A new determination of the orbit and masses of the Be binary system delta Scorpii

TL;DR

This paper refines the orbit and mass estimates of the Be binary star delta Scorpii using interferometric and spectroscopic data, revealing changes in the emission region size around the primary star over time.

Contribution

It provides a new, consistent set of orbital elements and mass estimates for delta Scorpii, incorporating recent interferometric observations and modeling the emission region growth.

Findings

Mass of primary: 15 +/- 7 solar masses

Mass of secondary: 8.0 +/- 3.6 solar masses

Dynamical parallax: 7.03 +/- 0.15 mas

Abstract

The binary star delta Sco (HD143275) underwent remarkable brightening in the visible in 2000, and continues to be irregularly variable. The system was observed with the Sydney University Stellar Interferometer (SUSI) in 1999, 2000, 2001, 2006 and 2007. The 1999 observations were consistent with predictions based on the previously published orbital elements. The subsequent observations can only be explained by assuming that an optically bright emission region with an angular size of > 2 +/- 1 mas formed around the primary in 2000. By 2006/2007 the size of this region grew to an estimated > 4 mas. We have determined a consistent set of orbital elements by simultaneously fitting all the published interferometric and spectroscopic data as well as the SUSI data reported here. The resulting elements and the brightness ratio for the system measured prior to the outburst in 2000 have been used to estimate the masses of the components. We find Ma = 15 +/- 7 Msun and Mb = 8.0 +/- 3.6 Msun. The dynamical parallax is estimated to be 7.03 +/- 0.15 mas, which is in good agreement with the revised HIPPARCOS parallax.