Orbital parameters, masses and distance to b Centauri determined with the Sydney University Stellar Interferometer and high-resolution spectroscopy

The bright southern binary star b Centauri (HR 5267) has been observed with the Sydney University Stellar Interferometer (SUSI) and spectroscopically with the European Southern Observatory Coude Auxiliary Telescope and Swiss Euler telescope at La Silla. The interferometric observations have confirmed the binary nature of the primary component and have enabled the determination of the orbital parameters of the system. At the observing wavelength of 442 nm the two components of the primary system have a magnitude difference of 0.15 c 0.02. The combination of interferometric and spectroscopic data gives the following results: orbital period 357.00 c 0.07 d, semimajor axis 25.30 c 0.19 mas, inclination 674 c 03, eccentricity 0.821 c 0.003, distance 102.3 c 1.7 pc, primary and secondary masses M =M= 9.1 c 0.3 M[odot] and absolute visual magnitudes of the primary and secondary MV=-3.85 c 0.05 and MV=-3.70 c 0.05, respectively. The high degree of accuracy of the results offers a fruitful starting point for future asteroseismic modelling of the pulsating binary components.