An Infrared Radial Velocity Search for Young Planets

过去十年的高精度径向速度研究表明，附近的主序恒星中有近12%拥有类木星行星。许多太阳系外行星(例如“热木星”)的意想不到的性质导致了对曾经被广泛接受的行星形成理论的许多修订建议。不幸的是，几乎没有观测约束来检验这些新理论。确定这些限制的最直接方法是敏感地搜索围绕低质量恒星运行的行星，这些行星的年龄与预测的行星形成时间刻度相当(不到1000万年)。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的相对模糊，更关键的是，因为与年轻恒星相关的大星斑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这项研究涉及一种新技术，使用高色散红外光谱来克服这两个观测挑战。首先，年轻的低质量恒星的红外波长更接近能量分布的峰值，因此目标恒星实际上比光学波长的恒星更亮。其次，在这些较长的波长下，恒星光球层和冷恒星黑子之间的对比度显著减弱，这(几乎是线性地)转化为这些黑子造成的径向速度噪声的减少；预测表明增益约为5倍。受此启发，怀特博士开始了对大约80颗年轻恒星(年龄不到2000万年)的红外径向速度测量。有了手头的数据，已经可以证明比100m/S更高的精度，如果存在的话，足以找到质量最大的太阳系外行星。保守的估计表明，仅改进分析技术就可以将精度提高2到3倍。这一奖项将支持首次对年轻行星的光谱红外搜索的继续，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和未来行星搜索的方式；到目前为止的结果已经帮助指导了未来高分散红外光谱设施的计划。位于亨斯特维尔的阿拉巴马大学的一名研究生研究助理也将通过该项目得到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.