A Search for Hot Massive Extrasolar Planets around Nearby Young Stars with the Adaptive Optics System NACO

Abstract

We report on a survey devoted for the search of exo-planets around young and nearby stars carried out with NACO at the VLT. The detection limit for 28 among the best available targets vs. the angular separation from the star is presented. The non-detection of any planetary mass companion in our survey is used to derive, for the first time, the frequency of the upper limit of the projected separation planet-stars. In particular, we find that in 50 % of cases, no 5 MJ planet (or more massive) has been detected at projected separations larger than 14 AU and no 10 MJ planet (or more massive) has been detected at projected separations larger than 8.5 AU. In 100 % of cases, these values increase to 36 AU and 65 AU respectively. The excellent sensitivity reached by our study leads to a much lower upper limit of the projected planet-star separation compared with previous studies. For example, for the Beta Pictoris group, 12 Myr), we did not detect any 10 MJ planet at distances larger than 15 AU. A previous study carried out with 4 m class telescopes put an upper limit for 10 MJ planets at ~ 60 AU. For our closest target (V 2306 Oph - d = 4.3 pc) it is shown that it would be possible to detect a 10 MJ planet at a minimum projected separation from the star of 1 AU and a 5 MJ planet at a minimum projected separation of 3.7 AU. Our results are discussed with respect to mechanisms explaining planet formation and migration and to forthcoming observational strategies and future planet finder observations from the ground.