Stellar modelling of Spica, a high-mass spectroscopic binary with a beta Cep variable primary component
A. Tkachenko(1), J. M. Matthews(2), C. Aerts(1,3), K. Pavlovski(4), P. I. Papics(1), K. Zwintz(5), C. Cameron(2,6), G. A. H. Walker(2), R. Kuschnig(7), P. Degroote(1), J. Debosscher(1), E. Moravveji(1), V. Kolbas(4), D. B. Guenther(8), A. F. J. Moffat(9), J. F. Rowe(10), S. M. Rucinski(11), D. Sasselov(12), W. W. Weiss(7)
(1) Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium
(2) Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1, Canada
(3) Department of Astrophysics, IMAPP, Radboud University Nijmegen, 6500 GL Nijmegen, The Netherlands
(4) Department of Physics, University of Zagreb, Bijenicka cesta 32, 10000 Zagreb, Croatia
(5) Institute for Astro- and Particle Physics, University of Innsbruck, Technikerstrasse 25/8, Austria
(6) Department of Mathematics, Physics & Geology, Cape Breton University, 1250 Grand Lake Road, Sydney, Nova Scotia, Canada, B1P 6L2
(7) University of Vienna, Institute of Astronomy, Turkenschanzstrasse 17, 1180 Vienna, Austria
(8) Department of Astronomy and Physics, St. Marys University, Halifax, NS B3H 3C3, Canada
(9) Department de physique, Universite de Montreal, C.P.6128, Succ. Centre-Ville, Montreal, QC H3C 3J7, Canada
(10) NASA-Ames Research Park, MS-244-30, Mo ffett Field, CA 94035, USA
(11) Department of Astronomy & Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4, Canada
(12) Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
Binary stars provide a valuable test of stellar structure and evolution, because the masses of the individual stellar components can be derived with high accuracy and in a model-independent way. In this work, we study Spica, an eccentric double-lined spectroscopic binary system with a beta Cep type variable primary component. We use state-of-the-art modelling tools to determine accurate orbital elements of the binary system and atmospheric parameters of both stellar components. We interpret the short-period variability intrinsic to the primary component, detected on top of the orbital motion both in the photometric and spectroscopic data. The non-LTE based spectrum analysis reveals two stars of similar atmospheric chemical composition consistent with the present day cosmic abundance standard defined by Nieva&Przybilla (2012). The masses and radii of the stars are found to be 11.43+/-1.15 M_sun and 7.21+/-0.75 M_sun , and 7.47+/-0.54 R_sun and 3.74+/-0.53 R_sun for the primary and secondary, respectively. We find the primary component to pulsate in three independent modes, of which one is identified as a radial mode, while the two others are found to be non-radial, low degree l modes. The frequency of one of these modes is an exact multiple of the orbital frequency, and the l=m=2 mode identification suggests a tidal nature for this particular mode. We find a very good agreement between the derived dynamical and evolutionary masses for the Spica system to within the observational errors of the measured masses. The age of the system is estimated to be 12.5+/-1 Myr.
Reference: main journal of MNRAS
Status: Manuscript has been accepted
Weblink: http://arxiv.org/abs/1601.08069
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Email: Andrew.Tkachenko@ster.kuleuven.be