MRI: Development of An Airborne Infrared Spectrometer (AIR-Spec) for Coronal Emission Line Observation

日全食为科学探索和发现提供了独特的机会，也为各行各业和不同年龄的人提供了见证大自然最迷人的美丽展示之一的机会。2017年8月21日，一场罕见的日全食事件将横跨美国大陆，从俄勒冈州开始，结束于南卡罗来纳州。上一次这样的场合是在1878年7月29日。这一重大研究仪器项目的目的是设计、建造、测试和飞行一台高度先进的成像光谱仪，首次在这次日食期间测量红外光谱中的日冕。这为观测日冕打开了一个新的波长窗口，它具有促进我们对这一难以观测的区域的理解的潜力。机载红外光谱仪(AIR-SPEC)将包括一个新的图像稳定系统，使其能够部署在由国家大气研究中心(NCAR)运营的NSF湾流V飞机上。在49,000英尺以上的高度飞行，可以在不受当地天气干扰的情况下进行测量，并避免大气中的大部分吸收水蒸气，这对地面观测构成了挑战。该计划完成后，将向NCAR交付一台稳定的委托仪器，该仪器经过认证，可供其他科学家在GV上飞行，用于未来的研究任务。GV几乎可以旅行到任何地方，在未来其他日食时重新飞行显然是一个值得追求的可能性。2019年7月2日，南太平洋日食将是另一次日食飞行的第一次机会。此外，稳定的高分辨率观测能力可用于世界各地的其他太阳和大气观测实验。该项目将由史密森天体物理天文台(SAO)和NCAR高海拔天文台(HAO)的科学家和工程师合作进行，每个人都提供必要的专业知识和经验，以确保其成功完成。该项目将直接有助于培训下一代仪器科学家，同时促进多样性。工程与应用科学学院的一名哈佛研究生将参与该项目的所有方面，包括AIR-Spec仪器的设计、制造和测试，以及对观测结果的分析，如果在日食期间获得科学数据的话。这将成为她论文的基础，她将享受到来自Sao和Hao的科学家和工程师的指导。此外，预计2017年美国日食将引起公众的极大兴趣，该项目团队将与美国国家航空航天博物馆、波士顿科学博物馆和Hao的日食大电影小组的合作伙伴密切合作，开展日食前和日食后的推广活动。AIR-Spec仪器包括图像稳定系统、馈电望远镜、光栅光谱仪和狭缝颌部成像器。它将测量发射线强度、半高宽和多普勒频移，这是在2017年8月21日的“美国大日食”期间，在一系列日冕位置上的一组磁敏日冕发射线。尽管高分辨率、高灵敏度的日冕成像光谱从未在1.4至4微米之间进行过，但该光谱区域在日冕等离子体诊断、日冕空穴光谱以及作为观测日冕磁场的路径探测器方面具有巨大的潜力。红外日冕发射线非常适合于利用塞曼和汉勒效应测量磁场特性，但这种测量需要高精度的光谱-偏振仪器，在确定候选发射线的特征之前，无法设计这种仪器。2017年的日食为探测这些线提供了一个独特的机会，而AIR-SPEC观测有助于为未来的地面红外观测提供指导。2017年日食期间的Air-Spec试飞将以三个科学目标为目标：(1)在日冕多个位置的多条线路上搜索高频波。这些波可能会加热和加速太阳风。(2)识别日冕中的大尺度流动，特别是在极地冕洞中。被观测到的三条谱线在冕洞等离子体中预计会很强，因为它们部分是由散射的光球光激发的。谱线剖面分析将探索太阳风快和慢的起源。(3)补充地面日食观测，以提供整个日冕的详细等离子体诊断。Air-Spec将测量在可见光中也观察到的离子的红外发射，从而深入了解现有或计划中的光谱仪无法到达的径向距离的等离子体加热和加速。在技术方面，Air-Spec稳定系统消除了空中观测的一个重大障碍。该系统依靠惯性测量将平台在计划的0.3秒曝光时间内稳定在1.4角秒RMS(1.7角秒RMS/秒)，使其能够用于广泛的太阳和大气成像实验。最后，在未来，AIR-SPEC有可能被修改为增加用于直接测量日冕磁场方向的线偏振光学装置。

Total solar eclipses offer unique opportunities for scientific explorations and discoveries, and also for people of all walks of life and ages to witness one of Nature's most fascinating displays of beauty. On August 21, 2017, a rare total solar eclipse event will occur that will traverse the continental United States, starting in Oregon and ending in South Carolina. The previous such occasion was on 29 July 1878. The purpose of this major research instrumentation project is to design, build, test, and fly a highly advanced imaging spectrometer to make measurements during this eclipse, for the first time, of the solar corona in the infrared spectrum. This opens a new wavelength window for observation of the solar corona that has exiting potential for advancing our understanding of this hard-to-observe region. The Airborne Infra-Red Spectrometer (AIR-Spec) instrument will include a novel image stabilization system to allow it to be deployed on NSF's Gulfstream V aircraft operated by the National Center for Atmospheric Research (NCAR). Flying at an altitude above 49,000 feet makes it possible to get measurements without disturbances from local weather and avoiding most of the absorbing water vapor in the atmosphere that poses a challenge for observations at the ground. The completion of this program will see the delivery to NCAR of a stable commissioned instrument that is certified and available for other scientist to fly on the GV for future research missions. The GV can travel almost anywhere and re-flights at other future eclipses are an obvious possibility to pursue. The July 2, 2019, South Pacific eclipse will be the first chance for another eclipse flight. In addition, the stabilized high resolution observing capability can be used by other experiments for solar and atmospheric observations throughout the world.The project will be carried out in collaboration between the