Title: Infrared colours of brown dwarfs and low-mass stars in open clusters.
Author(s): D. Pinfield, A.C. Katsiyannis, R. Jameson, S. Hodgkin, C. Mooney (Oral)
Contact: D. Pinfield, Astrophysics Research Institute, Liverpool John Moores University

ABSTRACT
Brown dwarfs are failed stars that bridge the gap in mass between stars and planets. Never attaining high enough core temperatures to burn hydrogen like normal stars, they cool and fade over time, and become very difficult to detect. I have surveyed the young, nearby Pleiades and Praesepe open clusters (where brown dwarfs are brighter) and have identified ~40 cluster members. Near infrared J- H- and K-band measurements of these members show that the Pleiades brown dwarfs follow an unusual path in the J-H, H-K two-colour diagram. The atmospheres of such low temperature objects generally experience dust formation, which modifies their infrared opacities. However, the unusual Pleiades sequence could result from the lower surface gravities of these young contracting objects, causing a reduction in the amount of dust formation.