Polarization Simulations of Stellar Wind Bow-shock Nebulae - I. The Case of Electron Scattering
Publication Date
6-11-2018
Document Type
Article
Organizational Units
Physics and Astronomy
Keywords
Polarization, Radiative transfer, Techniques, Polarimetric, Circumstellar matter, Stars, Massive, Stars, Winds, Outflows
Abstract
Bow shocks and related density enhancements produced by the winds of massive stars moving through the interstellar medium provide important information regarding the motions of the stars, the properties of their stellar winds, and the characteristics of the local medium. Since bow-shock nebulae are aspherical structures, light scattering within them produces a net polarization signal even if the region is spatially unresolved. Scattering opacity arising from free electrons and dust leads to a distribution of polarized intensity across the bow-shock structure. That polarization encodes information about the shape, composition, opacity, density, and ionization state of the material within the structure. In this paper, we use the Monte Carlo radiative transfer code SLIP to investigate the polarization created when photons scatter in a bow-shock-shaped region of enhanced density surrounding a stellar source. We present results for electron scattering, and investigate the polarization behaviour as a function of optical depth, temperature, and source of photons for two different cases: pure scattering and scattering with absorption. In both regimes, we consider resolved and unresolved cases. We discuss the implications of these results as well as their possible use along with observational data to constrain the properties of observed bow-shock systems. In different situations and under certain assumptions, our simulations can constrain viewing angle, optical depth and temperature of the scattering region, and the relative luminosities of the star and shock.
Publication Statement
Copyright held by author or publisher. User is responsible for all copyright compliance.
Recommended Citation
Shrestha, Manisha, et al. “Polarization Simulations of Stellar Wind Bow-Shock Nebulae – I. The Case of Electron Scattering.” Monthly Notices of the Royal Astronomical Society, vol. 477, no. 1, 2018, pp. 1365–1382. doi: 10.1093/mnras/sty724.