scientists and engineers at the Smithsonian Astrophysical Observatory (SAO) and NCAR's High Altitude Observatory (HAO), each contributing essential expertise and experience to ensure its successful completion. The project will directly contribute to training the next generation of instrumentation scientists while fostering diversity. A Harvard graduate student from the School of Engineering and Applied Sciences will be involved in all aspects of the project, including design, fabrication and test of the AIR-Spec instrument, as well as analysis of the observations, if scientific data are acquired during the eclipse. This will form the basis for her thesis and she will enjoy the benefits of mentoring from scientists and engineers at both SAO and HAO. In addition, the 2017 US solar eclipse is expected to generate a huge amount of interest amongst the general public and the project team will work closely with partners at the National Air and Space Museum, the Boston Museum of Science and the Eclipse Mega-Movie group at HAO on pre and post eclipse outreach events. The AIR-Spec instrumentation includes an image stabilization system, a feed telescope, a grating spectrometer and a slit-jaw imager. It will measure emission line intensity, FWHM, and Doppler shift a set of magnetically sensitive coronal emission lines at a range of coronal positions during the August 21, 2017 "Great American Eclipse". Although high resolution, high sensitivity coronal imaging spectroscopy has never been performed between 1.4 and 4um, this spectral region has great potential for coronal plasma diagnostics, for coronal hole spectroscopy, and as a path finder for observations of coronal magnetic fields. Infrared coronal emission lines are well suited for measuring magnetic field properties using the Zeeman and Hanle effects, but such measurements require high precision spectro-polarimetric instruments that cannot be designed until the candidate emission lines have been characterized. The 2017 eclipse provides a unique opportunity to survey these lines, and AIR-Spec observations can help provide guidance for future ground-based Infrared observations. The AIR-Spec commissioning flight during the 2017 eclipse will target three science goals: (1) Search for high frequency waves in multiple lines at multiple locations in the corona. These waves are candidates for heating and acceleration of the solar wind. (2) Identify large-scale flows in the corona, particularly in polar coronal holes. Three of the lines to be observed are expected to be strong in coronal hole plasmas because they are excited in part by scattered photospheric light. Line profile analysis will probe the origins of the fast and slow solar wind. (3) Complement ground based eclipse observations to provide detailed plasma diagnostics throughout the corona. AIR-Spec will measure IR emission of ions also observed in the visible, giving insight into plasma heating and acceleration at radial distances inaccessible with existing or planned spectrometers. On the technology side, the AIR-Spec stabilization system removes a significant obstacle to airborne observations. The system relies on inertial measurements to stabilize the platform to 1.4 arcsec RMS for the planned 0.3 sec exposure (1.7arcsec RMS per sec), allowing it to be used for a wide range of solar and atmospheric imaging experiments. Finally, for the future there is the possibility for AIR-Spec to be modified to add linear polarization optics for direct measurements of coronal magnetic field direction.