This dissertation presents a comprehensive study of multi-wavelength optical po¬larimetry applied to stellar systems exhibiting variable intrinsic polarization, with a focus on close binary stars and exoplanets. Using high-precision broadband po¬larimetry with the DiPol-2 instrument on the remotely controlled T60 telescope, we have measured polarization variations with the phase of the orbital period in three O+O binary systems (AO Cassiopeiae (AO Cas), DH Cephei (DH Cep), and HD 165052) and the exoplanet Upsilon Andromedae b ( And b). For two binary sys¬tems, DH Cep and HD 165052, phase-locked small-amplitude polarization variabil¬ity has been detected and analyzed for the very frst time.

For the binary systems, we derived orbital parameters through Fourier analy¬sis of polarization variability, obtaining inclinations and orientations of the orbital planes. Our analysis revealed symmetric distributions of scattering material consis¬tent with Thomson scattering in circumstellar environments. We estimated interstel¬lar polarization contributions through observations of feld stars, revealing uniform dust distributions in the young open stellar cluster NGC 7380 (DH Cep), but strong non-uniformity in cluster NGC 6530 (HD 165052).

For the exoplanet And b, we detected weak periodic signals at half the or¬bital period but faced challenges in orbital and physical parameters extraction due to very small amplitude of periodic variations and low signal-to-noise. Our Rayleigh-Lambert modeling yielded tentative estimates of planetary orbital parameters and ge¬ometric albedo but with large uncertainties, demonstrating diffculties in exoplanet polarimetry which requires accuracy much better than 10−5.

This work demonstrates polarimetry’s unique ability to probe orbital geometries and scattering environments in stellar systems, while establishing the current limi¬tations for exoplanet characterization. The research advances our understanding of binary star dynamics and circumstellar environments while outlining pathways for future high-sensitivity polarimetric studies.