The substellar mass function in sigma Orionis II. Optical, near-infrared and IRAC/Spitzer photometry of young cluster brown dwarfs and planetary-mass objects
Abbreviated Journal Title
stars : low mass, brown dwarfs; Galaxy : open clusters and associations; : individual : sigma Orionis; stars : planetary systems : protoplanetary; discs; EXTRASOLAR GIANT PLANETS; COLOR-MAGNITUDE DIAGRAMS; EVOLUTIONARY MODELS; NEBULA CLUSTER; GALACTIC STRUCTURE; ULTRACOOL DWARFS; IMAGING-SURVEY; MAIN-SEQUENCE; COOL DWARFS; GAS CLOUDS; Astronomy & Astrophysics
Aims. We investigate the mass function in the substellar domain down to a few Jupiter masses in the young sigma Orionis open cluster ( 3 +/- 2Ma, d = 360(-60)(+70)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 mu m-bands. Using colour-magnitude diagrams, we have selected 49 candidate cluster members in the magnitude interval 16.1 mag < I < 23.0mag. Results. Accounting for flux excesses at 8.0 mu m 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 (Delta N/Delta M approximate to aM(-alpha)) in the mass interval 0.11 M-circle dot < M < 0.006 M-circle dot is a = +0.6 +/- 0.2. Any mass limit to formation via opacity-limited fragmentation must lie below 0.006 M-circle dot. The frequency of s Orionis brown dwarfs with circumsubstellar discs is 47 +/- 9%. Conclusions. The continuity in the mass function and in the frequency of discs suggests that very low-mass stars and substellar objects, even below the deuterium-burning mass limit, share the same formation mechanism.
Astronomy & Astrophysics
"The substellar mass function in sigma Orionis II. Optical, near-infrared and IRAC/Spitzer photometry of young cluster brown dwarfs and planetary-mass objects" (2007). Faculty Bibliography 2000s. 6902.