1977•The Astrophysical JournalRequires access
Optical, infrared, and X-ray observations of NGC 6624
Theodore D. Fay III, S. L. Mufson, B. J. Duncan, Rachel Hoover, P. W. Sanford, P. A. Charles, Nicholas E. White, W. Z. Wisniewski, Willem Wamsteker
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Abstract
We have observed the globular cluster NGC 6624 and the associated X-ray source 3U 1820-30 at optical, infrared, X-ray, and radio wavelengths. We find that at the center of NGC 6624 there is an extended distribution of optical and infrared emission. These observations suggest that the brightest stars populating the center of the cluster are luminous red-giant stars. We interpret the X-ray flux measurements as coming from a blackbody whose temperature varies, rising rapidly during an X-ray burst. The X-ray object, in this picture, is a spherical, collapsed object that is accreting matter. Its radius is r 47 km, and its mass is M < 15.8 M0. Subject headings: clusters: globular - infrared: sources - radio sources: general - X-rays:sources