A coronagraph system with unbalanced nulling interferometer and fourth-order coronagraphs
Jun Nishikawa (1), Kaito Yokochi (2), Naoshi Murakami (3), Lyu Abe (4), Takayuki Kotani (5), Motohide Tamura (1), Takashi Kurokawa (2), Alexander V. Tavrov (6), Mitsuo Takeda (7), Hiroshi Murakami (5)
(1) NAOJ; (2) TUAT; (3) Hokkaido Univ.; (4) Univ. Nice; (5) JAXA; (6) IKI; (7) UEC
We describe a four-stage coronagraph system with an unbalanced nulling interferometer (UNI). It consists of an adaptive optics (AO), the UNI, another AO for phase and amplitude correction (PAC), and a coronagraph. Here wavefront corrections and star light rejections are made twice in turn. A special feature is a magnification of the wavefront aberrations in the UNI stage which enable us to compensate for the wavefront aberrations beyond the AO systems capabilities. In experiments, we measured the aberration magnification of about 6 times by the UNI and the speckle reduction after the PAC. We are developing new two coronagraphs with a 4th-order leakage, a tandem configuration of a 3-D Sagnac nulling interferometer (common-path AIC) and an eight octant phase mask (8OPM) coronagraph, which will be used as the last stage of the system.