The Dust Condensation Sequence at Low Metallicity: AGB Stars in NGC 6822
Abstract
We will study the formation and processing of dust around carbon- and oxygen-rich evolved stars in the Local Group dwarf galaxy NGC 6822. Dust condensation may depend heavily on the metallicity, although the effect is currently unknown. From current condensation theories it may be expected that: 1) the total condensed dust mass is lower, 2) there will be more simple oxides and less silicates, 3) the degree of crystallinity will be lower for the silicates. We propose to conduct IRS low-resolution observations to study dust properties, such as composition, grain size and shape and the dust mass distribution, to validate current condensation models. We have selected a sample of 20 asymptotic giant branch stars, based on a bandmerge of recent deep near- infrared and extractions from Spitzer SINGS IRAC mid-infrared images of the galaxy. To our knowledge, this will be the first time such evolved stars have been observed spectroscopically in NGC 6822. We will compare the results here to those for stars in the Galaxy and the Magellanic Clouds. Building an understanding of the dust condensation sequence at low metallicities will improve our understanding of dust formation in general, and will provide the ability to use grain properties and dust composition as a tool to trace physical conditions in nearby galaxies.
- Publication:
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Spitzer Proposal
- Pub Date:
- June 2005
- Bibcode:
- 2005sptz.prop20608V