Investigating Spatial Distribution of Dust Around SW Vir

Abstract Asymptotic Giant Branch (AGB) stars, which are evolved, low to intermediate mass (1–8MR) 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 dust around AGB stars is critical to our understanding of the contribution of dust to many aspects of astrophysics. In this article we use infrared (IR) spectroscopy to investigate the nature of AGB dust and to test competing hypotheses on dust formation. Here we present recent Gemini/MICHELLE IR observational data of an oxygen-rich AGB star, SW Vir. Using spatially-resolved spectroscopic observations, we determine how the IR spectra change with position in the circumstellar 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 or isotropic, but that it is somewhat axisymmetric. The spatial dependence of the underlying slope in the spectra cannot be attributed to a simple radial dust temperature variation. The apparent radial dependence of the flux intensities is more likely to be due to change in dust density.