Towards asteroseismology from space, the EVRIS experiment. Opto-mechanicalcharacteristics and pointing performances of the EVRIS PAIS complex

EVRIS is the first space experiment dedicated to asteroseismology. It is de signed to measure the relative time variations of the flux of several brigh t stars and to detect their modes of pulsation. As the amplitudes of these oscillations should be very small (a few ppm), the instrument has to perfor m relative photometry with an extremely high accuracy, i.e. hundred times b etter than the classical accuracy reached from the ground. The experiment i s composed of a star tracker and a photometer, mounted on a pointing platfo rm PAIS. This paper describes the mechanical and optical design and the per formance of EVRIS, as well as the properties of the pointing system. It is shown that the EVRIS/PAIS complex meets the scientific specifications for a list of targets well suited for asteroseismology. The EVRIS collaboration is composed of: G. Epstein, J.P. Michel, F Rakotoarivelo, F Roubaud and A. Mangeney Observa toire de Paris (DESPA) 92195 Meudon, France A. Magnan, J.C. David Laboratoire d'Astronomie Spatiale, BP8 - Traverse du Siphon 13012 Marseille, France J.T. Buey Observatoire de Paris (DESPA) 92195 Meudon, France Observatoire d e Paris (DASGAL) 92195 Meudon, France Experimental Astronomy 8: 257-279, 1998. (C) 1998 Kluwer Academic Publisher s. Printed in the Netherlands.