The Gemini Planet Imager (GPI) is a high contrast imaging instrument being built for the Gemini South Telescope in Chile. The instrument will achieve high contrast at small angular separations, allowing for the direct imaging and integral field spectroscopy of extrasolar planets around nearby stars.[1] The collaboration involved in planning and building the Gemini Planet imager includes Lawrence Livermore National Lab (LLNL), the American Museum of Natural History (AMNH), the Herzberg Institute of Astrophysics, the Jet Propulsion Laboratory, the University of California, Berkeley, the University of California, Los Angeles, the University of California, Santa Cruz, the University of Montreal.[2]
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The Gemini Planet Imager will be used at the Gemini South Telescope, located in Cerro Pachon, Chile. It is expected to see first light in mid 2012, and be available for community use after commissioning in early 2013.[2] It is designed to directly detect young gas giants via their thermal emission. It will operate at near-infrared wavelengths (Y - K bands), where planets will be reasonably bright, but thermal emission from the Earth's atmosphere will not be too bright.[3]
The system consist of multiple components, including a high-order adaptive optics system, a coronagraph, a calibration interferometer, and an integral field spectrograph. The adaptive optics system, being built at LLNL, uses a MEMS deformable mirror from Boston Micromachines Corporation to correct wavefront errors induced by motion of air in the atmosphere and the optics in the telescope. The coronagraph, being built at AMNH, blocks out the light from the star being observed, which is necessary in order to see a much dimmer companion. The spectrograph, developed by UCLA and Montreal, images and takes spectra of any detected companion to the star, with a spectral resolution of 34 - 83, depending on wavelength. The expected instrument performance will allow for detection of companions one ten millionth as bright as their hosts at angular separations of roughly 0.2-1 arcseconds, down to an H band magnitude of 23.[4]
Present day searches for exoplanets are insensitive to exoplanets located at the distances from their host star comparable to the semi-major axes of the gas giants in the Solar System, greater than about 5 AU. Surveys using the radial velocity method require observing a star over at least one period of revolution, which is roughly 30 years for a planet at the distance of Saturn. Existing adaptive optics instruments become ineffective at small angular separations, limiting them to semi-major axes larger than about 30 astronomical units. The high contrast of the Gemini Planet Imager at small angular separations will allow it to detect gas giants with semi-major axes of 5-30 astronomical units.[5]
The Gemini Planet Imager will be most effective at detecting young gas giants, 1 Myr to 1 Gyr in age. The reason for this is that young planets retain heat from their formation, and only gradually cool. While a planet is still hot, it remains bright, and is thus more easily detected. This limits GPI to younger targets, but means that it will yield information about how gas giants form. In particular, the spectrograph will allow determination of the temperature and surface gravity, which yield information about the atmospheres and thermal evolution of gas giants.[5]