Identify the nature and physical properties of the spectroscopic line-of-sight object

Identify the nature of the additional spectroscopic component $S_{\rm BF}$ detected in the 2020 broadening-function profiles of BS Cas and constrain its physical properties and relationship to the contact-binary system.

Background

The 2020 spectra contain a third broadening-function peak that is absent from the 2018 spectra. The component has a nearly constant radial velocity and a light contribution consistent with some of the modeled third-light values, but its radial-velocity behavior is inconsistent with the predicted motion of the LTT companion. The authors therefore interpret SBFS_{\rm BF} as likely unbound and projected along the same line of sight, while explicitly acknowledging that its identity and physical properties remain unresolved.

References

At present, however, the available observational material does not allow a definitive identification of the nature of $S_{\rm BF}$, nor does it permit stringent constraints on its physical properties.

— BS Cassiopeiae: A Contact Binary with Starspot-Driven Variability and Evidence for Additional Components  (2609.30792 - Jeong et al., 25 Sep 2026) in Section 6, Summary and Conclusions