The brightest stars of the sigma Orionis cluster

Abstract

Context: The very young sigma Orionis cluster (about 3 Ma) is a cornerstone for the understanding of the formation of stars and substellar objects down to planetary masses. However, its stellar population is far to be completely known. Aims: This study has the purpose of identyfing and characterising the most massive stars of sigma Orionis to complement current and future deep searches for brown dwarfs and planetary-mass objects in the cluster. Methods: I have cross-correlated the sources in the Tycho and 2MASS catalogues in a region of 30 arcmin radius with centre in the O-type star sigma Ori A. In the area, I have studied the membership in the Ori OB 1b Association of the brightest stars in the optical using astrometric, X-ray and infrared and optical photometric data from public catalogues and spectroscopic data from the literature. Results: A list of 26 young stars, four candidate young stars and 16 probable foreground stars has arised from the study. Seven young stars probably harbour discs (four are new). There is no mass-dependence of the disc frequency in the cluster. I have derived for the first time the mass spectrum in sigma Orionis from 1.1 to 24 Msol (alpha = +2.0+0.2-0.1; roughly Salpeter-like). I have also provided additional proofs on the existence of several spatially superimposed stellar populations in the direction of sigma Orionis. Finally, the cluster may be closer and older than previously considered.

Accepted by A&A Chief Editor. Sent to language editor. Tables A.1 and A.2 will be only available in electronic form

References in corpus (7)

• Rotation and accretion of very low mass objects in the SigmaOri cluster
• Empirical isochrones and relative ages for young stars, and the radiative-convective gap
• Kinematic structure in the young Sigma Orionis association
• A search for substellar members in the Praesepe and sigma Orionis clusters
• Lithium depleted stars in the young sigma Ori cluster
• Circumstellar discs in the young sigma Orionis cluster
• Are isolated planetary-mass objects really isolated? A brown dwarf-exoplanet system candidate in the sigma Orionis cluster

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• Stars and brown dwarfs in the sigma Orionis cluster: the Mayrit catalogue
• Orbital and physical properties of the $\sigma$ Ori Aa,Ab,B triple system
• Spatial distribution of stars and brown dwarfs in sigma Orionis
• Dynamical parallax of sigma Ori AB: mass, distance and age
• High-Resolution Chandra X-ray Imaging and Spectroscopy of the Sigma Orionis Cluster
• A spectroscopic census in young stellar regions: the Sigma Orionis cluster
• The Villafranca catalog of Galactic OB groups. II. From Gaia DR2 to EDR3 and ten new systems with O stars
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• Low-resolution spectroscopy and spectral energy distributions of selected sources towards sigma Orionis
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• A near-infrared/optical/X-ray survey in the centre of sigma Orionis
• The NEMESIS Catalogue of Young Stellar Objects for the Orion Star Formation Complex. I. General description of data curation
• News from Gaia on sigma Ori E: a case study for the wind magnetic braking process