A multispectral view of the periodic events in eta Carinae

TL;DR

This paper provides a detailed analysis of the 5.5-year periodic events in Eta Carinae, revealing complex components involving wind interactions and shock collapses, with implications for understanding massive stellar binaries.

Contribution

It introduces a two-component model explaining the periodic events, combining slow wind variations and shock collapse effects, challenging simpler eclipse-based explanations.

Findings

Identification of two distinct components in the cycle: slow variation and collapse.

Anti-correlated radial velocity and intensity changes in spectral lines.

Spectral light curves useful for future event monitoring.

Abstract

A full description of the 5.5-yr low excitation events in Eta Carinae is presented. We show that they are not as simple and brief as previously thought, but a combination of two components. The first, the 'slow variation' component, is revealed by slow changes in the ionization level of circumstellar matter across the whole cycle and is caused by gradual changes in the wind-wind collision shock-cone orientation, angular opening and gaseous content. The second, the 'collapse' component, is restricted to around the minimum, and is due to a temporary global collapse of the wind-wind collision shock. High energy photons (E > 16 eV) from the companion star are strongly shielded, leaving the Weigelt objects at low ionization state for >6 months. High energy phenomena are sensitive only to the 'collapse', low energy only to the 'slow variation' and intermediate energies to both components. Simple eclipses and mechanisms effective only near periastron (e.g., shell ejection or accretion onto the secondary star) cannot account for the whole 5.5-yr cycle. We find anti-correlated changes in the intensity and the radial velocity of P Cygni absorption profiles in FeII 6455 and HeI 7065 lines, indicating that the former is associated to the primary and the latter to the secondary star. We present a set of light curves representative of the whole spectrum, useful for monitoring the next event (2009 January 11).