New praesepe white dwarfs and the initial mass-final mass relation

We report the spectroscopic confirmation of four further white dwarf members of Praesepe. This brings the total number of confirmed white dwarf members to 11, making this the second largest collection of these objects in an open cluster identified to date. This number is consistent with the high-mass end of the initial mass function of Praesepe being Salpeter in form. Furthermore, it suggests that the bulk of Praesepe white dwarfs did not gain a substantial recoil kick velocity from possible asymmetries in their loss of mass during the asymptotic giant branch phase of evolution. By comparing our estimates of the effective temperatures and the surface gravities of WD0833+194, WD0840+190, WD0840+205 and WD0843+184 to modern theoretical evolutionary tracks, we have derived their masses to be in the range 0.72–0.76 M⊙ and their cooling ages ∼300 Myr. For an assumed cluster age of 625 ± 50 Myr, the inferred progenitor masses are between 3.3 and 3.5 M⊙. Examining these new data in the context of the initial mass–final mass relation, we find that it can be adequately represented by a linear function (a₀= 0.289 ± 0.051, a₁= 0.133 ± 0.015) over the initial mass range 2.7–6 M⊙. Assuming an extrapolation of this relation to larger initial masses is valid and adopting a maximum white dwarf mass of 1.3 M⊙, our results support a minimum mass for core-collapse supernovae progenitors in the range ∼6.8–8.6 M⊙.