An Infrared Radial Velocity Search for Young Planets

在过去的十年里，高精度的径向速度研究表明，近12%的主序星附近有类木行星。许多系外行星（例如“热木星”）的意想不到的特性导致了对曾经被广泛接受的行星形成理论的许多修订。不幸的是，几乎没有观测约束来检验这些新理论。建立这些约束的最直接的方法是对环绕低质量恒星运行的行星进行敏感的搜索，这些行星的年龄与预测的行星形成时间（小于1000万年）相当。不幸的是，传统的光谱学技术无法做到这一点，因为年轻恒星在光学波长上相对暗淡，更重要的是，因为与年轻恒星相关的大恒星黑子可以掩盖行星引起的径向速度反射运动。怀特博士将在这里进行的研究涉及一种新技术，利用高色散红外光谱来克服这两种观测挑战。首先，红外波长更接近年轻低质量恒星能量分布的峰值，因此目标恒星实际上比可见光波长更亮。其次，在这些较长的波长下，恒星光球和冷恒星黑子之间的对比明显减弱，这（几乎是线性地）转化为由这些黑子引起的径向速度“噪声”的减少；预测表明增加了大约5倍。受此启发，怀特博士开始对大约80颗年轻（年龄小于2000万年）的恒星进行红外径向速度调查。有了手头的数据，就可以证明精度超过100米/秒，如果存在的话，足以找到已知的最大质量的系外行星。保守估计表明，单独改进分析技术应该能将精度提高2到3倍。该奖项将支持对年轻行星的首次光谱红外搜索的延续，以及这项开创性的高精度红外技术的进一步发展。预计这项工作将影响下一代红外光谱仪的设计以及未来如何进行行星搜索；到目前为止，这些结果已经帮助指导了未来高色散红外光谱设施的计划。亨斯维尔阿拉巴马大学的一名研究生研究助理也将通过该项目获得红外观测方面的支持和培训。

High precision radial velocity studies over the last decade have demonstrated that nearly 12% of nearby main-sequence stars harbor Jovian-like planets. The unexpected properties of many of these extrasolar planets (e.g. the 'hot Jupiters') have resulted in many proposed revisions to the once well-accepted theory of how planets form. Unfortunately, there are few observational constraints to test these new theories. The most direct way to establish these constraints would be to conduct a sensitive search for planets orbiting low mass stars with ages comparable to the predicted planet formation timescale (less than about 10 million years). Unfortunately, traditional optical spectroscopic techniques are not able to accomplish this because of the relative faintness of young stars at optical wavelengths and, more critically, because of the large star spots associated with young stars that can mask the radial velocity reflex motion caused by a planet. The study to be carried out here by Dr. White involves a novel technique to overcome both of these observational challenges using high dispersion infrared spectroscopy. First, infrared wavelengths are much closer to the peak in the energy distribution of young low mass stars, so the target stars are effectively brighter than they are at optical wavelengths. Second, at these longer wavelengths, the contrast between the stellar photosphere and cool star spots is diminished significantly, and this translates (almost linearly) into reduced radial velocity 'noise' caused by these spots; predictions suggest a gain of a factor of about 5. Motivated by this, Dr. White has begun an infrared radial velocity survey of approximately 80 young (age less than 20 million years) stars. With the data in hand, a precision better than about 100 m/s can already be demonstrated, sufficient to find the most massive known extrasolar planets, if present. Conservative estimates show that refining the analysis techniques alone should improve the precision by a factor of 2 or 3. This award will support both the continuation of this first-ever spectroscopic infrared search for young planets, and the further development of this pioneering high precision infrared technique.It is expected that this work will influence how the next generation of infrared spectrographs is designed and how future planet searches will be conducted; the results so far have already helped guide plans for future high dispersion infrared spectroscopic facilities. A graduate research assistant at the University of Alabama in Hunstville will also be supported and trained in infrared observing through this project.