MAIA: a multispectral instrument for asteroseismology observations of hot sub dwarf stars

摘要

The Mercator Advanced Imager for Asteroseismology (MAIA) is being designed particularly for asteroseismology of hot subdwarf stars on the 1.2m Mercator Telescope. In order to achieve the required precision on the pulsation amplitude ratios, the photometric variations must be measured simultaneously in several bands with respect to constant reference stars in the field. MAIA is an optical imager to observe simultaneously in three color bands, corresponding approximately with an SDSS u, g, r+i+z photometric system. The fully dioptric design uses a common collimator, two dichroic beam splitters (cut-offs at 390nm and 550nm) and three cameras. Each camera holds a fast frame-transfer CCD cooled down to -90℃ with a compact Stirling cryocooler. All lenses are axially and radially constrained by a calibrated spring load, with radial adjustment mechanisms to calibrate the centering of each lens. The differential thermal expansion of the optical system is compensated by the thermal expansion of the different materials in the mechanical mountings, resulting in a design that is insensitive to thermal variations. Specific care has been taken to reduce the effect of manufacturing tolerances on the performance of the instrument. The tilt angle of two of the beam splitters is adjustable in two dimensions to compensate for remaining misalignment in the optical system. Finite element models have been constructed to verify that the structural flexure and structural dynamics are within the requirements. A tool has been developed to estimate the performance of the instrument based on the design parameters. Various commercial software tools have been used to optimize the workflow in this complex system design.