Abstract
UBV photometry of the globular cluster NGC 7099 is reported. The ultraviolet excess of δ(U–B) = 0·33 mag shows that NGC 7099 is an extremely metal-poor cluster. The colour–magnitude diagram shows a strong blue population of the horizontal branch, with very few RR Lyrae variables and stars on the red side of the instability region. The giant branch shows very little spread in colour at a given magnitude. The metallicity parameter ∆V = 3·0 mag is consistent with the low metal abundance. A reddening of E(B–V) = 0·06 mag is derived from the two-colour diagram for field stars. The relative paucity of red giants in NGC 7099 probably indicates a high helium abundance.
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