Collaborative Research: Infrared RV Planet Search with Externally Dispersed Interferometry II: Optimization

天文学家搜索太阳以外的恒星周围行星的最有效方法之一是试图探测行星在其轨道上绕恒星运行时恒星的速度变化。这项久经考验的技术使用了一种名为光谱仪的仪器来测量恒星光谱中特征波长的微小移位。这些漂移是由于熟悉的多普勒效应造成的，并与恒星速度的变化直接相关。但这些速度漂移非常小，为了高精度地测量它们，有必要采用某种方案来校准光谱仪中的光的波长。一种相对较新的技术是使用干涉测量法，即当两束光聚集在一起时，测量它们的“干涉”。在特定的波长，这两束光会产生条纹，条纹是根据它们的波长隔开的。通过测量这些条纹的间距，可以非常准确地确定波长。加州大学伯克利分校的曾傑瑞·埃德尔斯坦和康奈尔大学的詹姆斯·劳埃德博士正在将这项技术应用于一种不是在可见光下工作，而是在红外线下工作的光谱仪。红外光在研究比热恒星更多的较冷和较小的恒星时非常有用。发现这些恒星周围的行星将使我们对行星的实际形成和演化有一个比目前更清晰的图景。由于这些恒星比最常被研究的大质量热星更冷，它们的宜居区，即距离恒星可能适合生命开始的区域，离母星要近得多。到目前为止，大多数被发现的行星都是像木星一样的“气体巨星”，它们距离它们的恒星太远，不适合我们所知的生物存在。但有了这台新仪器，在凉爽恒星的宜居带中，可能会探测到较小的类地行星。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。

One of the most effective means employed by astronomers to search for planets around stars other than our sun is to try to detect the velocity shift of the star as the planet moves about the star in its orbit. This well proven technique employs an instrument called a spectrograph to measure the small shifts in wavelength of features in a star's spectrum. The shifts are due to the familiar Doppler effect and are directly related to the changes in the star's velocity. But these velocity shifts are very small, and in order to measure them with great accuracy it is necessary to employ some scheme to calibrate the wavelength of the light in the spectrograph. One relatively new technique is to use interferometry, measuring the "interference" of two beams of light when they come together. At a particular wavelength, the two beams of light will cause fringes to appear which are spaced according to their wavelengths. By measuring the spacing of these fringes, wavelengths can be determined very accurately.Dr. Jerry Edelstein of the University of California-Berkeley and Dr. James Lloyd of Cornell University are applying this technique to a spectrograph that works not in visual light, but in the infrared. Infrared light is very useful in the study of cooler and smaller stars which are more numerous than hot stars. Finding planets around these stars will give us a much clearer picture than we currently have of how planets are actually formed and evolve. Since these stars are cooler than the massive hot stars that have been most frequently studied, their habitable zones, the region at the distance from the star where conditions may be suitable for life to begin, are much closer to the parent star. Most of the planets discovered so far have been "gas giants" like Jupiter and are located too far from their star for biology as we know it to exist. But with this new instrument, smaller earth-like planets may be detected in the habitable zone of cool stars. Funding for this work is being provided by NSF's Division of Astronomical Sciences through its Advanced Technologies and Instrumentation program.