Thermal Imaging of Exosolar Planets with Coronagraphic Optics for the Large Binocular Telescope

University Of Arizona, Tucson AZ

Investigators

Abstract

It is extremely difficult to be able to see a small faint object next to a much larger and much brighter object. This is the task that is faced by astronomers who would like to see a planet in orbit about its parent star. Because distances to even the nearest stars are very large, planets appear from earth to be so close to the stars that their light is lost in starlight. The traditional way of looking for faint objects next to brighter objects is to put an occulting mask (usually a circular disk) in front of the bright star. However, some of the light still manages to leak out into the area around the star due to the well-known optical phenomenon of diffraction. The light that leaks out is still much, much brighter than a planet. Dr. Matthew Kenworthy from the University of Arizona and his colleagues have demonstrated an enhanced occulting disk technique that increases the suppression of the star's light a factor of 100 by shaping the mask to cause optical interference at strategic distances from the star. A star appears to us as essentially a pin-point of light somewhat broadened by passage of the light through the earth's atmosphere. Most of the light is concentrated in the center, but some of it is spread out by the telescope optics into "Airy diffraction rings" - circles of relative brightness and darkness - around the central image of the star. By cleverly shaping the disk (termed an "apodizing phase plate") these diffraction rings can be greatly suppressed allowing fainter objects to be detected. Dr. Kenworthy is now developing an improved version of his apodizing phase plates that will suppress the diffracted light by a factor of 10,000 and will allow astronomers to detect Jupiter sized planets around nearby stars. This exciting research is supported by NSF's Division of Astronomical Sciences through the Advanced Technology and Instrumentation program.