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NGC 6791 is a well-studied, metal-rich open cluster that is so close to usthat can be imaged down to luminosities fainter than that of the termination ofits white dwarf cooling sequence, thus allowing for an in-depth study of itswhite dwarf population. We use a Monte Carlo simulator that employs up-to-dateevolutionary cooling sequences for white dwarfs with hydrogen-rich andhydrogen-deficient atmospheres, with carbon-oxygen and helium cores. Thecooling sequences for carbon-oxygen cores account for the delays introduced byboth Ne^22 sedimentation in the liquid phase and by carbon-oxygen phaseseparation upon crystallization. We do not find evidence for a substantialfraction of helium-core white dwarfs, and hence our results support thesuggestion that the origin of the bright peak of the white dwarf luminosityfunction can only be attributed to a population of unresolved binary whitedwarfs. Moreover, our results indicate that the number distribution ofsecondary masses of the population of unresolved binaries has to increase withincreasing mass ratio between the secondary and primary components of theprogenitor system. We also find that the observed cooling sequence appears tobe able to constrain the presence of progenitor sub-populations with differentchemical compositions and the fraction of non-DA white dwarfs. Our simulationsplace interesting constraints on important characteristics of the stellarpopulations of NGC 6791. In particular, we find that the fraction of singlehelium-core white dwarfs must be smaller than 5%, that a sub-population ofstars with zero metallicity must be <12%, while if the adopted metallicity ofthe sub-population is solar the upper limit is ~8%. Finally, we also find thatthe fraction of non-DA white dwarfs in this particular cluster is surprinsinglysmall <6%.

The white dwarf cooling sequence of NGC 6791: a unique tool for stellar evolution