A third massive star component in the \sigma\ Orionis AB system

TL;DR

This study reveals a third massive star in the ija Orionis AB system, changing it from a binary to a triple system through spectroscopic and astrometric analysis.

Contribution

It provides the first spectroscopic evidence of a third star in the ija Orionis AB system and determines its orbital parameters.

Findings

Detected a third massive star component.

Determined the orbital period as approximately 143.5 days.

Confirmed the system is a triple star system.

Abstract

We report on the detection of a third massive star component in the \sigma\ 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 \sigma\ Orionis AB system when combined with previous results obtained from the study of the astrometric orbit (with an estimated period of ~157 yr).