1
[1975, BAC 26, 82; 1977, A&A 61, 27; IAU Coll. No. 45, 293; 1980, A&A 87, 361; 1981, MNRAS 194, 705; 1993, A&A 274, 189; 1996 A&A 311, 397]
[1991, BAICz 42, 192]
[1994, MNRAS 270, 75]