ITAL]HUBBLE SPACE TELESCOPE[/ITAL][ITAL]Hubble Space Telescope[/ITAL] Imaging Polarimetry of η Carinae

Abstract

Linear polarization measurements have been a key to our understanding of the massive star system ? Carinae and its surrounding Homunculus nebula. We here present the results of (linear) polarimetric imaging of ? Carinae in the V band (F555W) with the Hubble Space Telescope's Wide Field Planetary Camera 2 (HST/WFPC2). The data agree well with previous ground-based measurements of the large-scale polarization across the Homunculus, allowing us to confirm that it is primarily a reflection nebula. The HST observations add information on the variation of the polarization across the lobes on small spatial scales. We provide measurements of the polarization in a variety of structures such as the jet, the skirt, the paddle, the southern ridge, and the spot, and discuss the properties of the polarization of the Homunculus on large and small spatial scales. Using a simple Mie-scattering model, we argue that of three previously proposed geometries for the three-dimensional structure of the Homunculus only the double-flask geometry represents a dust distribution which is consistent with our polarization map.