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

Abstract

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⊙.

Testing the Initial–Final Mass Relationship of White Dwarfs

“…We have used the atmospheric parameters derived by Dobbie et al (2006). The age of the Pleiades is 125±25 Myr according to Ferrario et al (2005), which is in good agreement with the value of 119 Myr estimated by Martín et al (2001) using lithium abundances and Kband photometry of very low-mass members.…”

“…Most of the works carried out up to now have focused in studying white dwarfs in open clusters , Dobbie et al 2006, whose ages can be determined from model fits to the turn-off location in a color-magnitude diagram. One of the aims of this work is to increase the number of observational data points by studying white dwarfs in a different context, namely in common proper motion pairs, for which the total age of the system can be derived.…”

“…Consequently, any information about the metallicity of their progenitors, which has a key role in calculating the overall age of single white dwarfs is lost (progenitor lifetime plus cooling time) in the very early evolutionary stages of the cooling phase. Most of the efforts up to now have focused in the observation of white dwarfs in open clusters, since for these stellar systems there are independent measurements which allow to infer the age of the cluster and the original metallicity of the progenitors of white dwarfs Dobbie et al 2006). Open clusters have made possible the derivation of a semi-empirical initial-final mass relationship containing about 50 white dwarfs.…”

“…We have used the data of Claver et al (2001) for the Hyades and part of the Praesepe sample. We have included also two stars studied by Dobbie et al (2004) and some recent results of six new stars (Dobbie et al 2006). According to von Hippel (2005), the Hyades cluster has an age of 625±50 Myr.…”

“…Up to now, most part of the effort to improve the initial-final mass relationship from the observational point of view has been focused in observing white dwarfs in open clusters Dobbie et al 2006). This approach consists in performing spectroscopic observations of white dwarfs belonging to a cluster and deriving their atmospheric parameters (effective temperature and surface gravity) from a fit of their spectra to synthetic models.…”