An Infrared Radial Velocity Search for Young Planets

过去十年的高精度径向速度研究表明，近12%的附近主序星拥有类木行星。许多太阳系外行星（例如“热行星”）的意外性质导致了对曾经广为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方法是对围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尺度（小于约1000万年）相当。不幸的是，传统的光学光谱技术无法做到这一点，因为年轻恒星在光学波长上相对较暗，更重要的是，因为年轻恒星的大星星斑点可以掩盖行星引起的径向速度反射运动。白色博士在这里进行的研究涉及一种新的技术，使用高色散红外光谱来克服这两个观测挑战。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它们在光学波长下更亮。第二，在这些较长的波长，恒星光球和冷星星斑点之间的对比度显着减少，这转化（几乎线性）为减少径向速度的“噪音”造成的这些斑点;预测建议的增益约为5倍。受此启发，白色博士已经开始对大约80颗年轻（年龄小于2000万年）恒星进行红外径向速度调查。有了这些数据，已经可以证明精度优于100米/秒，足以找到已知最大的太阳系外行星。 保守估计表明，仅改进分析技术就可以将精度提高2或3倍。 该奖项将支持这一首次对年轻行星进行光谱红外搜索的继续，以及这一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和未来行星搜索的方式;迄今为止的结果已经帮助指导了未来高色散红外光谱设施的计划。亨斯特维尔的亚拉巴马大学的一名研究生助理也将通过这一项目得到红外观测方面的支助和培训。

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.