An elemental abundance analysis of Vega has been performed using high-signal-to-noise 2.4 A/mm Reticon observations of the region 4313-4809 A. Vega is found to be a metal-poor star with a mean underabundance of 0.60 dex. The He/H ratio of 0.03 as derived from He I 4472 A suggests that the superficial helium convection zone has disappeared and that radiative diffusion is producing the photospheric abundance anomalies.
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Adelman et al. (1990) studied this question.