Imaging Discovery of Other Worlds Around Nearby Stars

在过去的20年里，已知的系外行星数量呈指数级增长，接近1000颗。这些系外行星中的绝大多数都非常接近它们的主恒星（所谓的热木星），但其中一些是低质量的地球大小的行星，它们围绕着低质量的恒星运行，可能在系统的宜居地带，那里可能存在液态水和我们所知道的生命。虽然这些发现非常令人兴奋，但我们对这些系外行星的了解仍然非常有限，因为它们中的绝大多数都是通过间接技术发现的。要正确地描述行星的特征，需要详细的光度测定和光谱学，但由于现有仪器的限制，迄今为止，这种详细的分析只在少数几个行星上进行了。直接系外行星成像技术仍然是表征系外行星的最简单方法。当行星的光被直接探测到时，光谱仪可以用来研究行星的大气成分；估算其大气温度/光度；计算其表面重力；研究云层和岩石行星的影响；寻找生命的迹象。直接对系外行星进行成像是一项具有挑战性的工作，因为恒星/行星的角分离很小，而主恒星和行星之间的光度比很大，从温暖的年轻类木星行星的亮度比暗10万倍到类地球行星的亮度比暗数百亿倍。经过10年的发展，第一批专用的、设施级的、高度优化的系外行星成像仪器正在被运往天文台。我的团队（也是双子座行星成像仪的建设团队，GPI）已经在GPI上获得了900小时的观测时间，用于附近600颗恒星的运动，以发现和表征大约50颗新的温暖的类木星行星（比目前成像的多10倍）。通过使用星光阻挡掩膜和精确的波前控制，GPI将实现比现有仪器更深100倍的对比度，允许对年轻和附近的行星系统进行独特的观察。这项NSERC发现基金将使我能够资助两名研究生，他们将加入GPI团队进行这一激动人心的冒险。学生可以获取、减少和分析GPI数据，帮助组织活动和/或进行详细的分析，例如轨道拟合，多行星系统的稳定性研究以及搜索由云层变化产生的光度/光谱时间变化。他们的部分时间将用于进一步开发图像减法算法，并研究仪器的可能升级。学生们还将参与他们未来系外行星成像工具的设计过程，通过对计划中的30米望远镜（TMT）和太空系外行星成像望远镜（MAPLE）进行数值模拟。TMT是目前处于设计/建造阶段的下一代超大望远镜的一部分，代表着现有设施的孔径增加了3倍。TMT将达到无与伦比的分辨率，允许在太阳系尺度（< 10天文单位（AU），即10倍地日距离）直接成像类木行星。有了学生们将帮助构思的优化仪器，甚至有可能直接成像最近的低质量恒星周围的类地行星。MAPLE项目是加拿大领导的一个新的太空望远镜概念，由我领导。学生们将分析这台直径50厘米的可见波段太空望远镜的性能，直接成像最近恒星周围的超级地球/冰巨行星在最近恒星周围轨道上的反射光。通过研究这些概念获得的专业知识将适用于未来的天文台，有朝一日将拍摄类似地球的行星的照片。

Over the past 20 years, the number of known exoplanets has grown exponentially to close to 1,000. The vast majority of these exoplanets orbit very close to their primary star (the so called hot Jupiters), but a few of them are low mass Earth-size planets in orbit around lower mass stars, possibly in the systems’ habitable zones where liquid water, and life-as-we-know-it, could exist. While those discoveries are very exciting, what we know about these exoplanets is still very limited, as the vast majority of them have been discovered using indirect techniques. Detailed photometry and spectroscopy are needed to properly characterize planets, but this detailed analysis has only been conducted on a few to date due to limitations of existing instrumentation. The direct exoplanet imaging technique remains the simplest way to characterize an exoplanet. When the light of a planet is directly detected, a spectrograph can be used to: study the planet atmospheric composition; estimate its atmospheric temperature/luminosity; evaluate its surface gravity; study the effect of clouds and, for rocky planets; find signs of life. Direct exoplanet imaging is a challenging endeavor due to the small star/planet angular separation and large luminosity ratio between the host star and the planet, from 100,000 times fainter for a warm young Jupiter-like planet to tens of billion of times fainter for an Earth-like planet. After 10 years of development, a first wave of dedicated, facility-class, highly-optimized exoplanet imaging instruments is being shipped to observatories. My team (also the building team of the Gemini Planet Imager, GPI) has secured 900h of observing time on GPI for a nearby 600 stars campaign to find and characterize approximately 50 new warm Jupiter-like planets (10 times more than currently imaged). GPI will achieve 100x deeper contrast than existing instruments by the use of a starlight blocking mask and precise wavefront control, allowing a unique view of young and nearby planetary systems.This NSERC Discovery grant will enable me to fund two graduate students that will join the GPI team for this exciting adventure. The students may acquire, reduce and analyze GPI data, help organize the campaign and/or perform detailed analyses, such as orbit fitting, stability studies for multi-planet systems and search for photometric/spectroscopic time variations generated by changing cloud cover. Part of their time will be allocated to further develop the image subtraction algorithms and study possible upgrades to the instrument. The students will also participate in the design process of their future exoplanet imaging tools, by performing numerical simulations for the planned Thirty Meter Telescope (TMT) and a space exoplanet imaging telescope (MAPLE). The TMT is part of the next generation of extremely large telescopes currently in the designing/building stage, representing a 3x increase in aperture to current facilities. The TMT will achieve unparalleled resolution, allowing to directly image Jovian planets at solar system scale (< 10 astronomical units (AU), i.e. 10x the Earth-Sun separation). With optimized instruments that the students will help conceive, it may even be possible to directly image Earth-like planets around the nearest low mass stars. The project MAPLE is a new Canadian-led space telescope concept that I am leading. The students will analyze the performance of this 50 cm diameter visible-band space telescope to directly image, around the nearest stars, the reflected light of super-Earth/ice giant planets in orbit around the nearest stars. The expertise gained by studying those concepts will be applicable to future observatories that will one day take a picture of an Earth-like planet.