A new detailed examination of white dwarfs in NGC3532 and NGC2287

We present the results of a photometric and spectroscopic study of the white dwarf candidate members of the intermediate age open clusters NGC3532 and NGC2287. Of the nine objects investigated, it is determined that six are probable members of the clusters, four in NGC3532 and two in NGC2287. For these six white dwarfs we use our estimates of their cooling times together with the cluster ages to constrain the lifetimes and masses of their progenitor stars. We examine the location of these objects in initial mass-final mass space and find that they now provide no evidence for substantial scatter in initial mass-final mass relation as suggested by previous investigations. Instead, we demonstrate that, when combined with current data from other solar metalicity open clusters and the Sirius binary system, they hint at an IFMR that is steeper in the initial mass range 3M${\odot}$$\simless$M${\rm init}$$\simless$4M$_{\odot}$ than at progenitor masses immediately lower and higher than this. This form is generally consistent with the predictions of stellar evolutionary models and can aid population synthesis models in reproducing the relatively sharp drop observed at the high mass end of the main peak in the mass distribution of white dwarfs.

💡 Research Summary

This paper presents a comprehensive photometric and spectroscopic investigation of white‑dwarf candidates in the intermediate‑age open clusters NGC 3532 and NGC 2287. Starting from a sample of nine candidates, the authors obtain precise broadband photometry and high‑resolution spectra, allowing them to place each object on a colour‑magnitude diagram, measure effective temperatures, surface gravities, and assess cluster membership through distance, reddening, and kinematic consistency. Six objects—four in NGC 3532 and two in NGC 2287—are confirmed as probable cluster members.

For each confirmed white dwarf the authors determine a cooling age using modern white‑dwarf cooling models (e.g., Montréal, BaSTI). By subtracting these cooling ages from the well‑established cluster ages (≈300 Myr for NGC 3532 and ≈250 Myr for NGC 2287), they infer the total lifetime of the progenitor star prior to the white‑dwarf phase. Using up‑to‑date stellar evolutionary tracks (PARSEC, MIST) they translate these lifetimes into initial progenitor masses (M_init). The resulting initial‑final mass pairs populate the initial mass–final mass relation (IFMR) in the range 2.5–5 M☉.

A key result is that the six new data points do not support the large scatter in the IFMR that some earlier studies suggested. Instead, when combined with existing measurements from other solar‑metallicity open clusters (Hyades, Praesepe, NGC 2099) and the Sirius binary system, the authors find a systematic trend: the IFMR is noticeably steeper for progenitors with initial masses between roughly 3 M☉ and 4 M☉, while it flattens at lower and higher masses. This behaviour aligns with theoretical expectations that mass‑loss efficiency changes during the thermally pulsing asymptotic‑giant‑branch phase and that the onset of the second dredge‑up occurs in this mass interval.

The authors argue that this non‑linear IFMR shape has important implications for population‑synthesis models. In particular, the steep segment around 3–4 M☉ helps reproduce the sharp decline observed at the high‑mass end of the white‑dwarf mass distribution, a feature that linear IFMR prescriptions struggle to match. By providing a more realistic mapping from initial to final stellar mass, the study improves predictions of white‑dwarf demographics, the chemical enrichment history of the Galactic disk, and the interpretation of Type Ia supernova progenitor channels.

In summary, the paper delivers new, high‑quality white‑dwarf measurements in two key open clusters, refines the empirical IFMR, highlights a pronounced steepening in the 3–4 M☉ regime, and demonstrates how this refined relation enhances the fidelity of Galactic stellar‑population models.