The Complex Circumstellar and Circumbinary Environment of V356 Sgr

TL;DR

This study uses 21 years of spectropolarimetric data to investigate the complex circumstellar environment of V356 Sgr, revealing a large intrinsic polarization and variable scattering structures, indicating dynamic mass transfer processes.

Contribution

It provides the first detailed characterization of the circumstellar geometry of V356 Sgr, identifying a possible circumbinary disk or bipolar outflows and observing variability in scattering material.

Findings

Detection of large intrinsic polarization from electron scattering.

Identification of non-occulted scatterers suggesting a circumbinary structure.

Observation of cycle-to-cycle polarization variability indicating changing scattering material.

Abstract

We analyze 45 spectropolarimetric observations of the eclipsing, interacting binary star V356 Sgr, obtained over a period of 21 years, to characterize the geometry of the system's circumstellar material. After removing interstellar polarization from these data, we find the system exhibits a large intrinsic polarization signature arising from electron scattering. In addition, the lack of repeatable eclipses in the polarization phase curves indicates the presence of a substantial pool of scatterers not occulted by either star. We suggest that these scatterers form either a circumbinary disk coplanar with the gainer's accretion disk or an elongated structure perpendicular to the orbital plane of V356 Sgr, possibly formed by bipolar outflows. We also observe small-scale, cycle-to-cycle variations in the magnitude of intrinsic polarization at individual phases, which we interpret as evidence of variability in the amount of scattering material present within and around the system. This may indicate a mass transfer or mass loss rate that varies on the time-scale of the system's orbital period. Finally, we compare the basic polarimetric properties of V356 Sgr with those of the well studied beta Lyr system; the significant differences observed between the two systems suggests diversity in the basic circumstellar geometry of Roche-lobe overflow systems