A third massive star component in the σ Orionis AB system

Abstract

We report on the detection of a third massive star component in the σ Orionis AB system, traditionally considered as a binary system. The system has been monitored by the IACOB spectroscopic survey of Northern Massive stars program, obtaining 23 high-resolution FIES@NOT spectra with a time-span of ~2.5 years. The analysis of the radial velocity curves of the two spectroscopic components observed in the spectra has allowed us obtain the orbital parameters of the system, resulting in a high eccentric orbit (e~0.78) with an orbital period of 143.5 +/- 0.5 d. This result implies the actual presence of three stars in the σ Orionis AB system when combined with previous results obtained from the study of the astrometric orbit (with an estimated period of ~157 yr).

7 pages, 3 figures, 2 tables. Accpeted for publication in ApJ

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