The study of planets orbiting stars other than the Sun requires instruments of the highest performance and technology. To actually image an exoplanet, one has to greatly reduce the glare of the host star, which often outshines the reflected light off the planet by a factor of 10^7 or more. The PALM-3000 system being constructed by Dr. Richard Dekany at the California Institute of Technology plans on accomplishing these goals using an adaptive optics (AO) system of the highest order, with a 3000+ actuator deformable mirror, attached to the Palomar 5-m telescope. The region of highest sensitivity with this instrument is an unusually large 3 arcseconds in radius, allowing access to several systems whose planets have already been inferred to orbit in this zone by radial velocity studies.

Despite the modest aperture of the 5-m telescope by today's standards, the large coronagraphic field of view of the PALM-3000 is joined by a smaller actuator pitch angle and visible-light operation in making the instrument uniquely capable among AO imaging systems. The fact that significant amounts of time are available on the 5-m telescope further enhances the value of the instrument. Palomar Observatory has proven to be an excellent experimental platform for students and postdoctoral scholars to develop new AO techniques, with 21 research students and 4 postdocs since 1999, and they continue to express a commitment to hands-on training of the next-generation of astronomical researchers. Funding for this work is being provided by NSF's Division of Astronomical Sciences through its Advanced Technologies and Instrumentation program.

Project Report

Intellectual Merit We have developed the world’s most powerful system for compensating for the aberrations induced by Earth’s atmosphere for the benefit of sharper astronomical imagery. The PALM-3000 project has implemented an optical instrument on the famous 200-inch telescope at Palomar Mountain that can measure the state of Earth’s ever-changing atmosphere and apply equal-and-opposite-corrections to a thin, deformable mirror. Although this technology, known as adaptive optics, has been deployed at large telescope observatories in the past, PALM-3000 makes an unprecedented 3,888 measurements and corrections every 0.0005 seconds, allow for the first time recovery of space-telescope-like image quality, over modest fields-of-view, from the ground. In fact, PALM-3000 image quality is twice as sharp as that of the Hubble Space Telescope, though the exquisitely low background level of Hubble results in the two telescopes having comparable sensitivity, as measured in collected photons per minute. This new advance is specifically optimized for use in the direct spectroscopy study of planets orbiting stars outside our solar system, also known as exoplanets. The challenge in directly measuring the properties of these worlds, to determine their temperature, composition, and suitability for sustaining life, is that the signal from the exoplanet is terribly obscured by the bright glare of its host Sun. Since we are interested in the exoplanet and not that star, we must suppress the starlight though clever optical means while not degrading the exoplanet signal. An optical instrument known as a stellar coronagraph is used with PALM-3000 to physically block the starlight, while allowing the detection of nearby exoplanet light. In the absence of a powerful adaptive optics system, both starlight and exoplanet light would be hopelessly blurred in a fuzzball of atmospheric turbulence. Broader Impacts Throughout our project we have been pleased to have integrated hands-on astronomical research with the education of several bright young researchers. Graduate student Eduardo Bendek (University of Arizona) performed summer research on advanced topics in AO system wavefront sensing and control (2009). Daniel Filler (University of Utah) conducted independent research on the astrometric precision obtainable with ground-based adaptive optics. Caltech postdoctoral scholars Sergi Hildebrandt (now on permanent staff at Jet Propulsion Laboratory) and Christoph Baranec (now a faculty member at University of Hawaii) both contributed technical hardware components to the PALM-3000 system. Finally, it is worth crediting our talented project manager, Ms. Jennifer Roberts, who utilized this opportunity for her first experience managing a complex ground-based astronomical instrument project. Through a broad team effort of these individuals and institutions, we have enabled progress that would have been impossible individually. The PALM-3000 team would like to appreciative acknowlege the contributions of the talented and dedicated staff of Palomar Observatory. Moreover, we wish to express our gratitude for the public support for science and technology development that enabled this advance in exoplanet astronomy that is contributing to a better understanding of the Earth through the study of processes that form, influence, and determine the ultimate fate of planetary systems.

National Science Foundation (NSF)
Division of Astronomical Sciences (AST)
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Eric Bloemhof
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California Institute of Technology
United States
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