MRI: Development of the Habitable Zone Planet Finder Spectrograph for the Hobby-Eberly Telescope

天文学家现在已经发现了500多颗围绕其他恒星运行的行星。事实上，所有这些已知的“系外行星”都是间接发现的，它们是通过行星在运行轨道上对恒星施加的引力来推断行星的存在的。这种拉扯可以作为恒星速度的周期性变化来观察，并且可以在地球上使用连接在望远镜上的称为“摄谱仪”的仪器来观察。在我们的太阳系外发现的大多数行星都是“气态巨行星”，至少和木星一样大，它们被发现在离恒星很近的轨道上，不太可能有生命存在。但很有可能有大量的行星可以这样做。据认为，这样的行星很可能像地球一样由岩石组成，并在“宜居带”内围绕恒星运行，那里的条件允许并支持液态水的存在。这些轨道离恒星足够远，由于恒星的辐射，温度不会太高，但它们也不会太远，以至于任何水都不会永久冻结。因为这些行星必须绕轨道运行一定距离才能在宜居带找到它们的恒星，而且它们很可能是较小的岩石行星（如地球），所以它们对恒星速度的拉扯作用要比靠近恒星的大型气体巨星小得多。为了在宜居带找到行星，有必要使用高度精确和稳定的光谱仪，它可以非常精确地测量恒星速度的微小变化。宾夕法尼亚州立大学的Suvrath Mahadevan博士设计了这样一个摄谱仪，并将把它安装在德克萨斯州10米口径的霍比-埃伯利望远镜上。该光谱仪经过精心设计，非常稳定，具有非常精确的校准能力，能够确定小的速度变化。Mahadevan博士的“适居带行星发现者”光谱仪是由美国国家科学基金会天文科学部的主要研究仪器项目资助的。

Astronomers have now found over 500 planets orbiting other stars. Virtually all of these known "exoplanets" were discovered indirectly by inferring the presence of a planet by the gravitational tug and pull its mass imposes on the star during its orbit. This tug and pull can be observed as a periodic variation in the velocity of the star and can be observed from earth using an instrument called a "spectrograph" attached to a telescope. Most of the planets discovered outside our own solar system are "gas giants" at least as massive as Jupiter and have been found in close-in orbits to their stars and are not likely to be capable of supporting life. But it is very likely that there are a large number of planets that could do so. It is thought that such planets are likely to be rocky like earth and to orbit their stars within the "habitable zone" where conditions would allow and support the existence of liquid water. These orbits are far enough from the star that the temperature is not too hot due to the star's radiation but they are not so far away that any water would be permanently frozen. Because these planets must necessarily orbit at some distance for their stars to be found in the habitable zone and they are likely to be smaller rocky planets (like earth), the tug and pull they effect on their stars' velocities are considerably smaller than those of the large gas giants close to their stars. In order to find planets in the habitable zone it is necessary to use a highly precise and stable spectrograph that can very accurately measure tiny changes in the velocities of stars. Dr. Suvrath Mahadevan of Pennsylvania State University has designed such a spectrograph and will build it and put in on the 10-meter aperture Hobby-Eberly Telescope in Texas. This spectrograph is carefully designed to be extremely stable and to have a very precise calibration capability that will be able to determine small velocity changes. Dr. Mahadevan's "Habitable Zone Planet Finder" spectrograph is funded by NSF's Major Research Instrumentation program through the Division of Astronomical Sciences.