Formation and Early Evolution of Brown Dwarfs in Cha I

Joergens, V., Neuhäuser, R., and Fernández, M.
Baltic Astronomy, Vol. 13, p. 505-509


We have studied a sample of very young (1--5 Myr) bona fide and candidate brown dwarfs in the Cha I star-forming cloud in terms of their kinematic properties, the occurrence of multiple systems among them as well as their rotational characteristics. Based on high-resolution spectra taken with UVES at the VLT (8.2 m), a radial velocity (RV) survey for close planetary or brown dwarf companions to the targets was carried out. No RV variability has been found hinting at a low multiplicity fraction. Upper limits for the mass {\msf M2 sin i} of possible companions range between 0.1 {\msf M {Jup}} and 2 {\msf M {Jup}}. Furthermore, the dispersion of the mean RVs of the sample was found to be only 2.2 km s{\msf -1} setting an empirical upper limit for possible ejection velocities. Finally, we have found that the brown dwarfs in Cha I are moderately fast rotators with projected rotational velocities {\msf v sin i} of 8--26 km s-1 and rotational periods of 2 to 3 days.