Journal Article

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

W. J. Tango, J. Davis, A. P. Jacob, A. Mendez, J. R. North, J. W. O'Byrne, E. B. Seneta and P. G. Tuthill

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 396, issue 2, pages 842-848
Published in print June 2009 | ISSN: 0035-8711
Published online June 2009 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2009.14272.x
A new determination of the orbit and masses of the Be binary system δ Scorpii

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The binary star δ 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 M and MB= 8.0 ± 3.6 M. The dynamical parallax is estimated to be 7.03 ± 0.15 mas, which is in good agreement with the revised Hipparcos parallax.

Keywords: techniques: interferometric; binaries: spectroscopic; binaries: visual; stars: fundamental parameters; stars: individual: δ Sco; stars: individual: HR 5953

Journal Article.  4507 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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