SCATTERING OF INFRARED RADIATION BY DUST IN NGC-7023 AND NGC-2023

Linear polarization measurements at 1.25, 1.65, and 2.2 mum of the visual reflection nebulae NGC 7023 and NGC 2023 have been made to determine the contribution of scattered light to the total nebular emission. The percentage polarization of NGC 7023 slowly increases from 0.3 to 1 mum, with peak polarizations of up to 26% at 1.25 mum, then rapidly decreases, with values of 4%-7% at 2.2 mum. We interpret this as implying that scattered starlight contributes most to the short-wavelength emission, while unpolarized emission from small grains or large molecules dominates at longer wavelengths. Infrared polarization and surface brightness measurements are combined to derive the intensity of scattered light, which is then compared with scattering models. While the near-infrared emission of both NGC 2023 and NGC 7023 is dominated by small-grain or large-molecule emission, infrared scattered light plays a larger role in NGC 2023 than in NGC 7023. The near-infrared percentage polarization of NGC 2023 is comparable to the visual percentage polarization, but the polarization position angle appears to rotate with wavelength. The observations are consistent with polarization by scattering of starlight from two distinct sources, HD 37903 and star C, with the position-angle rotation caused by the increasing brightness of star C at longer wavelengths. This picture is supported by previous observations at 0.9 mum showing a small reflection nebula around star C.