2. The substellar SACY survey

1. Figure 1 - Summary of the SACY survey 1. Introduction: The SACY project The SACY (Search for Associations Containing Young-stars) project was a spectroscopic survey to search for nearby young stars using as targets Hipparcos and TYCHO-2 stars possible counterparts of ROSAT bright X-ray sources. The LiI line, the radial velocity and the proper motions of the stars enable the detection of young nearby associations (Torres et al. 2006). In Figure 1 we show different projections of the UVW space showing the kinematicalclustering characterizing each of the young nearby association foundby the SACY survey. The table at the bottom right panel summarizes theproperties of the 9 associations detected. Column U, V and W are given inkm/s; D is the distance in parsec with their respective error; Age isgiven in Myr and N gives the number of members detected by the SACY foreach association. 3. NAOS-CONICA/VLT observations of the SACY sample We are analyzing the K-band data of the 78 SACY targets observed with NACO/VLT during 2006. As a first result, we have derived the sensitivity of the observations for several targets without companion candidates. As shown in Figure 2, we are sensitive to ΔK~7 mag at separations of 0.7” in 12 minutes of integration time. This corresponds to a 5 MJup object assuming an age of 10 Myr and using the evolutionary models by Baraffe et al. (2001). In Figure 3 we show the K-band image of a SACY target observed with NACO. The object shows a companion candidate with ~5 MJup. We have overplotted artificial companions at different separations from the central source to illustrate the sensitivity limit of the survey. Substellar companions to young, nearby stars: the SACY sampleC. A. O. Torres (LNA/MCT), N. Huélamo (Laeff-INTA), H. Bouy (UC, Berkeley), C. Melo (ESO), M Sterzik (ESO), G.R. Quast (LNA/MCT) Figure 2 - Limit of sensitivity in the K-band as a function of separation for several SACY targets. The curves were computed from the average 3-σ noise of the radial profile of the PSF. This figure shows that our 12 minutes observations are sensitive to differences of magnitude of 7 mag at 0.7”. A corresponding mass scale (for the companion) is also indicated, assuming an age of 10 Myr, and using the evolutionary models of Baraffe et al. (2001). Different colors show redundant observations. 2. The substellar SACY survey We present VLT diffraction-limited infrared images of young stars in newly discovered young nearby associations from the SACY survey. The main goal of the project is to detect substellar companions around them. Since the targets are young, low-mass stars, the contrast between the stars and the companions is reduced. Being nearby we can probe small separations. Besides the substellar companion search, the sample will allow us to study the binary frequency in each association, its evolution with age and, finally, to derive the dynamical mass of sub-stellar objects (low mass brown dwarfs and massive planets). The program has begun in 2006 with the observation of 78 targets with NACO at the VLT. In order to continue, we have submitted new proposals for NACO+ VLT and NIRI+ALTAIR at the GEMINI North. In this poster we present preliminary results for the 78 targets observed in 2006. Figure 3 - Deep K-band NACO image of a SACY object illustrating our sensitivity. "Artificial companions” with masses of 5, 7, 10 and 15 MJup have been added at increasing distances, respectively, at P.A.=270, 0, 90, and 180°, next to the central object. We are able to detect 5 MJup at separations of 0.6-0.8”, 10 MJup at separation greater than 0.6”, and any object m ore massive than 20 MJup at separations greater than 0.2”.