Evolutionary origin of the anomalous fourth star

Explain from stellar-evolution considerations why the three more massive stars in TIC 433545934 have similar properties while the least massive component, star Bb, is substantially cooler and less luminous.

Background

Three components of TIC 433545934 have masses near 2.2–2.4 solar masses and effective temperatures close to 8800 K, whereas the fourth component, Bb, has a much lower mass and temperature and contributes little light. The paper notes that this contrast is not readily explained by the inferred evolutionary state of the system, leaving the origin of the fourth star’s divergent properties unresolved.

References

It is not clear, from an evolutionary point of view, why three of the stars in the system are so similar, while this fourth star, is the odd one out.

— TIC 433545934: The first 2+2 type doubly eclipsing binary with extra, mutual eclipses  (2608.13034 - Borkovits et al., 13 Aug 2026) in Section 6, System parameters