Reaching the End of the White Dwarf Cooling Sequence in NGC 6791

Abstract

We present new observations of the white dwarf sequence of the old open cluster NGC 6791. The brighter peak previously observed in the white dwarf luminosity function (WDLF) is now better delineated, and the second, fainter peak that we suggested earlier is now confirmed. A careful study suggests that we have reached the end of the white dwarf sequence. The WDs that create the two peaks in the WDLF show a significant turn to the blue in the color-magnitude diagram. The discrepancy between the age from the WDs and that from the main sequence turnoff remains, and we have an additional puzzle in the second peak in the WDLF. Canonical WD models seem to fail --at least at ~25%-level-- in reproducing the age of clusters of this metallicity. We discuss briefly possible ways of arriving at a theoretical understanding of the WDLF.

29 pages, 10 figures (4 in low resolution), 1 table. Accepted (2007 December 19) on ApJ

References in corpus (5)

• The Hubble Ultra Deep Field
• The Initial-Final Mass Relation: Direct Constraints at the Low Mass End
• High resolution infrared spectroscopy of the old open cluster NGC6791
• Gravitational settling of 22Ne and white dwarf evolution
• The absolute motion of the peculiar cluster NGC6791

Cited by in corpus (34)

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• Hubble Space Telescope observations of the Kepler-field cluster NGC 6819. I. The bottom of the white dwarf cooling sequence
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