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Possible cataclysmic variable in the core of the globular cluster 47 Tucanae

Ferraro, Francesco R.; Paresce, Francesco; de Marchi, Guido

SEVERAL globular clusters have low-luminosity X-ray sources at their cores^1-3, of which X0021.8-7221 in 47 Tucanae (NGC104) is one of the brightest. The nature of these sources is a mystery, and attempts to detect optical counterparts have been frustrated by the overcrowding of stars in cluster cores. The resolution of ground-based obse…

The O/C abundance ratio in absorbing gas clouds at high redshift

Clavel, J.; Reimers, D.; Vogel, S. +5 more

THE intrinsic extreme ultraviolet (EUV) spectrum of quasars, in which spectral lines of He and CNO ions should appear, is in most cases strongly absorbed by the hydrogen Lyman continuum of intergalactic matter at cosmological distances. The bright quasar HS1700 + 6416 (at redshift z = 2.72), from the Hamburg survey¹, is a fortuitous exc…