Fiorella Castelli thanks H. Holweger for usufel discussions. She also thanks M.S. Bessell and B.J. O'Mara for having helped her to use the Anstee & O'Mara cross sections in order to compute the Van der Waals broadening parameter for Mg I b lines.
© European Southern Observatory (ESO) 1997
Online publication: July 3, 1998