2012, Authors N-Z

Investigating spatial structure of dust shells around evolved stars

By Angela K. Speck   Mon, Aug 08, 2011

Investigating spatial structure of dust shells around evolved stars

Suklima Guha Niyogi1, Angela K. Speck1 & Kevin Volk2

1University of Missouri
2Space Telescope Science Institute

Abstract:

Cosmic dust is a very important component for any astrophysical environment in which it is found. Asymptotic Giant Branch (AGB) stars, which are evolved, low to intermediate mass (0.8 - 8M; LIMS) stars, are major contributors of material to the interstellar medium (ISM), new stars, planets and also produce the majority of the dust complement of galaxies. AGB stars lose a significant fraction of their mass through slow, massive dust driven winds. Consequently, understanding the dust around AGB stars is crucial to our understanding of the contribution of dust to many aspects of astrophysics. In this article we use infrared spectroscopy method to investigate the nature of AGB dust and to test competing hypotheses on dust formation. We present recent Gemini/MICHELLE infrared (IR) observational data of oxygen-rich AGB star, SW Vir. Using spatially-resolved spectroscopic observations, we determine how the IR spectra and, in particular, specific spectral features associated with individual dust species, change with position around in the circumstellar dust shell. In this way we can discriminate between competing models for the carriers of dust species and for dust formation mechanisms. For SW Vir, the variation in spectral dust features with position show a fairly simple pattern which suggests that the dust shell is not homogenous and isotropic, but that it is somewhat axisymmetric in the distribution of dust features. Furthermore, a prominent and controversial feature at 13 μm is clearly distributed such that it is strongest closest to the central star, although the overall spatial distribution follows the underlying axisymmetry. The location of the 13 μm feature supports the hypothesis that the carrier is crystalline alumina (corundum), a high-temperature and early forming condensate. Furthermore, the distribution of this feature supports the classical dust formation mechanism of seed (oxide) nuclei in a supersaturated gas, followed by (silicate) mantle growth.

By Angela K. Speck