OBSERVATION OF INHOMOGENEITIES IN THE WIND OF THE LUMINOUS RED SUPERGIANT MU-CEPHEI

Long-slit spectrograms of the circumstellar envelope of the M2Ia lumin ous supergiant mu Cep are presented. This cool wind emits fluorescent KI 7665-7699 Angstrom lines and has been resolved along two north-sout h slits, located 5 '' and 10 '' west from the star. The angular resolu tion was similar to 0.6 ''. A low spectral resolution of 40 km s(-1),i .e. about the emission line width, was used, permitting to be sensitiv e and to detect KI emission up to similar to 60 '' from the star. The distributions of KI line emission along these two strips display bumps and breaks, which suggest that important inhomogeneities exist in the flow. Their apparent size is about 1 ''-3 '', corresponding to simila r to 1-3 10(16) cm for a distance of 830pc. The data suggest that dens ity contrasts of an order of magnitude occur in the wind at the above scales, although interpretation of the KI line intensity is subject to uncertainties concerning ionization and line transfer in a clumpy med ium. Assuming that these inhomogeneities are in fact are-like shells e jected episodically by the star, a typical mass-loss timescale of simi lar to 1000 years is derived.