Dust in the SMC: Dust Models from Interstellar Polarization and Extinction Data

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Session 49 -- Interstellar Dust and Polarization
Display presentation, Tuesday, 10, 1995, 9:20am - 6:30pm

[49.02] Dust in the SMC: Dust Models from Interstellar Polarization and Extinction Data

C.V. Rodrigues (U. S\~ao Paulo), G.V. Coyne (Vatican Obs.), A. M. Magalh\~aes (U. S\~ao Paulo)

New polarization and extinction data are used to test various dust models for the Small Magellanic Cloud (SMC). Such data suggest that the monotonic SMC extinction curve is associated with values of the wavelength of maximum polarization ($\lambda_{max}$) which are smaller than the mean value for the Galaxy. However, AZV 456, a star with an extinction similar to the Galactic one, shows also a normal $\lambda_{max}$ value. Dust model fits to the wavelength dependent polarization data are possible for stars with small $\lambda_{max}$. In general, they imply size distributions which are narrower and shifted to smaller sizes as compared to typical Galactic size distributions. However, stars with normal $\lambda_{max}$ which also have a narrower polarization curve, cannot be fit adequately.

The best fits for the extinction curves are obtained with a power law size distribution and assuming that the cylindrical and spherical silicate grains have a size distribution in which the volume distribution from the smaller spheres to the larger cylinders is continuous. The cylindrical population is determined from the fit to the polarization. The 'typical', monotonic SMC extinction curve can be well fit with graphite and silicate grains if a small fraction of the SMC carbon is locked up in the grains. Amorphous carbon and silicate grains also fit the data well. However, AZV 456, with a Galactic extinction curve, has an UV bump which is too blue to be fit by spherical graphite grains.

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