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Published online by Cambridge University Press: 12 April 2016
R CrB at minimum light shows three type of spectra: 1) an absorption line spectrum similar to that observed at maximum light; 2) a sharp emission line spectrum mainly due to singly ionised metals which is displaced to the blue by 3 to 10 kms-1 with reference to the absorption spectrum observed at maximum. This is supposed to be a kind of permanent feature which exists even at the time of light maximum; 3) a broad emission line spectrum consisting of mainly λ3889 of Hel, H and K lines of Call and the D lines of Nal. The widths of the broad emission features indicate expansion velocity of 200 kms-1, much greater than the escape velocity (Gaposchkin 1963, Rao 1975).