The 2011 Periastron Passage of the Be Binary delta Scorpii

A. S. Miroshnichenko1, A. V. Pasechnik2, N. Manset3, A. C. Carciofi4, Th. Rivinius5, S. Štefl6, V. V. Gvaramadze7,8, J. Ribeiro9, A. Fernando10, T. Garrel11, J. H. Knapen12,13, C. Buil14, B. Heathcote15, E. Pollmann16, B. Mauclaire17, O. Thizy18, J .Martin19, S. V. Zharikov20, A. T. Okazaki21, T. L. Gandet22, T. Eversberg23, and N. Reinecke24

1 Department of Physics and Astronomy, University of North Carolina at Greensboro, Greensboro, NC 27402-6170, USA
2 Tuorla Observatory, Department of Physics and Astronomy, University of Turku, Finland
3 CFHT Corporation, 65-1238 Mamalahoa Hwy, Kamuela, HI 96743
4 Instituto de Astronomia, Geofísica e Ciéncias Atmosféricas, Universidade de São Paulo, Brazil
5 ESO - European Organisation for Astronomical Research in the Southern Hemisphere, Casilla 19001, Santiago 19, Chile
6 ESO/ALMA, Alonso de Córdova 3107, Vitacura, Santiago, Chile
7 Sternberg Astronomical Institute, Lomonosov Moscow State University, Universitetskij Pr. 13, Moscow 119992, Russia
8 Isaac Newton Institute of Chile, Moscow Branch, Universitetskij Pr. 13, Moscow 119992, Russia
9 Observatorio do Instituto Geografico do Exercito, Lisboa, Portugal
10 ATALAIA.org Group-Lisboa, Portugal
11 Observatoire de Juvignac, 19 avenue du Hameau du Golf 34990, Juvignac, France
12 Instituto de Astrofísica de Canarias, E38205 La Laguna, Tenerife, Spain
13 Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Spain
14 Castanet Tolosan Observatory, 6 place Clémence Isaure 31320 Castanet Tolosan, France
15 Barfold Observatory, Glenhope, Victoria 3444, Australia
16 Emil-Nolde-Str. 12, 51375, Leverkusen, Germany
17 Observatoire du Val de l'Arc, route de Peynier 13530 Trets, France
18 Shelyak Instruments, 1116 route de Chambery, F-38330 Saint-Ismier, France
19 Barber Research Observatory, Department of Physics and Astronomy, University of Illinois-Springfield, IL 62703, USA
20 Instituto de Astronomia, Universidad Nacional Autónoma de Mexico, Apdo. Postal 877, Ensenada, 22800, Baja California, Mexico
21 Faculty of Engineering, Hokkai-Gakuen University, Toyohira-ku, Sapporo 062--8605, Japan
22 Lizard Hollow Observatory, P.O. Box 89175, Tucson, AZ 85752-9175, USA
23 Schnörringen Telescope Science Institute, Waldbröl, Germany
24 Fontainegraben 150, 53123, Bonn, Germany

We describe the results of the world-wide observing campaign of the highly eccentric Be binary system delta Scorpii 2011 periastron passage which involved professional and amateur astronomers. Our spectroscopic observations provided a precise measurement of the system orbital period at 10.8092+-0.0005 years. Fitting of the HeII 4686 Angstrom line radial velocity curve determined the periastron passage time on 2011 July 3, UT 9:20 with a 0.9-day uncertainty. Both these results are in a very good agreement with recent findings from interferometry. We also derived new evolutionary masses of the binary components (13 and 8.2 Msun) and a new distance of 136 pc from the Sun, consistent with the HIPPARCOS parallax. The radial velocity and profile variations observed in the Halpha line near the 2011 periastron reflected the interaction of the secondary component and the circumstellar disk around the primary component. Using these data, we estimated a disk radius of 150 Rsun. Our analysis of the radial velocity variations measured during the periastron passage time in 2000 and 2011 along with those measured during the 20th century, the high eccentricity of the system, and the presence of a bow shock-like structure around it suggest that delta Sco might be a runaway triple system. The third component should be external to the known binary and move on an elliptical orbit that is tilted by at least 40 degree with respect to the binary orbital plane for such a system to be stable and responsible for the observed long-term radial velocity variations.

Accepted by The Astrophysical Journal
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or on the web at: arXiv:1302.4021

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