Collaborative Research: Development of a Green-Orange Astro-comb for Exoplanet and Cosmology Research

到目前为止，已经发现了400多颗太阳系外行星的高色散光学光谱仪有一个共同的敏感性：需要超稳定、宽带、高线密度、明亮和连续的波长校准，以便能够在几周到几年的时间内精确地表征宿主恒星的微小反射速度。这些研究的一项关键技术是利用锁模飞秒脉冲激光--它在频率空间产生一组明亮的、间隔规则的发射特征--与法布里-珀罗滤光腔一起创建适当的线密度，所有这些都锁定在原子钟上，以实现长期稳定。这些所谓的“激光梳”有可能使径向速度测量达到10厘米/S的精度；因此，最终确定类地系外行星的质量应该是可能的。哈佛-史密森天体物理中心的罗纳德·沃尔斯沃斯和麻省理工学院的弗兰兹·卡尔特纳博士正计划为橙绿色光谱建造这样一个激光梳子，这个区域非常适合探测太阳类型的恒星，因此也适合探测恒星，其中一颗轨道周期约为1年的行星将存在于“生命带”，那里的地表水将以液态形式存在。该研究团队在这一领域有着良好的记录，开发了用于光学红色和蓝色光谱区域的激光梳子。新的梳子将在山上1.5米的惠普尔天文台望远镜上进行测试。并在被证明可靠的情况下，应用于Cerro Tololo洲际天文台1.5米望远镜正在进行的一个项目，该项目正在非常近的阿尔法/贝塔半人马座恒星系统中寻找绕地外运行的恒星。这项活动将包括女性科学家和学生，由此产生的时间控制激光技术的应用应该远远超出天文学。这项工作的资金是由NSF的天文科学部通过其先进技术和仪器计划提供的。

The high-dispersion optical spectrographs that have thus far enabled the discovery of more than 400 extrasolar planets have a common susceptibility: the need for ultrastable, broadband, high-line-density, bright, and continuous wavelength calibration so that the small reflex velocities of the host stars can be precisely characterized over periods of weeks to years. One crucial technology for these investigations utilizes a mode-locked femtosecond pulsed laser - which produces a bright, regularly spaced set of emission features in frequency space - together with a Fabry-Perot filtering cavity to create the appropriate line-density, all locked to an atomic clock for long-term stability. These so-called "laser combs" have the potential for enabling radial velocity measurements to a precision 10 cm/s; thus the determination of the mass of Earth-like exoplanets should eventually be possible.Dr. Ronald Walsworth of the Harvard-Smithsonian Center for Astrophysics and Dr. Franz Kaertner of the Massachusetts Institute of Technology are planning to construct such a laser comb for the orange-green spectrum, a region well-suited to the detection of solar-type stars and therefore of stars in which a planet with an orbital period of ~1 yr would exist in the "life-zone", where surface water would be in liquid form. The team of investigators has an excellent track record in this area, having developed laser combs for the optical red and blue spectral regions. The new comb will be tested at the 1.5-m Whipple Observatory telescope on Mt. Hopkins, Az, and, when proven reliable, applied to an ongoing project at the 1.5-m telescope at Cerro Tololo Interamerican Observatory that is searching for exo-Earths orbiting stars in the very nearby alpha/beta-Centaurus star system. The activity will involve both women as both scientists and students, and the resulting time-controlled laser technology should have application well beyond astronomy. Funding for this work is being provided by NSF's Division of Astronomical Sciences through its Advanced Technologies and Instrumentation program.