Observation of inhomogeneities in the wind of the luminous red supergiant µ Cephei *
Received 20 January 1997 / Accepted 22 April 1997
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 40 km s-1 , 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 -3 , corresponding to 1-3 1016 cm 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.
Key words: stars: mass loss stars: circumstellar matter stars: µ Cep supergiants
* Based on observations made at the 3.6-m Canada-France-Hawaii telescope, operated by the National Research Council of Canada, the Centre National de la Recherche Scientifique of France, and the University of Hawaii
Send offprint requests to: N. Mauron
© European Southern Observatory (ESO) 1997
Online publication: April 20, 1998