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On nitrogen abundances of planetary nebulae
(Oxford University Press (OUP), 1981)
Observations of N II recombination lines in the planetary nebula NGC 3242 are presented which allow the first temperature independent measurement of the nitrogen abundance of a nebula. Model nebula calculations are utilized ...
Observations of the Lyman limit in 19 QSOs
(Oxford University Press (OUP), 1981)
From direct spectroscopic observations of the Lyman-limit region in 32 QSOs, 19 of which are described here, we find that the covering factor for large absorbing clouds in the emission region is likely to be ϵ≲0.15. Under ...