Collaborative Research: EXPRES Search for Low Mass Planets

来自耶鲁大学、洛厄尔天文台和旧金山州立大学的一个合作小组将对围绕附近恒星运行的温带小行星进行调查。几乎每一颗恒星都是由行星组成的。然而，到目前为止，探测到的行星都不像地球。许多是气态巨星，类似于木星或海王星。仅有的被探测到的小型岩石行星的轨道非常靠近它们的主恒星，那里不适宜居住的温度高达数千度。发现与地球相似的其他星球可能有助于天文学家在其他行星上发现生命。不幸的是，来自类地行星的微小信号很难探测到。这项调查将使用一种新的探测器，具有探测潜在宜居世界所需的精度。这项调查将对明亮的附近恒星进行调查，目的是探测与地球相似的行星。该项目将来自官方认可的少数族裔服务机构的本科生和硕士学生安置在系外行星研究的前沿，其中近41%的学生具有奇卡诺/墨西哥或拉丁裔背景。旧金山州立大学的学生将与耶鲁大学和洛厄尔天文台的同行合作，观察、改进RV和行星大气分析工具，并提高对行星形成的理解。学生们还将学习与讲西班牙语的公众交流这些结果，并开发可在社区外共享的材料。该项目的主要目标是在紧凑型和类似太阳系的建筑中探测低质量行星。以前的径向速度测量都错过了这些行星。这将使通过凌日和径向速度调查所看到的不同行星种群得到协调，并更好地了解行星的形成和演化。Expres光谱仪用稳定的激光频率梳进行了校准，并具有足够的精度来寻找开普勒凌日所看到的小半径行星的类似物。在接下来的三年里，通过仔细审查一组50颗高节奏的恒星，该项目将能够找到凌日调查错过的行星：这些行星的轨道周期超过100天。此外，每年近200个部分夜晚的灵活日程安排，加上非常稳定的仪器配置文件，使Rossiter-McLaughlin测量能够确定轨道倾角，并使用高色散光谱检测行星大气成分。先前RV调查的观测局限性以及探测到长周期凌日的不利可能性，使得周期超过10天的低质量行星的出现率受到很大限制。乍一看，系外行星的人口似乎不同意房车和凌日调查。径向速度精度的飞跃开辟了一个全新的参数空间，允许探测到轨道超过40天的低质量行星。很可能没有其他方法来探测这些行星--这个参数空间将不会被目前的凌日调查所探索。调查将到达参数空间，在该参数空间中，处于宜居带距离的类地行星围绕G和K恒星运行。这些高度稳定的测量还将使行星大气研究成为可能，并为恒星光球的行为提供新的见解。这项拟议的调查将增进对岩石行星出现率的了解，并在类太阳恒星周围的宜居轨道上探测类地行星。这一奖项反映了美国国家科学基金会的法定任务，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

A collaborative team from Yale University, Lowell Observatory, and San Francisco State University will conduct a survey for small, temperate planets orbiting nearby stars. Virtually every star forms with planets. However, none of the planets so far detected are like the Earth. Many are gas giants, similar to Jupiter or Neptune. The only small rocky planets that have been detected orbit very close to their host stars, where inhospitable temperatures reach thousands of degrees. The discovery of other worlds that are similar to the Earth could help astronomers to find life on other planets. Unfortunately, the tiny signals from Earth-like planets are difficult to detect. This investigation will employ a new detector with the precision needed to detect potentially habitable worlds. The investigation will carry out a survey of bright, nearby stars with the goal of detecting planets that are similar to the Earth. This program places undergraduates and masters students from an officially recognized minority serving institution, with almost 41% of students having Chicano/Mexican or Latino background, at the forefront of exoplanet research. SFSU students will be collaborating with their peers at Yale and Lowell Observatory in observing, improving RV and planet atmosphere analysis tools, and improving understanding of planet formation. Students will also be learning to communicate these results with the Spanish speaking public and developing materials that can be shared outside of their community.The primary aim of this project is to detect low mass planets in both compact and Solar System like architectures. These planets have been missed by previous radial velocity surveys. This will allow the reconciliation of different planet populations seen by transit and radial velocity surveys and to better understand planet formation and evolution. The EXPRES spectrograph is calibrated with a stable laser frequency comb and has sufficient precision to find analogs of the small radius planets seen by Kepler transits. Following a carefully vetted set of 50 stars at high cadence over the next three years will allow the project find planets missed by transit surveys: these are small planets with orbital periods longer than 100 days. In addition, flexible scheduling of nearly 200 partial nights per year coupled with a remarkably stable instrumental profile enable Rossiter-McLaughlin measurements to determine orbital obliquity and detection of planet atmosphere constituents with high dispersion spectroscopy. The observational limitations of prior RV surveys and the unfavorable probability for detection of long period transits have left the occurrence rate of low-mass planets with periods longer than 10 days poorly constrained. At first glance the exoplanet populations appear to disagree for RV and transit surveys. The leap in radial velocity precision opens up an entirely new parameter space, allowing for detection of low mass planets in orbits longer than 40 days. It is likely that there are no other ways to detect these planets - this parameter space will be unexplored by current transit surveys. The investigation will reach the parameter space where Earth-like planets at habitable zone distances orbit around G and K stars. The highly stable measurements will also enable planet atmosphere studies and provide new insights into the behavior of stellar photospheres. The proposed survey will advance understanding of rocky planet occurrence rates and detect Earth-like planets in habitable orbits around Sun-like stars.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.