1997A&A...326..300M

Long-slit spectrograms of the circumstellar envelope of the M2Ia luminous supergiant µ Cep are presented. This cool wind emits fluorescent KI 7665-7699Å lines and has been resolved along two north-south slits, located 5'' and 10'' west from the star. The angular resolution was ∼0.6'' . A low spectral resolution of 40km/s , i.e. about the emission line width, was used, permitting to be sensitive and to detect KI emission up 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 ∼1-3x10¹⁶cm for a distance of 830pc. The data suggest that density 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 medium. Assuming that these inhomogeneities are in fact arc-like shells ejected episodically by the star, a typical mass-loss timescale of ∼1000 years is derived.