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The peculiar planetary nebula in M22

Abstract

The source discovered by the IRAS satellite near the center of the globular cluster M22, IRAS 18333-2357, has been studied using the IUE satellite and a ground-based optical telescope. The northern component of the close pair of stars is not a member of the cluster. The southern component is a hot star with T_(eff) ≈ 50,000 K illuminating a small planetary nebula and is a member of M22. Both the planetary nebula and its central star are extremely hydrogen deficient. The luminosity of the central star is in good agreement with that expected on theoretical grounds and with the observed luminosity of the tip of the red giant branch

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