1994A&A...290..340B

MAPPIT is an optical interferometer installed at the coude focus of the 3.9m Anglo-Australian Telescope. The instrument combines non-redundant masking with wavelength dispersion and is able to record fringes simultaneously over a wide bandwidth. For typical observations centred near 600nm, the bandwidth is {DELTA}λ=55nm and the spectral resolution is δλ=3nm. This paper describes the instrument and the data processing methods and presents some results. We find the star σ Sgr to be a close binary; the system is only partially resolved, with a separation of (11.5±2)milliarcsec (assuming the components to have equal magnitudes). We also give angular diameter measurements of two red giant stars, α Sco and β Gru. The observations of β Gru (spectral type M5 III) resolve the star for the first time and give an equivalent uniform-disk diameter of (27±3)milliarcsec.