Journal article

Far-ultraviolet imaging of the globular cluster NGC 6681 with WFPC2

AM Watson, JR Mould, JS Gallagher, GE Ballester, CJ Burrows, S Casertano, JT Clarke, D Crisp, RE Griffiths, JJ Hester, JG Hoessel, JA Holtzman, PA Scowen, KR Stapelfeldt, JT Trauger, JA Westphal

Astrophysical Journal | Published : 1994


We have imaged the globular cluster NGC 6681 in the far-UV and visible with WFPC2 on the HST. Our far-UV images show a sparsely populated and fully resolved central region, and we detect 122 stars. The far-UV to visible color-magnitude diagram shows a well-defined horizontal branch with no evidence for hot, more evolved descendants. We find one hot horizontal-branch star significantly below the model zero-age horizontal branch, but the rest are consistent with evolutionary models within uncertainties in calibration, distance, and reddening. The center of the cluster harbors two luminous blue stragglers. Our far-UV images graphically confirm that there is no steep density gradient at small ra..

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