B, V and R band polarimetry of DH Cep

Lomb-Scargle period search has been applied to the acquired polarization data to reveal the dominating frequency in polarization variations. We also used a standard analytical method based on a two-harmonics Fourier fit to derive the inclination, orientation, and the direction of rotation of the binary orbit. The variations of Stokes parameters in all three B, V, and R passbands clearly exhibit an unambiguous periodic signal at 1.055d with the amplitude of variations ~0.2% which corresponds to half of the known orbital period of 2.11d.

This type of polarization variability is expected for a binary system with light scattering material distributed symmetrically with respect to the orbital plane. In addition to the regular polarization variability, there is a non-periodic component, strongest in the B passband. We obtained in the V passband our most reliable values for the orbital inclination i=46{deg}+11{deg}/-46{deg} and the orientation of the orbit on the sky {Omega}=105{deg}+/-55{deg}, with 1{sigma} confidence intervals.

Using our best estimate of i and the polarimetric amplitude in the V passband, we estimated that the mass-loss of the system is ~3.4x10^-7^M_{sun}_/yr. The direction of the binary system rotation on the plane of the sky is clockwise. Our polarimetric observations of neighboring stars of DH Cep in NGC 7380 reveal that the polarization of the cluster stars is most likely due to aligned interstellar dust in the foreground.