Abstract
We have used deep HST WFPC2 observations of two fields in NGC 2420 to produce a cluster color-magnitude diagram down to V ≈ 27. After imposing morphological selection criteria we find eight candidate white dwarfs in NGC 2420. Our completeness estimates indicate that we have found the terminus of the WD cooling sequence. We argue that the cluster distance modulus is likely to be close to 12.10 with E(B-V) = 0.04. With these parameters we find a white dwarf cooling age for NGC 2420 of 2.0 ± 0.20 (1 σ) Gyr. The 0.20 Gyr uncertainty includes errors in the photometry, sequence fitting, precursor timescales, and theoretical white dwarf cooling timescales. Comparing the cluster white dwarf cooling age to ages derived from stellar isochrone fitting we find a preference for ages derived from models incorporating convective overshoot.
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Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.