Direct Imaging and Spectroscopy of Substellar Companions Next to Young Nearby Stars in TWA

Abstract

Direct imaging of substellar companions is possible since several years around nearby stars (e.g. Gl 229) and young stars (e.g. TWA-5). We are searching for brown dwarfs and giant planets as companions to stars which are both very young (up to 100 Myrs) and relatively nearby (up to 100 pc), using ground-based facilities on La Silla, Cerro Paranal, Mauna Kea, and Calar Alto with infrared imaging including speckle and adaptive optics. The young nearby association of co-moving T Tauri stars around TW Hya, called the TW Hya Association (TWA), is a prime target of our observations. We will present imaging detections of substellar companion candidates around three TWA stars and their H-band spectra, showing that they are background stars. Given all the available ground-based and space-based (HST NICMOS) data obtained so far for the TWA stars, we will discuss the frequency of young brown dwarf companions, to be compared to the frequency of old brown dwarf companions, both wide pairs from imaging surveys as well as close pairs from radial velocity surveys. We find no indications for young brown dwarf secondaries to be overabundant, so that there is no evidence that many of them get ejected during young ages.