1998AJ....116.1301D

We examine images of the field of X1832-330, the luminous (L_X ∼ 10³⁶ ergs.s^–1) X-ray burst source near the center of the globular cluster NGC 6652, in order to identify the optical counterpart for further study. U and B ground-based images allow us to set a limit M_B0 ≳ 3.5 for the counterpart at the time of those observations, provided that the color is (U - B)₀ ∼ -1, similar to the sources known in other clusters. Archival Hubble Space Telescope observations survey most, but not all, of the 1 σ X-ray error circle and allow us to set limits M_B0 > 5.9 and M_B0 > 5.2 in the Wide Field Planetary Camera 1 (WF/PC-1) and Wide Field Planetary Camera 2 (WFPC2) regions, respectively.

In the WF/PC-1 images we do weakly detect a faint object with UV excess, but it is located 11".7 from the ROSAT X-ray position. This considerable (2.3 σ) discrepancy in position suggests that this candidate be treated with caution, but it remains the only reasonable one advanced thus far. We measure for this star m₄₃₉ = 20.2±0.2 and m₃₃₆ - m₄₃₉ = -0.5±0.2 and estimate M_B0 = 5.5 and (U - B)₀ = -0.9, similar to other known optical counterparts. If this candidate is not the identification, our limits imply that the true counterpart, not yet identified, is probably the optically faintest cluster source yet known or, alternatively, that it did not show significant UV excess at the time of these observations. Finally, we assess the outlook for the identification of the remaining luminous globular cluster X-ray sources.