A detailed study of the reflection nebula, NGC 7023

Abstract

Polarisation and intensity maps in three broad wavebands are presented for the reflection nebula NGC7023. The data are used to investigate the structure, dust distribution and grain characteristics of the material surrounding the central illuminating star HD200775 of the reflection nebula. Calculations have been made, using a Monte-Carlo technique, for various parameters representing the structure and content of the nebula to predict and explain the observed measurements. The successful description of the observations puts severe restrictions on the nebular parameters. It is found that the geometry of the nebula is in the form of an extended cloud with a foreground conical cavity in which the illuminating star is situated. The dust grains are required to have a power law size distribution of the form n(a) = a(^4.05) and grain material corresponding to silicates is most likely although ice cannot be excluded,