MuSCAT: a multicolor simultaneous camera for studying atmospheres of transiting exoplanets

Abstract. We report a development of a multicolor simultaneous camera for the 188-cm telescope at Okayama Astrophysical Observatory in Japan. The instrument, named MuSCAT (Multicolor Simultaneous Camera for studying Atmospheres of Transiting exoplanets), has a capability of three-color simultaneous imaging in optical wavelengths where CCDs are sensitive. MuSCAT is equipped with three 1024 × 1024 pixel CCDs which can be controlled independently. The three CCDs detect lights in g2′ (400 to 550 nm), r2′ (550 to 700 nm), and zs,2 (820 to 920 nm) bands using Astrodon Photometrics Generation 2 Sloan filters. The field of view of MuSCAT is 6.1×6.1  arc min2 with the pixel scale of 0.358  arc sec/pixel. The principal purpose of MuSCAT is to perform high-precision multicolor transit photometry. For this purpose, MuSCAT has the capability of self-autoguiding which enables it to fix the positions of stellar images within ∼1 pixel. We demonstrate relative photometric precisions of 0.101%, 0.074%, and 0.076% in g2′, r2′, and zs,2 bands, respectively, for GJ 436 (magnitudes in g′=11.81, r′=10.08, and z′=8.66) with 30-s exposures. The achieved precisions meet our objective, and the instrument is ready for operation.