Ultraviolet-excess selection of the counterpart to a globular cluster x-ray burster: Bubble Space Telescope images of the core of NGC 6712

Scott F. Anderson, Bruce Margon, Eric W. Deutsch, Ronald A. Downes

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Résumé

Using the Planetary Camera on the Hubble Space Telescope, we have obtained high spatial resolution, multicolor images and photometry of the core of the globular cluster NGC 6712. A comparison of our blue and ultraviolet images unambiguously reveals a faint (5-21), UV-excess object, "star S," within the Einstein error box for the bursting x-ray source X1850-086. The unusual color of star S is immediately apparent even in a cursory visual comparison of the images, and is more quantitatively (U-B∼-1) confirmed via photometry. A variety of different candidate optical counterparts to the x-ray source have previously been suggested from ground-based work, but our images indicate that star S is almost certainly the only viable candidate brighter than U≈21. Compared with the mean values for low mass x-ray binaries in the field, star S has a typical (U-B) color, and a moderate-to-high x-ray-to-optical luminosity ratio, but its luminosity (MB≈5) is ∼4 mag fainter than average.

langue originaleAnglais
Pages (de - à)1049-1054
Nombre de pages6
journalAstronomical Journal
Volume106
Numéro de publication3
Les DOIs
étatPublié - 1 janv. 1993
Modification externeOui

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