1956Natur.178.1046H
1964Natur.201.1111B
1967MNRAS.137..393H
1967PASAu...1....7B
1968ARA&A...6...13B
1970MNRAS.150...45D
1970MNRAS.148..103H
1971MNRAS.151..161H
1974MNRAS.167..121H
1974MNRAS.168...93H
1977ApJ...217L..55B
1977CRASM.285..149B
1979A&A....80L..13K
1981A&A...103...28B
1981A&A...101..352V
1983A&A...120..263F
1983ApJ...268..309D
1984PASJ...36..231V
1985A&A...148..169D
1985A&A...153...91K
1986Natur.323..234D
1986A&A...165L..13T
1986A&A...166..204D
1987A&A...188..114D
1987AJ.....93.1280S
1988AJ.....95.1269M
1988ApJ...327..905S
1989ApJ...340.1103H
1989Natur.342..520M