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Many light-curve identifications were made retrospectively from photographic plates originally obtained to patrol the sky for asteroids, supernovae and other variable phenomena. As a consequence the light curves were often incomplete so that symbiotic, cataclysmic and semi-regular variables were sometimes identified as RCBs.

RCB stars have a spectrum which resembles that of an F or G supergiant. Balmer lines are weak or absent, there are many lines of neutral atomic carbon and strong bands of molecular carbon (C2 and CN). In one of the earliest analyses of stellar surface composition, it was shown that RCrB itself was extremely hydrogen-deficient. A handful of hot RCB stars have B-type spectra. These characteristics have enabled the identification of 34 RCB stars in the Galaxy to be confirmed.

Simon Jeffery