1. Avni, Y.: 1976,Astrophys. J. 210, 642.
2. Bevington, P. R.: 1969,Data Reduction and Error Analysis for the Physical Sciences, McGraw-Hill, New York.
3. Dolan, J. F.: 1972,Astrophys. Space Sci. 17, 472.
4. Gorenstein, P. and Gursky, H.: 1968,Astrophys. J. 153, 885.
5. Hastings, N. A. J. and Peacock, J. B.: 1974,Statistical Distributions, Butterworth, London.