Modelling of Sigma Scorpii, a high-mass binary with a Beta Cep variable primary component

TL;DR

This study models the binary system Sigma Scorpii, combining spectroscopic and seismic data to refine stellar parameters and address mass discrepancies in high-mass binaries.

Contribution

It introduces a detailed seismic and spectroscopic analysis of Sigma Scorpii, providing improved mass estimates and insights into pulsation modes of the primary star.

Findings

Primary star mass estimated at 13.5 solar masses after seismic modeling

Secondary star mass refined to approximately 8.7 solar masses

Primary exhibits multiple pulsation modes including radial and non-radial

Abstract

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 Beta 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 solar mass 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 solar mass, and delivers radii of 8.95 +0.43/-0.66 and 3.90 +0.58/-0.36 solar radii for the primary and secondary, respectively. The age of the system is estimated to be ~12 Myr.