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在主要围绕古老的主序星的近距离（a < 6AU）轨道上间接检测到。一些褐矮星伴星被直接成像发现在非常宽的轨道上（a > 100 Au）围绕着年轻的邻近恒星，但到目前为止，很少有这样的物体被成像在10到几十个Au之间的中间距离。我们已经开始了一个高对比度成像搜索活动与纳科在ESO-VLT直接检测这样的亚恒星同伴（褐矮星和巨行星）周围的年轻恒星，尚未观察到与纳科。我们的目标样本是为了最大限度地提高检测率而选择的，即在附近的狼星形成区域中的几百万年前的T-Tauri恒星。由于我们的目标的年轻年龄，它们的亚恒星同伴也很年轻，因此由于仍在进行的收缩和吸积而自发光。我们使用纳科在其立方模式的图像这样的对象附近的ESO-VLT的衍射极限和较大的分离。2010年5月，我们所有的63个目标都在第一个纪元被观测到，在58颗恒星周围发现了暗淡的亚恒星伴星候选者，预计分离度下降到21 Au。纳科的第二个时期的后续成像计划于2011年6月进行，以测试所有探测到的候选天体与天体测量的关系。之后，确定的同向运动伴星的亚恒星性质将通过后续的光度学和光谱学（2012）得到证实，这最终将使我们能够推导出这些物体的物理性质，如它们的有效温度，表面重力，半径和质量。然后，我们可以进行一个统计测试的棕矮星沙漠的存在，也在10和几十个Au之间的分离。然后，我们还将把我们在狼疮中的结果与以前观察到的所有其他恒星形成区域和协会（如TWA或Cha）的结果进行比较。

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.