Impact of hot exozodiacal dust on the polarimetric analysis of close-in exoplanets

Interferometric near- and mid-infrared observations revealed that about one-fifth of nearby stars are surrounded by dust of as yet unknown origin - hot exozodiacal dust (HEZD). Since HEZD is located  at orbital radii comparable to those of close-in exoplanets, its presence has a potential influence on the analysis of the scattered-light polarization of close-in exoplanets and vice versa.

We analyze the impact of HEZD around main-sequence stars on the polarimetric characterization of close-in exoplanets and vice versa by identifying characteristic polarimetric signatures of HEZD and close-in exoplanet. We find that the dust grain radius has the strongest influence on a polarimetric analysis due to its significant impact on the wavelength-dependent polarization characteristics and the total order of magnitude of the scattered-light polarization. In certain scenarios, the scattered-light polarization of the HEZD even exceeds that of the close-in exoplanet, for example for a dust grain radius of 0.1 μm, a HEZD mass of 8*10^-10 Μ_⊕ , an orbital HEZD radius of 0.04 au and an orbital inclination of 90°.
 
In summary, the presence of HEZD needs to be considered in any effort to characterize exoplanets via polarimetric observations. Stricter constraints on the model parameters (especially on the dust grain radii) are required to restrict the potentially resulting scattered-light polarization.