Praesepe and the seven white dwarfs

Abstract

We report the discovery, from our preliminary survey of the Praesepe open cluster, of two new spectroscopically confirmed white dwarf candidate members. We derive the effective temperatures and surface gravities of WD0837+218 and WD0837+185 (LB5959) to be 17845-565+555 K and log g = 8.48-0.08+0.07 and 14170-1590+1380 and log g = 8.46-0.16+0.15, respectively. Using theoretical evolutionary tracks we estimate the masses and cooling ages of these white dwarfs to be 0.92 ± 0.05 M⊙ and 280-30+40 Myr and 0.90 ± 0.10 M⊙ and 500-100+170 Myr, respectively. Adopting reasonable values for the cluster age we infer the progenitors of WD0837+218 and WD0837+185 had masses of 2.6 ≤ M ≤ McritM⊙ and 2.4 ≤ M ≤ 3.5 M⊙, respectively, where Mcrit is the maximum mass of a white dwarf progenitor. We briefly discuss these findings in the context of the observed deficit of white dwarfs in open clusters and the initial mass-final mass relationship.