5 Results

Our findings can be summarized as follows:

H I.- The H$\alpha$ line is shown to be the most sensitive visible indicator of stellar winds in A-type supergiants. The profiles vary from pure symmetric absorption in the less luminous stars to variable emission profiles in some sources. As noted by Rosendhal (1973) the influence of luminosity upon the shape of H$\alpha$ follows a clear trend: as the luminosity increases the initially symmetric absorption profiles become asymmetric with the violet wing being more extended than the red one up to a point in which a significant emission becomes visible and then the strength of this emission component increases steadily with the luminosity. This behaviour is particularly clear for stars with the same spectral type as it is well illustrated in Fig. 4.

  

Figure 4: Evolution of the H$\alpha$ line with the luminosity of the stars

Variations in H$\alpha$ are observed in most of the A-supergiants. H$\beta$ presents a symmetric absorption profile in all the A-supergiants except in HD 12953, HD 14535, HD21389, HD 223960 and HD 223385. The only star that shows any indication of asymmetry in H$\gamma$ and H$\delta$ is HD 223960. These stars also display the strongest variations in H$\alpha$.

Ca II, Mg II (4481 Å), Na I and He I.- These lines are photospheric (symmetric absorption profiles) in all sources, no wind effects have been detected. The Ca II (H and K) and Na I D lines are strongly contaminated by the contribution from interstellar clouds. The line profiles show a complex structure with multiple components formed in absorbing regions at different velocities along the line of sight.

Mg II.- The UV resonance lines of Mg II are well known to be a sensitive indicator of wind in A-supergiants. Talavera & Gómez de Castro (1987) described the profiles and divided A-supergiants into two groups depending on these resonance ultraviolet lines profiles. The less luminous stars did not show wind effects while the luminous ones showed the evidence of mass-loss. Our observations confirm this trend. The most luminous A-supergiants present two different types of profiles characteristic of mass outflow. In some stars the Mg II lines are asymmetric with no emission feature and a sharp blue edge. In other stars the Mg II profiles are composed of several deep shortward shifted components. Variations are observed in many stars but the most spectacular profiles variations are observed in two low-luminosity stars: HD 46300 and HD 87737 where we can see the appearance and evolution of a shortward shifted component superimposed on the profile of the Mg II.

Fe II.- The Fe II spectrum of the stars showing evidence of mass-loss in H$\alpha$ is characterized by the presence of blue-shifted discrete absorption components. However not all the stars in this group present this behaviour. There are several stars whose Fe II lines are asymmetric and only slightly shortward shifted and other stars which present perfectly symmetric absorption lines. We have searched for variable components in the Fe II lines and we have detected these variations in the spectra of the most luminous stars.

Acknowledgements

We wish to thank Dr. A. Kaufer for having kindly provided unpublished optical data. We also thank the staff at VILSPA, La Palma, Calar Alto and Pic Du Midi observatories for the kind assistance during the observations. This work was partially supported by DGICYT PB93-491.