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Limits On Ionized Gas In Globular Clusters
BibTeX
@MISC{Knapp_limitson,
author = {G. R. Knapp and J. E. Gunn and P. F. Bowers and Justin F. Vasquez Por},
title = {Limits On Ionized Gas In Globular Clusters},
year = {}
}
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Abstract
Globular clusters are expected to accumulate interstellar gas due to mass loss from their stars. A sensitive search of six clusters for free-free emission from ionized gas at 8.4 GHz using the VLA failed to detect any gas, with limits well below the expected accumulation from mass loss if the gas remains in the cluster. However, simple models of the equilibrium distribution of photoionized gas show that the velocity dispersion of the gas is greater than that of the stars, and beyond 2 a critical radius the gas flows out of the cluster as a wind. The expected amounts of accumulated gas are then below the detection threshold of the observations. Fifteen radio point sources were detected in the six globular cluster fields. The majority are likely to be background sources, but five are associated with objects which are known cluster members -- four probable low-mass X-ray binaries in Pal 2, NGC 6440, NGC 6624 and NGC 7078 and the planetary nebula K 648 in NGC 7078. Two other radio source...
Keyphrases
globular cluster ionized gas radio source interstellar gas simple model gas show globular cluster field expected amount sensitive search cluster member free-free emission background source critical radius planetary nebula velocity dispersion probable low-mass x-ray binary fifteen radio point source equilibrium distribution mass loss expected accumulation detection threshold
