We report the results of a CCD imaging survey, complemented by astrometric and spectroscopic follow‐up studies, that aims to probe the fate of heavy‐weight intermediate‐mass stars by unearthing new, faint, white dwarf members of the rich, nearby, intermediate‐age open clusters NGC 3532 and NGC 2287. We identify a total of four white dwarfs with distances, proper motions and cooling times which can be reconciled with membership of these populations. We find that WD J0643−203 in NGC 2287, with an estimated mass of M= 1.02–1.16 M⊙, is potentially the most massive white dwarf so far identified within an open cluster. Guided by the predictions of modern theoretical models of the late‐stage evolution of heavy‐weight intermediate‐mass stars, we conclude that there is a distinct possibility that it has a core composed of O and Ne. We also determine that despite the cooling times of the three new white dwarfs in NGC 3532 and the previously known degenerate member NGC 3532−10 spanning ∼90 Myr, they all have remarkably similar masses (M∼ 0.9–1 M⊙). This is fully consistent with the results from our previous work on a heterogeneous sample of ∼50 white dwarfs from 12 stellar populations, on the basis of which we argued that the stellar initial–final mass relation is less steep at Minit > 4 M⊙ than in the adjacent lower initial mass regime. This change in the gradient of the relation could account for the secondary peak observed in the mass distribution of the field white dwarf population and mitigate the need to invoke close binary evolution to explain its existence. Spectroscopic investigation of numerous additional candidate white dwarf members of NGC 3532 unearthed by a recent independent study would be useful to confirm (or otherwise) these conclusions.

We present a spectroscopic component analysis of 18 candidate young, wide, non-magnetic, double-degenerate binaries identified from a search of the Sloan Digital Sky Survey Data Release 7 (DR7). All but two pairings are likely to be physical systems. We show SDSS J084952.47+471247.7 + SDSS J084952.87+471249.4 to be a wide DA + DB binary, only the second identified to date. Combining our measurements for the components of 16 new binaries with results for three similar, previously known systems within the DR7, we have constructed a mass distribution for the largest sample to date (38) of white dwarfs in young, wide, non-magnetic, double-degenerate pairings. This is broadly similar in form to that of the isolated field population with a substantial peak around M ∼ 0.6 M . We identify an excess of ultramassive white dwarfs and attribute this to the primordial separation distribution of their progenitor systems peaking at relatively larger values and the greater expansion of their binary orbits during the final stages of stellar evolution. We exploit this mass distribution to probe the origins of unusual types of degenerates, confirming a mild preference for the progenitor systems of high-field-magnetic white dwarfs, at least within these binaries, to be associated with early-type stars. Additionally, we consider the 19 systems in the context of the stellar initial mass-final mass relation. None appear to be strongly discordant with current understanding of this relationship.

We report the discovery of two, new, rare, wide, double‐degenerate binaries that each contain a magnetic and a non‐magnetic star. The components of SDSS J092646.88+132134.5 + J092647.00+132138.4 and of SDSS J150746.48+521002.1 + J150746.80+520958.0 have angular separations of only 4.6 arcsec (a∼ 650 au) and 5.1 arcsec (a∼ 750 au), respectively. They also appear to share common proper motions. Follow‐up optical spectroscopy has revealed each system to consist of a DA and a H‐rich high‐field magnetic white dwarf (HFMWD). Our measurements of the effective temperatures and the surface gravities of the DA components reveal both to have larger masses than is typical of field white dwarfs. By assuming that these degenerates have evolved essentially as single stars, owing to their wide orbital separations, we can use them to place limits on the total ages of the stellar systems. These suggest that in each case the HFMWD is probably associated with an early‐type progenitor (Minit > 2 M⊙). We find that the cooling time of SDSS J150746.80+520958.0 (DAH) is lower than might be expected had it followed the evolutionary path of a typical single star. This mild discord is in the same sense as that observed for two of the small number of other HFMWDs for which progenitor mass estimates have been made, RE J0317‐853 and EG 59. The mass of the other DAH, SDSS J092646.88+132134.5, appears to be smaller than expected on the basis of single‐star evolution. If this object was/is a member of a hierarchical triple system it may have experienced greater mass loss during an earlier phase of its life as a result of its having a close companion. The large uncertainties on our estimates of the parameters of the HFMWDs suggest that a larger sample of these objects is required to firmly identify any trends in their inferred cooling times and progenitor masses. This should shed further light on their formation and on the impact magnetic fields have on the late stages of stellar evolution. To serve as a starting point, we highlight two further candidate young, wide magnetic + non‐magnetic double‐degenerate systems within SDSS, CBS 229 and SDSS J074853.07+302543.5 + J074852.95+302543.4, which should be subjected to detailed (resolved) spectroscopic follow‐up studies.

We present an analysis of the newly resolved components of two hot, doubledegenerate systems, SDSS J074853.07+302543.5 + J074852.95+302543.4 and SDSS J150813.24+394504.9 + J150813. 31+394505.6 (CBS 229). We confirm that each system has widely separated components (a > 100 au) consisting of a H-rich, non-magnetic white dwarf and a H-rich, high-field magnetic white dwarf (HFMWD). The masses of the nonmagnetic degenerates are found to be larger than typical of field white dwarfs. We use these components to estimate the total ages of the binaries and demonstrate that both magnetic white dwarfs are the progeny of stars with M init > 2 M . We briefly discuss the traits of all known hot, wide, magnetic + non-magnetic double degenerates in the context of HFMWD formation theories. These are broadly consistent (chance probability, P ≈ 0.065) with HFMWDs forming primarily from early-type stars and, in the most succinct interpretation, link their magnetism to the fields of their progenitors. Our results do not, however, rule out that HFMWDs can form through close binary interactions and studies of more young, wide double degenerates are required to reach firm conclusions on these formation pathways.

Abstract.We present the preliminary results of a survey of the open clusters NGC3532 and NGC2287 for new white dwarf members which can help improve understanding of the form of the upper end of the stellar initial mass-final mass relation. We identify four objects with cooling times, distances and proper motions consistent with membership of these clusters. We find that despite a range in age of ∼100Myrs the masses of the four heaviest white dwarfs in NGC3532 span the narrow mass interval M W D ≈0.9−1.0M ⊙ suggesting that the initial mass-final mass relation is relatively flatter over 4.5M ⊙ < ∼ M init < ∼ 6.5M ⊙ than at immediately lower masses. Additionally, we have unearthed WD J0646-203 which is possibly the most massive cluster white dwarf identified to date. With M W D ≈1.1M ⊙ it seems likely to be composed of ONe and has a cooling time consistent with it having evolved from a single star.