1 Introduction

It is still an open question how brown dwarfs form. They may form like planets in disks around normal stars. The "brown dwarf desert'' is not supporting this theory unless the brown dwarfs are ejected after their formation and can now be detected as freely floating brown dwarfs. Sterzik & Durison (1999) proposed the ejection of brown dwarfs from cloud cores by three-body encounters.

Brown dwarfs may also form like stars by collapse of a cloud but do not become stars because they formed out of relatively small cores. There are several observational hints to significant circumstellar material around young brown dwarfs (e.g. Comerón et al. 2000 for ChaI) supporting a star-like formation. Recently Reipurth & Clarke (2001) proposed that brown dwarfs form by cloud fragmentation but failed to become stars because they have been ejected in the early accretion phase.

Understanding the formation of brown dwarfs is important because the number of brown dwarfs is at least equal to the number of stars (Reid et al. 1999). The ejection of a (proto-) brown dwarf in the early accretion phase or later might have left observable signs. In this paper we report on high-resolution spectroscopy of young bona fide and candidate brown dwarfs in ChaI, which indicate that there is probably no run-away brown dwarf among them.

The Chamaeleon cloud complex is comprised of three main clouds. ChaI is the most active star forming cloud among them and one of the most promising grounds for observational projects on very low-mass objects. Recently twelve low-mass M6-M8-type objects, ChaH$\alpha$1 to 12, have been detected in the center of ChaI with ages in the range of 1 to 5 Myrs (Comerón et al. 1999, 2000). Their masses are below or near the border line separating brown dwarfs and very low-mass stars. Four of them are confirmed bona fide brown dwarfs ($\sim$30 to 50  $M_{\mbox{\tiny Jup}}$) (Neuhäuser & Comerón 1998, 1999; Comerón et al. 2000).