Nature of Eta Carinae’s pre-periastron photometric peak

Determine the physical nature of Eta Carinae’s recurring pre-periastron photometric peak, including whether it results from maximum Roche-lobe overfilling of the primary star, mass flow toward the secondary, an ejection event, a post-periastron eclipse of transferred material, or a combination of these processes.

Background

The paper identifies a sharp, recurring photometric peak before periastron in Eta Carinae’s orbital light curve. The peak occurs at a consistent orbital phase, its amplitude decreases from approximately 0.45 magnitudes in 2003.4 and 2009.1 to approximately 0.3 magnitudes in 2020.2 and 2025.7, and the stellar-core B−V color remains roughly constant. These properties indicate that the phenomenon is associated with additional material reflecting or obscuring the primary star’s light rather than with ordinary ellipsoidal deformation alone.

Several possible physical interpretations are discussed but not resolved. The peak may correspond to the primary star’s largest Roche-lobe overfilling near periastron, to gas flowing toward the secondary, to a sudden ejection, or to the leading edge of an eclipse involving post-periastron transferred material. Resolving its nature is important for testing the proposed scenario of periodic Roche-lobe overflow and episodic mass transfer in the highly eccentric Eta Carinae binary.

References

This requires a quantitative demonstration, as it is not clear how this material stays close enough to the primary.

— The 2025.6 X-ray Minimum of Eta Carinae  (2609.20046 - Kashi et al., 17 Sep 2026) in Section 3, Results

The nature of this peak is uncertain. It may be when the primary star has reached its largest Roche lobe overfilling near periastron. Note that it always occurs at the same orbital phase, and the B-V color index of the stellar core remained roughly constant. The flow of gasses towards the secondary was also suggested by \citet{soker01} and \citet{kashi19}.

— Eta Carinae's historical light curve: evidence for cyclic Roche lobe overflow from the primary star  (2608.16818 - Damineli et al., 17 Aug 2026) in Section 3.5, “The pre-periastron photometric peak” (Section label: peak)