The long-period binary AL Velorum - The atmospheric eclipse of a bright K0 giant

The properties of the AL Vel binary system, a Zeta Aur system containing a B dwarf and a bright K0 giant, are reviewed with reference to IUE observations of its atmospheric eclipse and eclipse of the accretion disk around the B-dwarf component. It is found that the conditions in the chromosphere are rather similar to those in the Zeta Aur supergiants, once allowance is made for the different sizes and scale heights involved. The conditions for Mg II suppression in the wind through ionization by the B star is discussed, and it is found that radiative excitation and subsequent ionization will suffice for the conditions encountered in the AL Vel system.