study, even when the atmospheric conditions were poor and did not allow any other imaging program. Hence binary measurements have been used as a backup program of all our high angular resolution observations.

[*– Stellar classification of components of binary stars*]{}

10000 When images have been restored in B, V, R, with a good photometry (cf. §5.2), color indices can be measured which then allow stellar classification of each of the two stars. This may reveal essential for the stars for which a derivation of mass has been made. Acurate orbit determination (and hence masses) are easier to perform for short-period binaries, which are generally very close and for which only global color indices or spectra are available. The individual stellar classification is then poorly known. The paradox is then that acurate masses are affected to stars with big uncertainties in the stellar classification, or less acurate masses to well identified stars, in the case of binaries with a big angular separation. Hence we see that color indices, or even spectra, of individual stars are crucial for stellar studies.

A study of composite spectrum stars (coll. J.-M. Carquillat and N. Ginestet, OMP) associate the imaging and spectroscopic modes of PISCO. 