1. Baym, G., Pethick, C., Pines, D., and Ruderman, M., Nature, 224, 872 (1969).
2. Ruderman, M., Nature, 223, 447 (1969).
3. Baym, G., and Pines, D., Ann. Rhys., 66, 816 (1971).
4. Pines, D., and Shaham, J., Nature Physical Science, 235, 43 (1972).
5. Boynton, P. E., Groth, E., Partridge, R., and Wilkinson, D., IAU Circular, No. 2179 (1969).