The Environments around W Serpentis Systems: Independent Limits on System Masses and Extended Envelopes

Abstract

Information extracted from the Gaia Data Release 3 is used to examine the stellar contents within projected separations of 10 pc from eight close binary systems that are either classical W Serpentis systems or related objects. The goal is to search for remnant star clusters or moving groups with proper motions that are similar to those of the binaries. While some of the binary systems have proper motions that are distinct from those of the majority of stars within the search area, there is a tendency for W Ser stars to be accompanied by companions with separations on parsec or larger scales. At least three candidate companions are identified within the search area for each system, although in the majority of cases the numbers are much higher. Evidence is presented that SX Cas is near the center of a diffuse cluster. Color–magnitude diagrams of the groupings associated with the binaries are compared with isochrones, and the majority of the groupings are found to have ages ≥1 Gyr, indicating that they have an intermediate age. The masses of stars at the main-sequence turnoff of the groupings are estimated, and these provide insights into the initial mass of the donor star in each binary system. Images from the WISE All-Sky Survey are also used to search for circumsystem envelopes. Extended thermal emission is found around six systems in W2 (i.e., ∼4.5 μm) images.