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Despite several decades of effort, there are very few globular cluster X-ray sources with convincing optical counterparts identified. In some cases, this may be primarily due to the extreme crowding in the cluster, which limits the utility of ground-based identification programs. As part of the FOS team's IDT program, we are taking multicolor WFPC images towards several such globular cluster X-ray sources, with the aim of resolving optical counterparts in crowded fields. We report here on initial results from WFPC images in NGC~1851.
A color-magnitude diagram from our high spatial resolution U and B WFPC images confirms the ground-based result of Auri\`ere et al. (1994, A\&A, 284, 457) that there are no markedly UV-excess objects in the X--ray error box (at least at the time the WFPC images were taken)---and that the object they denote as `X1' is among the ``best" of poor choices for the optical counterpart. However, our WFPC images reveal additional objects within the X-ray error circle, that were not resolved in the earlier ground-based images. We evaluate the plausibility of various candidate optical counterparts based on our WFPC data.
This work has been supported by NASA Grant NAG5-1630.
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