Interpretation of photo-polarimetric observations of comet 17P/Holmes

摘要

We present multispectral photo-polarimetric observations of comet 17P/Holmes taken at three different dates. These observations show the evolution of the negative polarization branch (NPB) as a function of time and wavelength. We perform discrete-dipole approximation (DDA) simulations on agglomerated debris particles of various sizes and refractive indices. Our simulations show that the observations are consistent with the cloud being composed of agglomerated debris particles having refractive indices of approximately m=1.5-1.6+0.1i. Our results are also consistent with the particles obeying a power-law size distribution r~(-a) and having a lower particle-radius cut-off of approximately 0.6γm, where the index a~3.5 for the early observations and shrinks to a~1.5 for the later observations. This is consistent with the smaller, more accelerated particles in the distribution being propelled out of the field of view.