On the Formation of SS433

SS433 is an extraordinary X-ray binary that is ejecting bipolar jets at 26% the speed of light. Associated with the supernova-like shell W50, SS433 is also probably one of the youngest X-ray binaries with an age of less than or similar to 10(5)yr. However, the masses of the two components in SS433 and even the nature of the compact object are still under debate. In this work, assuming that the compact object is a black hole, we employ a binary population synthesis method to study the formation of SS433. We use previous estimates of the age of W50 and the duration of the jet activity to constrain the evolutionary history. Our calculations suggest that SS433 likely harbored a Hertzsprung gap star at the beginning of the current Roche-lobe overflow phase. The masses of the black hole and the optical/donor star in SS433 suggested by the simulations are around 8M(circle dot;)and 24M(circle dot;), respectively. Future measurement of the donor mass and radius can help infer not only the origin of the binary but also the nature of the nebula W50.