Research Papers (RG)

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Subject: search.filters.subject.Extinction

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    Composite interstellar grains and the 2175˚A feature
    (Organic Matter in Space Proceedings IAU Symposium, 2008-08-14) Vaidya, D.B.; Gupta, Ranjan
    We use discrete dipole approximation (DDA) to study the scattering properties of composite grains made up of host silicate spheroids and graphite inclusions. We calculate the extinction cross sections of the composite grains in the wavelength region 0.20–0.55 μm and study the extinction of the composite grains as a function of graphite inclusions. We present the composite grain model and discuss the results.
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    Composite Interstellar Grains
    (Mon. Not. R. Astron. Soc, 2008-02-01) Vaidya, D.B.; Gupta, Ranjan; Snow, T.P
    A composite dust grain model which is consistent with the observed interstellar extinction and linear polarization is presented. The composite grain is made up of a host silicate spheroid and graphite inclusions. The extinction efficiencies of the composite spheroidal grains for three axial ratios are computed using the discrete dipole approximation (DDA). The interstellar extinction curve is evaluated in the spectral region 3.40–0.10μm using the extinction efficiencies of the composite spheroidal grains. The model extinction curves are then compared with the average observed interstellar extinction curve.We also calculate the linear polarization for the spheroidal composite grains at three orientation angles and find the wavelength of maximum polarization. Further, we estimate the volume extinction factor, an important parameter from the point of view of cosmic abundance, for the composite grain models that reproduce the average observed interstellar extinction. The estimated abundances derived from the composite grain models for both carbon and silicon are found to be lower than that are predicted by the bare silicate/graphite grain models but these values are still higher than that are implied from the recent ISM values.
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    Porous and Fluffy Grains in the Regions of Anomalous Extinction
    (J. Astrophys. Astr., 2000-01-29) Vaidya, D.B.; Anandarao, B. G.; Desai, J.N; et al.
    It has long been established that the ratio of total to selective extinction is anomalously large (³ 5) in certain regions of the interstellar medium. In these regions of anomalous extinction the dust grains are likely to be irregular in shape and fluffy in structure. Using discrete dipole approximation (DDA) we calculate the extinction for porous and fluffy grains. We apply DDA first to solid spheroidal particles assumed to be made of a certain (large) number of dipoles. Then we systematically reduce the number of dipoles to model the porous grains. The aggregates of these particles are suggested to form the fluffy grains. We study the extinction for these particles as a function of grain size, porosity and wavelength. We apply these calculations to interpret the observed extinc tion data in the regions of star formation (e.g. the Orion complex).