Polarimetric Variability Hints at Long-term Structural Changes in CV Ser

Abstract Wolf–Rayet binaries that produce carbonaceous dust are important contributors to the Galactic dust budget. The short-period WCd binary CV Serpentis represents an understudied orbital geometry for dust production; it is unclear whether CV Ser’s dust is formed within the circular binary orbit or whether it probes a larger-scale system architecture. We present new polarimetric data on CV Ser, consisting of two data sets spanning the 30 days period but separated by 30 yr. We find that since 1987, both the magnitude and the orientation of the polarization have changed. Because this polarization is caused by light scattering in ionized gas and/or dust in the system, these changes may reflect a long-term variation in its circumstellar structure, such as a long-period wind interaction or the formation of massive dust clumps.