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Astron. Astrophys. 324, 1096-1104

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The line-profile variable FORMULA Scorpii is a spectroscopic triple system*

K. De Mey1 and C. Aerts1,**, and C. Waelkens1, and S.R. Cranmer2, and C. Schrijvers3, and J.H. Telting4, and K. Daems1,***, and G. Meeus1

1Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200 B, B-3001 Heverlee, Belgium
2Smithsonian Astrophysical Observatory, 60 Garden Street, MS 50, Cambridge, MA 02138, USA
3Astronomical Institute Anton Pannekoek, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
4Netherlands Foundation for Research in Astronomy, Isaac Newton Group of Telescopes, Apartado 321,
E-38780 Santa Cruz de La Palma, Spain

Received 3 January 1997 / Accepted 4 March 1997


An analysis of 278 spectra of the line-profile variable FORMULA Scorpii leads to the following conclusions.

FORMULA Sco is the primary of a binary system. The radial-velocity variations have a peak-to-peak amplitude of ~ 60 km/s and an orbital period of 5.959 days. The orbit is not circular but has an eccentricity of 0.29. The 5d.959-binary system probably moves in orbit with another distant, as yet unknown third star.

By means of three five-hour time series of high-resolution spectra, the oscillations of the rapidly rotating FORMULA Cephei-type main component are investigated. Line-profile variations, which reveal travelling subfeatures across the lines, are discovered. FORMULA Sco is so far one of the very few FORMULA Cephei stars in which such a moving-bump phenomenon is detected. Radial-velocity variations are derived from the data and analysed to reveal a main oscillation frequency near 4.66 cycles day-1, and some more candidate frequencies. FORMULA Sco is a non-radially pulsating FORMULA Cephei star which rotates supersynchronously.

The characteristics of FORMULA Sco and the FORMULA Oph stars are briefly addressed. Despite the common line-profile behaviour, spectral type, and v sin i, we find no evidence of circumstellar material around FORMULA Sco.

Key words: stars: binaries: spectroscopic - stars: oscillations - stars: individual: FORMULA Scorpii - line: profiles

*Based on observations collected at the European Southern Observatory, La Silla, Chile.
**Postdoctoral Fellow, Fund for Scientific Research, Flanders
***Research Assistant, Fund for Scientific Research, Flanders

© European Southern Observatory (ESO) 1997