1. Bok, B., 1972, “ The Birth of Stars”, Scientific American, 227,2,48
2. Boland, W. Van Woerden H., ,eds. “ Birth and Evolution of Massive Stars and Stellar Groups”, Astrophysics and Space Science Library, proc. workshop in honour of Prof. A.Blaauw, Reidel, Dordreacht, the Netherlands
3. Herbig, G., 1967 “The Youngest Stars”, Scientific American, 217,2,30
4. Tassoul, J.L., Theory of Rotating Stars, Princeton University Press, Princeton, New Jersey