CaO grains, produced by reaction with moisture upon exposure to air. The infrared spectra are compared with the spectra of fifteen YSOs. We note that CaO-rich grains are seen in all meteoritic CAIs (calcium-aluminum-rich inclusions), characteristic components of carbonaceous chondrites that must have been produced in the solar nebula. In addition, since CaO has a number of nebular formation routes, CaO could be present in young stellar environments to a significantly higher degree than would be implied by its abundance in meteorites. Moreover, the 6.8 \mum feature has only been observed in YSOs. Therefore, we believe that CaO grains (together with Ca(OH)2 coatings of varying thickness) are a plausible candidate to explain the 6.8 \mum features seen in YSOs and hypothesize that they are produced in the hot interiors of young stellar environments.

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Bulletin of the American Astronomical Society, 37 #2
© 2005. The American Astronomical Soceity.