A search for planetary-mass objects and brown dwarfs in the Upper Scorpius association

¹ Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
² Instituto de Astrofísica de Canarias. Gran Telescopio Canarias Project, Spain e-mail: vbejar@iac.es
³ Consejo Superior de Investigaciones Científicas, Spain

Received: 11 March 2005
Accepted: 3 August 2005

Abstract

We report the results of a deep photometric search for planets and brown dwarfs in the nearby young OB Upper Scorpius association. We obtained optical (I) and near-infrared (JK_s) images around nine very low-mass stars and brown dwarf member candidates of the association, covering a total area of 113 arcmin². Using a point spread function subtraction technique, we have searched for planetary-mass companions (0.002 ) at separations as close as 3´´  from the targets. We have not found any brown dwarfs more massive than 0.030  at projected distances larger than 70 AU, or planets more massive than 0.007  at projected distances larger than 600 AU. We set an upper limit of 20% (confidence level 68.3%) to the fraction of very low-mass stars and massive brown dwarfs with planetary mass companions ( ) at physical distances larger than 600 AU. From the J, colour–magnitude diagrams and follow-up K_s-band photometry, we identify four very red objects () in the area of the survey. According to their positions in the diagram, below the expected theoretical sequence of the cluster, three are probable late M-dwarfs in the field. The faintest and reddest object () may be either a field intermediate L-dwarf with anomalously red colour at a distance of ~135 pc, an extremely red distant galaxy, or a reddened planetary-mass object in the Upper Scorpius association.