Search for sub-stellar companions of T-Tauri stars in the Lupus star-forming region

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So far, many exoplanets could already be detected indirectly on close (a < 6AU) orbits around mainly old main-sequence stars. Some brown dwarf companions were found on very wide (a > 100AU) orbits around young nearby stars by direct imaging, but very few such objects were imaged at intermediate separations between 10 up to tens of AU, up to now. We have started a high contrast imaging search campaign with NACO at ESO-VLT to directly detect such sub-stellar companions (brown dwarfs and giant planets) around young stars, not yet observed with NACO. Our target sample is chosen to maximize the detection rate, namely a few million years old T-Tauri stars in the nearby Lupus star-forming region. Because of the young age of our targets also their sub-stellar companions are young and hence self-luminous due to still ongoing contraction and accretion. We use NACO in its cube-mode to image such objects near the diffraction limit of the ESO-VLT and at larger separations. In May 2010, all our 63 targets were observed already in 1st epoch and faint sub-stellar companion-candidates were found around 58 stars with projected separations down to 21 AU. 2nd epoch follow-up imaging with NACO is scheduled in June 2011 to test the companionship of all detected candidates with astrometry. Afterwards, the sub-stellar nature of identified co-moving companions will be confirmed with follow-up photometry and spectroscopy (2012), which finally will allow us to derive the physical properties of these objects, like their effective temperatures, surface gravities, radii, and masses. Then, we can conduct a statistical test of the existence of the brown dwarf desert also at separations between ~10 and tens of AU. We will then also compare our results in Lupus with those of all other star-forming regions and associations observed previously like TWA, or Cha.