or stellar envelopes, as seen in Fig. . The stellar profile is more concentrated when putting this mask. If we normalize the profiles with the central value, the level of the wings has been reduced by a factor larger than 3.

to

[*3.4. High angular resolution spectroscopy*]{}

10000 Some authors have already shown the feasibility of speckle spectroscopy (Weigelt [*et al.*]{}, 1991, Kuwamura [*et al.*]{}, 1992) which has a great interest for the individual study of binary stars or for determining the physical nature of fine details found in speckle imaging. Two possibilities have been used: spectroscopy with or without a slit in the entrance image plane.

– Both the Hokudai speckle camera at the Okayama 188 cm telescope and the Steward Observatory speckle camera with the spectroscopy module at KPNO used by Kuwamura [*et al.*]{}, 1992, worked in [*objective prism spectroscopy mode*]{}, i.e., slitless spectroscopy. In this mode, the resolution is not fixed and changes as the seeing varies. The spectral calibration is rather difficult to perform since it depends upon the position of the object in the field. But the main advantage is that all the incoming light is used, without any loss.

– Weigelt [*et al.*]{}, 1991, 