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

We report the spectroscopic confirmation of four further whi te dwarf members of Praesepe. This brings the total number of confirmed white dwarf me mbers to eleven making this the second largest collection of these objects in an open clu ster 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 thei r 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 0.76M⊙ and their cooling ages �300Myrs. For an assumed cluster age of 625±50Myrs the infered progenitor masses are between 3.3 3.5M⊙. 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 2.7M⊙ to 6M⊙. Assuming an extrapolation of this relation to larger initi al masses is valid and adopting a maximum white dwarf mass of 1.3M⊙, our results support a minimum mass for core-collapse supernovae progenitors in the range �6.8-8.6M⊙.

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