A near-infrared/optical/X-ray survey in the centre of sigma Orionis

Abstract

Because of the intense brightness of the OB-type multiple star system sigma Ori, the low-mass stellar and substellar populations close to the centre of the very young sigma Orionis cluster is poorly know. I present an IJHKs survey in the cluster centre, able to detect from the massive early-type stars down to cluster members below the deuterium burning mass limit. The near-infrared and optical data have been complemented with X-ray imaging. Ten objects have been found for the first time to display high-energy emission. Previously known stars with clear spectroscopic youth indicators and/or X-ray emission define a clear sequence in the I vs. I-Ks diagram. I have found six new candidate cluster members that follow this sequence. One of them, in the magnitude interval of the brown dwarfs in the cluster, displays X-ray emission and a very red J-Ks colour, indicative of a disc. Other three low-mass stars have excesses in the Ks band as well. The frequency of X-ray emitters in the area is 80+/-20 %. The spatial density of stars is very high, of up to 1.6+/-0.1 arcmin-2. There is no indication of lower abundance of substellar objects in the cluster centre. Finally, I also report two cluster stars with X-ray emission located at only 8000-11000 AU to sigma Ori AB, two sources with peculiar colours and an object with X-ray emission and near-infrared magnitudes similar to those of previously-known substellar objects in the cluster.

Accepted for publication in Astron. Nachr. It has not been edited for language yet

References in corpus (3)

• Rotation and accretion of very low mass objects in the SigmaOri cluster
• The brightest stars of the sigma Orionis cluster
• A search for substellar members in the Praesepe and sigma Orionis clusters

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• Dynamical parallax of sigma Ori AB: mass, distance and age
• High-Resolution Chandra X-ray Imaging and Spectroscopy of the Sigma Orionis Cluster
• A deep look into the cores of young clusters I. sigma-Orionis
• A bimodal dust grain distribution in the IC 434 HII region
• A novel survey for young substellar objects with the W-band filter VI: Spectroscopic census of sub-stellar members and the IMF of $\sigma$ Orionis cluster
• Orion revisited III. The Orion Belt population