1. Aiello, S., Barsella, B., Chlewicki, G., Mayo Greenberg, J., Patriarchi, P., and Perionotto, M.: 1987, Astrophysics Preprint, Arcetri 7/87.
2. Artyukhina, N. M. and Kholopov, P. N.: 1959,Soviet Astron. 6, 423.
3. Balona, L., and Crampton, D.: 1974,Monthly Notices Roy. Astron. Soc. 166, 203.
4. Barnard, E. E.: 1927,A Photographic Atlas of Selected Regions of the Milky Way, Carnegie Institute of Washington, No. 247.
5. Becker, F.: 1939,Z. Astrophys. 19, 5.