1. Aikawa, T.: 1987, Astrophysics and Space Science 139, 281.
2. Aikawa, T.: 1988, Astrophysics and Space Science 149, 149.
3. Aikawa, T.: 1990, Astrophysics and Space Science 164, 295.
4. Arp, H. C.: 1955, Astronomical Journal 60, 1.
5. Baker, N. H.: 1966, in Stellar Evolution, eds. R. F. Stein and A. G. W. Cameron (New York: Plenum Press), p. 333.