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 inst rument, called CIAO (Coronagraphic Imager with Adaptive Optics), aims to observe faint infrared objects in the very close vicinity of a brig ht source, such as brown dwarfs in binary systems and protoplanetary d isks. We have conducted extensive computer simulations in order to opt imize the transmittance patterns of the stellar coronagraph components and to evaluate the performance of the camera for various astronomica l objects. The simulations took into account atmospheric turbulence an d telescope aberration, where the wavefront is expanded in terms of Ze rnike polynomials. We examined the effect of the truncation of the Zer nike expansion to the properties of the resultant PSFs, and found that the higher terms of the Zernike expansion omitted by former studies s hould be included rather in the simulation for coronagraphic observati ons than in the simulation for direct imaging observations. The result s of the simulations show that a few minute integrations will be requi red 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 i n the Taurus molecular cloud.