Computer simulations of stellar-coronagraph observations

An infrared camera optimized for stellar coronagraphic observations is now under construction for use on the Subaru 8 m telescope. This instrument, called CIAO (Coronagraphic Imager with Adaptive Optics), aims to observe faint infrared objects in the very close vicinity of a bright source, such as brown dwarfs in binary systems and protoplanetary disks. We have conducted extensive computer simulations in order to optimize the transmittance patterns of the stellar coronagraph components and to evaluate the performance of the camera for various astronomical objects. The simulations took into account atmospheric turbulence and telescope aberration, where the wavefront is expanded in terms of Zernike polynomials. We examined the effect of the truncation of the Zernike expansion to the properties of the resultant PSFs, and found that the higher terms of the Zernike expansion omitted by former studies should be included rather in the simulation for coronagraphic observations than in the simulation for direct imaging observations. The results of the simulations show that a few minute integrations will be required for the detection of a young brown dwarf in a binary system in the Pleiades, while it will take a few nights for a protoplanetary disk in the Taurus molecular cloud.