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

Cited by in corpus (13)

• Fitting the young main-sequence; distances, ages and age spreads
• FLAMES spectroscopy of low-mass stars in the young clusters sigma Ori and lambda Ori
• Adaptive Optics Photometry and Astrometry of Binary Stars. III. A Faint Companion Search of O-Star Systems
• Main-Seqence Fitting Distance to the sigma Ori Cluster
• Stars and brown dwarfs in the sigma Orionis cluster: the Mayrit catalogue
• 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
• Accretion properties of T Tauri stars in sigma Ori
• Young stars and brown dwarfs surrounding Alnilam (eps Ori) and Mintaka (del Ori)
• Low-resolution spectroscopy and spectral energy distributions of selected sources towards sigma Orionis
• New deep XMM-Newton observations to the west of the sigma Orionis cluster
• A near-infrared/optical/X-ray survey in the centre of sigma Orionis