干旱区生态环境知识资源中心

For several years, we and others have been searching for sub-stellar companions (both brown dwarfs and giant planets) around young (up to 100 Myrs) and nearby (up to 100 PC) stars by direct imaging techniques, e.g. Speckle or AO. Here, we summarize the findings so far and derive for the first time the frequency of brown dwarfs and giant planets in wide orbits around young stars. We compare the numbers with the frequency of wide brown dwarf companions around old stars and the frequency of sub-stellar companions around nearby stars from radial velocity surveys, were many planets, but few brown dwarfs were found. We find no evidence for a brown dwarf desert at wide separations. Planets in wide separations appear to be very rare.