Accretion onto the Companion of Eta Carinae

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Amit Kashi worked on his PhD under the supervision of Prof. Noam Soker. The title of his thesis is "The Periastron Passage of the Binary star Eta Carinae".

Amit is fascinated by this star and the variety of physical processes that  take place in the binary system, and studied this system from almost every possible aspect. Amit is presently working on a few more subjects: Transient events (strange astrophysical explosions with energy between Nova and Supernova, which cannot be explained by simple processes), mass transfer in binaries, and formation of planets, brown dwarfs and stars around very massive stars of 100 solar mass or more.

 Accretion onto the Companion of Eta Carinae:

Eta Carinae is a unique massive binary star system in our Galaxy, presenting some basic undetermined parameters and open questions. Its 5.54 year periodicity in a very eccentric orbit is observed in all wavelengths. We identify the important physical processes that we expect to take place at periastron passage, and use these to explain observations.

We show that close to periastron mass accretion onto the companion is expected to occur. The accreted mass possesses enough angular momentum to form a thick belt around the secondary, and shuts down the secondary wind for ten weeks. This explains the minimum in the X-ray luminosity and in other bands, known as the spectroscopic event. After periastron the belt dissipates as its mass is being blown away by the reestablished secondary wind, and the system recovers from the spectroscopic event.

Our study emphasizes that mass transfer is an important process in the evolution of close massive binaries. The high luminosity and ejected mass of many eruptive events can be explained by mass transfer, e.g., the twenty-years long Great Eruption of Eta Carinae and some intermediate luminosity optical transients

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