HD161056: A Test of Current Grain Models
Session 14 -- Interstellar Dust and Extinction
Display presentation, Wednesday, January 12, 9:30-6:45, Salons I/II Room (Crystal Gateway)

## [14.07] HD161056: A Test of Current Grain Models

L. He \& D. C. B. Whittet (Rensselaer Polytechnic Institute)

Photometry and polarimetry have been obtained in the line of sight of HD161056 from 0.13 to 4.8 $\mu m$ . The extinction towards HD161056 agrees well with the average extinction,which enables direct comparison between the observed polarization and the predictions of standard grain models. The wavelength dependence of polarization in the UV declines smoothly with decreasing wavelength and is devoid of structure associated with the prominent 2175$\!$\AA \ absorption bump in the interstellar extinction curve. This may suggest that the grains responsible for the bump are not aligned in that line of sight. The polarization predicted by current grain models for standard interstellar extinction are compared with the observations. Greenberg and Duley's models naturally give the best fit to the observation, especially in the UV. Further investigations of the effects of model parameters ( grain shapes, size distribution, alignment, dielctric constants etc.) on the shapes of extinction and polarization curves predicted by current grain models are needed in order to provide more accurate assessment of current grain models.