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

天文学家已经发现了500多颗围绕其他恒星运行的行星。 实际上，所有这些已知的“系外行星”都是间接发现的，它们是通过行星在轨道运行过程中质量对星星的引力和拉力来推断行星的存在的。 这种牵引力可以作为星星速度的周期性变化来观察，并且可以使用连接到望远镜上的称为“光谱仪”的仪器从地球上观察到。在我们太阳系外发现的大多数行星都是“气态巨行星”，质量至少和木星一样大，而且被发现的轨道离它们的恒星很近，不太可能支持生命。但很可能有大量的行星可以做到这一点。 人们认为，这样的行星很可能像地球一样是岩石，并在“可居住带”内绕着它们的恒星运行，那里的条件允许并支持液态水的存在。这些轨道离星星足够远，由于星星的辐射，温度不会太高，但它们也不会太远，以至于任何水都会永久冻结。 因为这些行星必须在一定距离的轨道上运行，它们的恒星才能在可居住带内被发现，而且它们可能是较小的岩石行星（像地球），它们对恒星速度的影响比靠近恒星的大型气体巨星要小得多。 为了在适居带找到行星，必须使用高度精确和稳定的摄谱仪，可以非常准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，并将建造它，安装在德克萨斯州的10米口径的霍比-埃伯利望远镜上。 该摄谱仪经过精心设计，非常稳定，并具有非常精确的校准能力，能够确定微小的速度变化。 Mahadevan博士的“宜居带行星”光谱仪是由NSF的主要研究仪器计划通过天文科学部资助的。

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.