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Cygnus X-2 - Neutron star or degenerate dwarf?
Some conflicting models have been proposed for Cyg X-2: a degeneratedwarf model which predicts a distance of 250 + or 50 pc; and a neutronstar model which implies a distance of about 8000 pc. Based on areddening study, it is found that the distance to Cyg X-2 is greaterthan 1100 pc, which rules strongly against the degenerate dwarf model.This conclusion is based on observations of the 2200 A feature in thespectrum of Cyg X-2 made with the International Ultraviolet Explorer(IUE), and UBV and spectroscopic observations of 38 field stars. For thereddening of Cyg X-2 values of E(B-V) = 0.40 + or - 0.07 (1 sigma) arefound and are consistent with the reddening to infinity in thatdirection inferred from radio data. Consequently, Cyg X-2 may be locatedin the halo at about 8 kpc as proposed in 1979 by Cowley, Crampton, andHutchings.
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