G. Bihain

The substellar mass function in σ Orionis II. Optical, near-infrared and IRAC/Spitzer photometry of young cluster brown dwarfs and planetary-mass objects ,

Aims. We investigate the mass function in the substellar domain down to a few Jupiter masses in the young σ Orionis open cluster (3 ± 2M a,d = 360 +70 −60 pc). Methods. We have performed a deep IJ-band search, covering an area of 790 arcmin 2 close to the cluster centre. This survey was complemented with an infrared follow-up in the HKs- and Spitzer 3.6–8.0 µm-bands. Using colour–magnitude diagrams, we have selected 49 candidate cluster members in the magnitude interval 16.1 mag < I < 23.0 mag. Results. Accounting for flux excesses at 8.0 µm and previously known spectral features of youth, we identify 30 objects as bona fide cluster members. Four are first identified from our optical-near infrared data. Eleven have most probable masses below the deuterium burning limit which we therefore classify as candidate planetary-mass objects. The slope of the substellar mass spectrum – –

Candidate free-floating super-Jupiters in the young

Context. Free-floating substellar candidates with estimated theoretical masses of as low as ~5 Jupiter masses have been found in the ~3 Myr old σ Orionis open cluster. As the overlap with the planetary mass domain increases, the question of how these objects form becomes important. The determination of their number density and whether a mass cut-off limit exists is crucial to understanding their formation. Aims. We propose to search for objects of yet lower masses in the cluster and determine the shape of the mass function at low mass. Methods. Using new- and (re-analysed) published

\sigma

{\it IZJHK}_{\rm s}[3.6]{-}[8.0]

Orionis open cluster

-band data of an area of 840 arcmin 2 , we performed a search for LT-type cluster member candidates in the magnitude range

Near-infrared low-resolution spectroscopy of Pleiades L-type brown dwarfs

J=19.5

Pleiades low-mass brown dwarfs: the cluster L dwarf sequence

–21.5 mag, based on their expected magnitudes and colours. Results. Besides recovering the T type object S Ori 70 and two other known objects, we find three new cluster member candidates, S Ori 72–74, with

The dark nature of GRB 051022 and its host galaxy

J\approx21

Cu and Zn in the early Galaxy

mag and within 12 arcmin of the cluster centre. They have theoretical masses of 4

Search for free-floating planetary-mass objects in the Pleiades

_{-2}^{+3}

Spectroscopic follow-up of L- and T-type proper-motion member candidates in the Pleiades

M Jup and are among the least massive free-floating objects detected by direct imaging outside the Solar System. The photometry in archival Spitzer [3.6]–[5.8]-band images infers that S Ori 72 is an L/T transition candidate and S Ori 73 a T-type candidate, following the expected cluster sequence in the mid-infrared. Finally, the L-type candidate S Ori 74 with lower quality photometry is located at 11.8 arcsec (~4250 AU) of a stellar member of σ Orionis and could be a companion. After contaminant correction in the area complete to