A multispectral view of the periodic events in eta Carinae

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).

arXiv comment16 pages, 7 EPS figures, accepted for publication on MNRAS

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