RV survey for planets of brown dwarfs and very low-mass stars in ChaI

Details RV survey for planets of brown dwarfs and very low-mass stars in ChaI RV survey for planets of brown dwarfs and very low-mass stars in ChaI

2003-06-23

arxiv.org/abs/astro-ph/0306458v1

Astronomy and Astrophysics

Astrophysics

4 pages, 4 figures, proceeding of DARWIN/TPF conference, Heidelberg

Scientific paper

We have carried out a radial velocity (RV) search for planets and brown dwarf companions to very young (1-10Myr) brown dwarfs and very low-mass stars in the ChaI star forming region. This survey has been carried out with the high-resolution Echelle spectrograph UVES at the VLT. It is sensitive down to Jupiter mass planets. Out of the twelve monitored very low-mass stars and brown dwarfs, ten have constant RVs in the presented RV survey. This hints at a small multiplicity fraction of the studied population of brown dwarfs and very low-mass stars in ChaI at small separations. Upper limits for the mass Msini of possible companions have been estimated to range between 0.1 and 1.5 Jupiter masses. However, two very low-mass stars in ChaI show significant RV variations. The nature of these variations is still unclear. If caused by orbiting objects the recorded variability amplitudes would correspond to planets of the order of a few Jupiter masses. Furthermore, as a by-product of the RV survey for companions, we have studied the kinematics of the brown dwarfs in ChaI. Precise kinematic studies of young brown dwarfs are interesting in the context of the question if brown dwarfs are formed by the recently proposed ejection scenario. We have found that the RV dispersion of brown dwarfs in ChaI is only 2.2 km\s giving a first empirical upper limit for possible ejection velocities.

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