Modelling of σ Scorpii, a high-mass binary with a β Cep variable primary component

• Published in: Monthly notices of the Royal Astronomical Society Vol. 442; no. 1; pp. 616 - 628
• Main Authors: Tkachenko, A., Aerts, C., Pavlovski, K., Degroote, P., Pápics, P. I., Moravveji, E., Lehmann, H., Kolbas, V., Clémer, K.
• Format: Journal Article
• Language: English
• Published: Oxford University Press 21-07-2014
• Subjects: stars: fundamental parameters; stars: oscillations; binaries: spectroscopic; stars: individual: σ Scorpii; stars: variables: general
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stu885

High-mass binary stars are known to show an unexplained discrepancy between the dynamical masses of the individual components and those predicted by models. In this work, we study Sigma Scorpii, a double-lined spectroscopic binary system consisting of two B-type stars residing in an eccentric orbit. The more massive primary component is a β Cep-type pulsating variable star. Our analysis is based on a time series of some 1000 high-resolution spectra collected with the CORALIE spectrograph in 2006, 2007, and 2008. We use two different approaches to determine the orbital parameters of the star; the spectral disentangling technique is used to separate the spectral contributions of the individual components in the composite spectra. The non-LTE-based spectrum analysis of the disentangled spectra reveals two stars of similar spectral type and atmospheric chemical composition. Combined with the orbital inclination angle estimate found in the literature, our orbital elements allow a mass estimate of 14.7 ± 4.5 and 9.5 ± 2.9 M⊙ for the primary and secondary component, respectively. The primary component is found to pulsate in three independent modes, of which two are identified as fundamental and second overtone radial modes, while the third is an l = 1 non-radial mode. Seismic modelling of the pulsating component refines stellar parameters to 13.5
$^{+0.5}_{-1.4}$
and 8.7
$^{+0.6}_{-1.2}$
M⊙, and delivers radii of 8.95
$^{+0.43}_{-0.66}$
and 3.90
$^{+0.58}_{-0.36}$
R⊙ for the primary and secondary, respectively. The age of the system is estimated to be ∼12 Myr.