AAS 207th Meeting, 8-12 January 2006
Session 119 The Dirty Side of the ISM - Theory and Dust
Poster, Wednesday, 9:20am-6:30pm, January 11, 2006, Exhibit Hall

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[119.10] Observational Constraints on Interstellar Grain Alignment

B-G Andersson (JHU), S.B. Potter (SAAO)

We present new multi-band polarimetry of stars probing the dust in the Southern Coalsack. Complementing our observations with archival photometric and polarimetric data, of both the Coalsack and other nearby clouds, we find that the wavelength of maximum polarization (\lambdamax) is tightly correlated with the amount of extinction seen by the grains - though not necessarily with the line-of-sight visual extinction. \lambdamax is not as well correlated with the ratio of total to selective extinction (RV) in the individual clouds. However, an offset in the zero-intercept between different clouds is detected which does correlate with the average values of RV. These \lambdamax vs. AV correlation supports recent theoretical predictions that the grain alignment is driven by radiative processes. The offsets in \lambdamax zero-intercepts likely reflect variations in the total grain size distributions between the clouds.

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