AbstractsAstronomy & Space Science

ZPEC - The Zodiacal Dust Polarization Evaluation Code:

by E Roebroeks

Institution: Delft University of Technology
Year: 2016
Keywords: zodiacal dust; exozodiacal dust; exoplanets; polarimetry; dust disks; Beta Pictoris; multiple scattering
Posted: 02/05/2017
Record ID: 2073058
Full text PDF: http://resolver.tudelft.nl/uuid:f45b0cc5-4d20-4617-b7d1-be8d280a5a92


The habitability of exoplanets is determined by their surface properties and atmospheres, spectropolarimetry is a powerful tool to characterize these. Numerical models can be used to simulate the polarimetric signals of these exoplanets, but these computed signals have to be compared with observations. The best test-case for such a comparison is the Earth, as the atmospheric and surface properties are well-known and the signal can be computed to a high accuracy. The Lunar Observatory for Unresolved Polarimetry of Earth (LOUPE) shall take measurements of the unresolved Earth being based on the Moon. When observing exoplanets or the Earth, dust in planetary systems acts as a noise source and a source of confusion. This so-called zodiacal dust adds to the polarimetric signal of the planet and in some cases a dust clump might be confused with a planet. The aim of the thesis is to develop a computational tool that allows to analyze the zodiacal dust in order to estimate the noise level and to determine if dust clumps can be distinguished from exoplanets using their polarization signals. The developed computational tool is called ZPEC: the Zodiacal Dust Polarization Evaluation Code. It uses a Monte-Carlo based algorithm in order to track individual photon paths. When photons are scattered their polarization properties are calculated, which are verified using the Adding-Doubling code for flat layers. ZPEC allows to analyze how photon properties change when they are scattered multiple times by a dust particle, whereas classically it is assumed that zodiacal dust disks are optically thin enough to assume photons are scattered only once. The dust model of the COBE/DIRBE mission is used to model the dust in the Solar System, a NASA collisional model was used to model the dust disk surrounding star β Pictoris. The ZPEC photon property databases are used to generate hypothetical detector views. Using ZPEC it is concluded that the Earth sometimes seems to disappear against the polarization signal of the background dust, while the maximum brightness of the dust to the Earth signal is 0.14%. It is also concluded for the dust disk orbiting β Pic that ignoring multiple scattering leads to errors in the calculated polarization signal that are estimated to be 4-9% (relative). In addition it is concluded that dust clumps show the same polarization behavior as the surrounding dust, while planets do not. Hence using brightness only the two can be confused, but they can be distinguished based on their polarization behavior. Advisors/Committee Members: Stam, D.M..