Ranjan Gupta, Pune, India ()
"Interstellar Extinction and Modeling of Dust"
Abstract. It is well known that interstellar dust plays the most important role in which the light seen from stars suffers extinction. Conventional models assume Mie theory of light scattering with solid spheres and other shapes of silicate and graphite particles of different sizes. An extension of this theory was Effective Medium Theory (EMT) which tries to explain some of the observed interstellar properties.Recent space probes have confirmed that the dust grains are highly porous and fluffy (i.e. aggregates or clusters) rather than having regularshapes (spherical,cylindrical or spheroidal) and homogeneous in composition and structure. Since there is no exact theory for calculation of scatteringproperties of such irregular, inhomogeneous particles, recently our group has used Discrete dipole approximation (DDA) method and the results of thisinvestigation will be discussed. The model uses a composite fluffy dust grain for explaining most of the observed interstellar extinction curvesand also polarization. Another parameter which needs to be constrained by the dust models is the interstellar abundances of Carbon andSilicon which is usually overestimated by the solid dust models but our model predicts closer match to the observed ISM abundances.The Silicate dust emission features at 10 and 18 microns is also explained by our composite grain model which helps in understandingthe dust characteristics in the circumstellar dust shells around the stars.
Held in the AAO Conference room at 03:30 PM on Monday, 08 March 2010back