Evolutionary status of ZZ PsA

Establish the evolutionary status of the contact binary ZZ PsA through further long-term photometric and spectroscopic monitoring, specifically determining whether it is dynamically unstable and close to coalescence or remains a borderline, stable configuration.

Background

ZZ PsA has an extremely low mass ratio and a very high fill-out factor, making it a potential merger candidate. Its spin-to-orbital angular-momentum ratio lies slightly below the classical Darwin-instability threshold, but the uncertainty interval extends above that threshold. Its observed mass ratio is likewise close to the instability value, and different instability criteria yield non-identical classifications.

Because the available measurements do not distinguish decisively between stability and instability, the authors characterize ZZ PsA as a borderline rather than unambiguous merger candidate and call for long-term observations.

References

The evolutionary status of ZZ PsA remains uncertain and requires further long-term photometric and spectroscopic monitoring.

— CoBiToM project. III. Physical characterisation of the potential merger candidates AL Lep, ASAS J082243+1927.0, and ZZ PsA  (2608.28051 - Palafouta et al., 28 Aug 2026) in Section 7, Discussion

These objects show that the low mass ratio limit remains an open problem requiring both larger observational samples and refined stability calculations.

— Extremely Low Mass Ratio Contact Binaries. III. Photometric and Spectroscopic Investigations of Eleven Systems  (2608.28066 - Lai et al., 28 Aug 2026) in Section 1, Introduction