White Dwarfs in Open Clusters: The Initial-final Mass Limit, the Supernova Mass Limit, and the White Dwarf Deficit


Kurtis A. Williams

Document Type



White dwarfs are useful tools for studying numerous interesting astrophysical phenomena. The upper limit for white dwarf progenitor masses provides a lower limits on the mass of supernova progenitors. The initial-final mass relation gives the integrated mass loss over the lifetime of a star. This dissertation presents the results from a photometric and spectroscopic study of WDs in nearby open clusters. First, a sample of nearby open clusters is constructed. Second, photometry from a subset of the sample clusters, NGC 2168, IC 4665, NGC 6633, and NGC 7063, is presented and white dwarf candidates selected. Spectroscopic follow-up of the white dwarf candidates uncovered four cluster member white dwarfs, a number far below what would be expected based on integration of the initial-mass function in the clusters. Two of the white dwarfs agree with the existing Hyades and Praesepe empirical initial-final mass relationship; a third cluster white dwarf is a suspected helium-core white dwarf. The high-mass end of the initial-final mass relation, previously determined from white dwarfs in NGC 2516 and the Pleiades, is found to be highly sensitive to the adopted ages of these clusters. The lower limit on the upper mass of main sequence parameters is reduced to 5.7 M when the age uncertainties are taken into account. Finally, a Monte Carlo simulation is used to show that the apparent lack of white dwarfs in most open cluster can be mostly explained by WDs in binary systems, the first time that this effect has been quantified.


Physics and Astronomy