MRI Development: EXPRES - the Extreme Precision Spectrograph for Exoplanet Studies

在过去的二十年里，利用地面和空间观测站进行的广泛调查已经编目了太阳系以外的数千颗行星。不幸的是，大多数发现技术只能提供围绕母星星的轨道周期和行星表面的近似温度。 至关重要的是这颗行星的质量，因为这一点，再加上对它的大小的估计，导致对它的组成（岩石或气体）的粗略评估。 行星的质量是通过它们对母星星施加的引力获得的，像地球这样相对较轻的行星对恒星运动的影响很小。 事实上，要发现岩石状的类地系外行星，就需要开发出能够测量星星的周期运动的技术，这种运动的速度远远低于每秒1米，或者大约是一个人在人行道上漫步的速度。 Dr. D. Fischer（耶鲁大学）试图通过建造一种专门用于系外行星研究的仪器来实现这一目标，并将其用于亚利桑那州弗拉格斯塔夫外高山上的一台新望远镜。利用多普勒效应精确测量星星径向速度的关键是稳定性：光谱仪的温度和压力环境稳定，望远镜对仪器的照明稳定，和稳定的波长校准源。 费舍尔博士的计划包括建造一个专门为系外行星研究设计的仪器，并在望远镜上每年使用相当数量的专用夜晚。 通过将整个摄谱仪封闭在一个温度受控的真空室中，对输入图像进行光纤加扰，并使用法布里-珀罗标准具源进行校准，其通带波长最终与稳定性为10 ^11分之一的原子钟相关联，从而达到稳定性标准。 费舍尔博士希望利用这台仪器找到并描述多达100个围绕附近恒星运行的类地行星，美国国家科学基金会天文科学部通过参与重大研究仪器项目，为研制用于研究系外行星的精密仪器提供资金。该计划由数学和物理科学理事会多学科活动办公室负责。

Extensive surveys over the past two decades using ground- and space-based observatories have cataloged thousands of planets beyond our solar system. Unfortunately, most discovery techniques are able to provide little more information than the orbital period around the parent star and the approximate surface temperature of the planet. Of vital interest is the planet's mass, since this, coupled with an estimate of its size, leads to a rough assessment of its composition (rocky or gaseous). Planetary masses are obtained through the gravitational attraction they exert on the parent star, with comparatively lightweight planets like the Earth providing only feeble influences on stellar motions. Indeed, the discovery of rocky, Earthlike exoplanets requires the development of techniques that can measure periodic motions of a star well below 1 meter per second, or approximately the speed of a person strolling down a sidewalk. Dr. D. Fischer (Yale University) seeks to accomplish exactly goal this by constructing an instrument especially for exoplanet study and using it on a new telescope high in the mountains outside Flagstaff, Arizona.The key to accurate radial velocity measurements of a star using the Doppler effect is stability: a stable temperature and pressure environment for the spectrograph, stable illumination of the instrument by the telescope, and a stable wavelength calibration source. Dr. Fischer's plan includes the construction of an instrument specifically designed for exoplanet study and its use on a telescope for a sizable, dedicated number of nights each year. The stability criteria will be met by enclosing the entire spectrograph in a temperature-controlled vacuum chamber, fiber-scrambling the input image, and calibration using a Fabry-Perot etalon source whose passband wavelengths are ultimately tied to an atomic clock with a stability of one part in 10^11. Using the instrument, Dr. Fischer expects to find and characterize as many as 100 Earth-like analogs orbiting nearby stars, and for the first time obtain reliable estimates of the frequency of possible life hosts beyond our solar system.Funding for the development of a precision instrument for the study of exoplanets is being provided by NSF's Division of Astronomical Sciences through its participation in the Major Research Instrumentation program and by the Office of Multidisciplinary Activities of the Directorate for Mathematical and Physical Sciences.