Accretion onto the Companion of η Carinae during the Spectroscopic Event. III. The Heiiλ4686 Line

Abstract

We continue to explore the accretion model of the massive binary system η Car by studying the anomalously high He II λ4686 line. The line appears just before periastron and disappears immediately thereafter. Based on the He II λ4686 line emission from O stars and their modeling in the literature, we postulate that the He II λ4686 line comes from the acceleration zone of the secondary stellar wind. We attribute the large increase in the line intensity to a slight increase in the density of the secondary stellar wind in its acceleration zone. The increase in density could be due to the ionization and subsequent deceleration of the wind by the enhanced X-ray emission arising from the shocked secondary wind farther downstream or to accretion of the primary stellar wind. Accretion around the secondary equatorial plane gives rise to collimation of the secondary wind, which increases its density, hence enhancing the He II λ4686 emission line. In contrast with previous explanations, the model proposed in this paper does not require a prohibitively high X-ray flux to directly photoionize the He.