A deep look into the cores of young clusters I. sigma-Orionis

Abstract

Nearby young clusters are privileged places to study the star formation history. Over the last decade, the sigma-Orionis cluster has been a prime location for the study of young very low mass stars, substellar and isolated planetary mass objects and the determination of the initial mass function. To extend previous studies of this association to its core, we searched for ultracool members and new multiple systems within the 1.5'x1.5' central region of the cluster. We obtained deep multi-conjugate adaptive optics (MCAO) images of the core of the sigma-Orionis cluster with the prototype MCAO facility MAD at the VLT using the H and Ks filters. These images allow us to reach Delta H~5mag as close as 0.2" on a typical source with H=14.5mag. These images were complemented by archival SofI Ks-band images and Spitzer IRAC and MIPS mid-infrared images. We report the detection of 2 new visual multiple systems, one being a candidate binary proplyd and the other one a low mass companion to the massive star sigma Ori E. Of the 36 sources detected in the images, 25 have a H-band luminosity lower than the expected planetary mass limit for members, and H-Ks color consistent with the latest theoretical isochrones. Nine objects have additional Spitzer photometry and spectral energy distribution consistent with them being cluster members. One of them has a spectral energy distribution from H to 3.6micron consistent with that of a 5.5 MJup cluster member. Complementary NTT/SofI and Spitzer photometry allow us to confirm the nature and membership of two L-dwarf planetary mass candidates.

Accepted for publication in A&A 16 pages, 8 tables, 10 figures

References in corpus (15)

• Spitzer/IRAC Photometry of M, L, and T Dwarfs
• Rotation and accretion of very low mass objects in the SigmaOri cluster
• Fitting the young main-sequence; distances, ages and age spreads
• Kinematic structure in the young Sigma Orionis association
• Main-Seqence Fitting Distance to the sigma Ori Cluster
• Contamination by field late-M, L and T dwarfs in deep surveys
• 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
• A search for substellar members in the Praesepe and sigma Orionis clusters
• New constraints on the membership of the T dwarf S Ori 70 in the sigma Orionis cluster
• Accretion properties of T Tauri stars in sigma Ori
• Lithium depleted stars in the young sigma Ori cluster
• Multi-Conjugate Adaptive Optics images of the Trapezium Cluster
• A near-infrared/optical/X-ray survey in the centre of sigma Orionis

Cited by in corpus (13)

• A rich population of free-floating planets in the Upper Scorpius young stellar association
• Substellar Objects in Nearby Young Clusters (SONYC): The bottom of the Initial Mass Function in NGC1333
• B fields in OB stars (BOB): Concluding the FORS2 observing campaign
• Orbital and physical properties of the $\sigma$ Ori Aa,Ab,B triple system
• The Gould's Belt Very Large Array Survey III. The Orion region
• Low-resolution spectroscopy and spectral energy distributions of selected sources towards sigma Orionis
• The origin of free-floating planets
• New deep XMM-Newton observations to the west of the sigma Orionis cluster
• A search for pre- and proto-brown dwarfs in the dark cloud Barnard 30 with ALMA
• Stellar photometry with Multi Conjugate Adaptive Optics
• Ultra-Wideband, Multi-epoch Radio Study of the First Discovered `Main sequence Radio Pulse emitter' CU Vir
• From 1000 AU to 1000 pc: high proper-motion stars in the solar neighbourhood, radio sources in the sigma Orionis cluster, and new X-ray stars surrounding Alnilam
• Disk fraction among free-floating planetary-mass objects in Upper Scorpius