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

到目前为止，许多系外行星已经可以间接地在主要围绕老主序恒星的近轨道上被探测到。通过直接成像，在围绕附近年轻恒星的非常宽的轨道(a&gt；100AU)上发现了一些棕矮星伴星，但到目前为止，在10到数十AU之间的中间间隔拍摄到的此类天体很少。我们已经在ESO-VLT与NACO启动了一项高对比度成像搜索活动，以直接探测年轻恒星周围尚未被NACO观测到的亚恒星同伴(褐矮星和巨行星)。我们选择的目标样本是为了最大限度地提高探测率，即附近狼星形成区域中数百万年前的T-Tauri恒星。由于我们的目标还很年轻，他们的亚恒星同伴也很年轻，因此由于仍在持续的收缩和吸积而发光。我们使用立方体模式的NACO在ESO-VLT的衍射极限附近和较大的间隔下对这类物体成像。2010年5月，我们所有的63个目标都已经在第一纪元被观测到，并在58颗恒星附近发现了微弱的亚恒星伴星-候选恒星的预测间隔降至21AU。使用NACO的第二纪元后续成像计划于2011年6月进行，以测试所有被检测到的候选者与天体测量学的相伴关系。之后，将通过后续的光度测量和光谱分析(2012)来确认已识别的共同运动伴星的亚恒星性质，这将最终使我们能够得出这些天体的物理性质，如它们的有效温度、表面引力、半径和质量。然后，我们可以对棕矮星沙漠的存在进行统计检验，间隔也在10到数十AU之间。然后，我们还将把我们在狼疮上的结果与之前观察到的所有其他恒星形成区域和星团的结果进行比较，比如TWA或Cha。

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.