Simulating the Response of the Secondary Star of Eta Carinae to Mass Accretion at Periastron Passage

Abstract

We use high resolution 3D hydrodynamical simulations to quantify the amount of mass accreted onto the secondary star of the binary system Eta Carinae, exploring two sets of stellar masses that had been proposed for the system, the conventional mass model ($M_1=120 M_{\odot}$ and $M_2=30 M_{\odot}$) and the high mass model ($M_1=170 M_{\odot}$ and $M_2=80 M_{\odot}$). The system consists of two very massive stars in a highly eccentric orbit. Every cycle close to periastron passage the system experiences a spectroscopic event during which many lines change their appearance, accompanied by a decline in x-ray emission associated with the destruction wind collision structure and accretion of the primary wind onto the secondary. We take four different numerical approaches to simulate the response of the secondary wind to accretion. Each affects the mass loss rate of the secondary differently, and in turn determines the amount of accreted mass. The high mass model gives for most approaches much more accreted gas and a longer accretion phase. We find that the effective temperature of the secondary can be significantly reduced due to accretion. We also test different eccentricity values and a higher primary mass loss rate and find their effect on the duration of the spectroscopic event. We conclude that the high mass model is better compatible with the amount of accreted mass, $\approx 3 \times 10^{-6} M_{\odot}$, required for explaining the reduction in secondary ionization photons during the spectroscopic event and compatible with its observed duration.