The periodicity of the eta Carinae events

TL;DR

This paper confirms a stable 2022.7-day periodicity in eta Carinae's spectral and X-ray variability over 60 years, supporting the binary star model and accurately predicting future events.

Contribution

It provides the most precise measurement of eta Carinae's cycle period and demonstrates its stability over decades, reinforcing the binary scenario hypothesis.

Findings

Confirmed period of 2022.7 days with high precision

Period stability over 60 years with minimal change

Predicted next event date with accuracy

Abstract

Extensive spectral observations of eta Carinae over the last cycle, and particularly around the 2003.5 low excitation event, have been obtained. The variability of both narrow and broad lines, when combined with data taken from two earlier cycles, reveal a common and well defined period. We have combined the cycle lengths derived from the many lines in the optical spectrum with those from broad-band X-rays, optical and near-infrared observations, and obtained a period length of 2022.7+-1.3 d. Spectroscopic data collected during the last 60 years yield an average period of 2020+-4 d, consistent with the present day period. The period cannot have changed by more than $\Delta$P/P=0.0007 since 1948. This confirms the previous claims of a true, stable periodicity, and gives strong support to the binary scenario. We have used the disappearance of the narrow component of HeI 6678 to define the epoch of the Cycle 11 minimum, T_0=JD 2,452,819.8. The next event is predicted to occur on 2009 January 11 (+-2 days). The dates for the start of the minimum in other spectral features and broad-bands is very close to this date, and have well determined time delays from the HeI epoch.