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Detection of an ultraviolet and visible counterpart of the NGC 6624 X-ray burster

DOI

34

Citations

0

References

1993

Year

Ivan R. King, S. A. Stanford, R. Albrecht, C. Barbieri, J. C. Blades, A. Boksenberg, P. Crane, M. J. Disney, J. M. Deharveng, P. Jakobsen,
The Astrophysical Journal

Abstract

We have detected, in images taken with the HST FOC, the UV and optical counterpart of the X-ray source 4U 1820-30 in the globular cluster NGC 6624. Astrometric measurements place this object 2 sigma from the X-ray position of 4U 1820-30. The source dominates a far-UV FOC image and has the same flux at 1400 A as was seen through the large IUE aperture by Rich et al. (1993). It has a B magnitude of 18.7 but is not detected in V. It is 0.66 arcsec from the center of NGC 6624, a fact that may change the interpretation of the P-average of the 11 minute binary orbit. The flux drops between 1400 and 4300 A at a rate that is nearly as steep as that of a Rayleigh-Jeans curve. The flux is far too large to come from the neutron star directly but could accord with radiation from a heated accretion disk and/or the heated side of the companion star.