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 \gtrsim 2 \pm 1 mas formed around the primary in 2000 .
By 2006/2007 the size of this region grew to an estimated \gtrsim 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 M _ { A } = 15 \pm 7 M _ { \odot } and M _ { B } = 8.0 \pm 3.6 M _ { \odot } .
The dynamical parallax is estimated to be 7.03 \pm 0.15 mas , which is in good agreement with the revised HIPPARCOS parallax .