Initial-final Mass Relation Research Articles

The Initial-Final Mass Relation from Carbon Stars in Open Clusters

Recently, Marigo et al, identified a kink in the initial-final mass relation around initial masses of Mini≈1.65−2.10M⊙, based on Gaia DR2 and EDR3 data for white dwarfs in open clusters aged 1.5–2.5 Gyr. Notably, the white dwarfs associated with this kink, all from NGC 7789, exhibit masses of ∼0.70–0.74 M⊙, usually associated with stars of Mini∼ 3–4 M⊙. This kink in the Mini mass range coincides with the theoretically accepted solar metallicity lowest-mass stars evolving into carbon stars during the AGB phase. According to Marigo et al., these carbon stars likely experienced shallow third dredge-up events, resulting in low photospheric C/O ratios and, consequently, middle stellar winds. Under such conditions, the AGB phase is prolonged, allowing for further core mass growth beyond typical predictions. If this occurs, it might provoke other anomalies, such as a non-standard surface chemical composition. We have conducted a chemical analysis of several carbon stars belonging to open clusters within the above cluster ages. Our chemical analysis reveals that the carbon stars found within the kink exhibit C/O ratios only slightly above the unity and the typical chemical composition expected for carbon stars of near solar metallicity, partially validating the above theoretical predictions. We also show that this kink in the IMFR strongly depends on the method used to derived the distances (luminosity) of these carbon stars.

The imprint of the first stars on the faint end of the white dwarf luminosity function

ABSTRACT Population III stars are characterized by extremely low metallicities as they are thought to be formed from a pristine gas in the early Universe. Although the existence of Population III stars is widely accepted, the lack of direct observational evidence hampers the study of the nature of the putative stars. In this article, we explore the possibilities of constraining the nature of the oldest stars by using the luminosity function of their remnants – white dwarfs. We study the formation and evolution of white dwarf populations by following star formation in a Milky Way-like galaxy using the semi-analytic model a-sloth. We derive the white dwarf luminosity function by applying a linear initial-final mass relation and Mestel’s cooling model. The obtained luminosity function is generally in agreement with available observations and theoretical predictions – with an exponential increase to a maximum of $M_{\mathrm{abs}} = 16$ and a sudden drop for $M_{\mathrm{abs}} \gt 16$. We explore the uncertainties of our model and compare them to the observational estimates. We adopt two different models of the initial mass function of Population III stars to show that the faint end of the luminosity function imprints the signature of Population III remnants. If the feature is detected in future observations, it would provide a clue to Population III stars and would also be an indirect evidence of low- to intermediate-mass Population III stars. We discuss the challenges and prospects for detecting the signatures.

A Test of Spectroscopic Age Estimates of White Dwarfs Using Wide WD+WD Binaries

White dwarf stars have been used for decades as precise and accurate age indicators. This work presents a test of the reliability of white dwarf total ages when spectroscopic observations are available. We conduct follow-up spectroscopy of 148 individual white dwarfs in widely separated double-white-dwarf (WD+WD) binaries. We supplement the sample with 264 previously published white dwarf spectra, as well as 1292 high-confidence white dwarf spectral types inferred from their Gaia XP spectra. We find that spectroscopic fits to optical spectra do not provide noticeable improvement to the age agreement among white dwarfs in wide WD+WD binaries. The median age agreement is ≈1.5σ for both photometrically and spectroscopically determined total ages, for pairs of white dwarfs with each having a total age uncertainty < 20%. For DA white dwarfs, we further find that photometrically determined atmospheric parameters from spectral energy distribution fitting give better total age agreement (1.0σ, 0.2 Gyr, or 14% of the binary’s average total age) compared to spectroscopically determined parameters from Balmer-line fits (agreement of 1.5σ, 0.3 Gyr, or 28% of binary’s average total age). We find further evidence of a significant merger fraction among wide WD+WD binaries: across multiple spectroscopically identified samples, roughly 20% are inconsistent with a monotonically increasing initial–final mass relation. We recommend the acquisition of an identification spectrum to ensure the correct atmospheric models are used in photometric fits in order to determine the most accurate total age of a white dwarf star.

The Role of the Third Dredge-up and Mass Loss in Shaping the Initial–Final Mass Relation of White Dwarfs

The initial–final mass relation (IFMR) plays a crucial role in understanding stellar structure and evolution by linking a star’s initial mass to the mass of the resulting white dwarf. This study explores the IFMR in the initial mass range 0.8 ≤ M ini/M ⊙ ≤ 4 using full PARSEC evolutionary calculations supplemented with COLIBRI computations to complete the ejection of the envelope and obtain the final core mass. Recent works have shown that the supposed monotonicity of the IFMR is interrupted by a kink in the initial mass range M ini ≈ 1.65–2.10 M ⊙, due to the interaction between recurrent dredge-up episodes and stellar winds in carbon stars evolving on the thermally pulsing asymptotic giant branch phase. To reproduce the IFMR nonmonotonic behavior we investigate the role of convective overshooting efficiency applied to the base of the convective envelope (f env) and to the borders of the pulse-driven convective zone (f pdcz), as well as its interplay with mass loss. We compare our models to observational data and find that f env must vary with initial mass in order to accurately reproduce the IFMR’s observed kink and slopes. We find some degeneracy between the overshooting parameters when only the IFMR information is used. Nonetheless, this analysis provides valuable insights into the internal mixing processes during the TP-AGB phase.

Measuring the initial-final mass relation using wide double white dwarf binaries from Gaia DR3

ABSTRACT The initial-final mass relation (IFMR) maps the masses of main-sequence stars to their white dwarf descendants. The most common approach to measure the IFMR has been to use white dwarfs in clusters. However, it has been shown that wide double white dwarfs can also be used to measure the IFMR using a Bayesian approach. We have observed a large sample of 90 Gaia double white dwarfs using FORS2 on the VLT. Considering 52 DA + DA, DA + DC, and DC + DC pairs, we applied our extended Bayesian framework to probe the IFMR in exquisite detail. Our monotonic IFMR is well constrained by our observations for initial masses of 1–5 M⊙, with the range of 1–4 M⊙ mostly constrained to a precision of 0.03 M⊙ or better. We add an important extension to the framework, using a Bayesian mixture-model to determine the IFMR robustly in the presence of systems departing from single star evolution. We find a large but uncertain outlier fraction of 59 ± 21 per cent, with outlier systems requiring an additional $0.70_{-0.22}^{+0.40}$ Gyr uncertainty in their cooling age differences. However, we find that this fraction is dominated by a few systems with massive components near 0.9 M⊙, where we are most sensitive to outliers, but are also able to establish four systems as merger candidates.

Initial-final mass relation from white dwarfs within 40 pc

ABSTRACT We present an initial-final mass relation derived from the spectroscopically complete volume-limited 40 pc sample of white dwarfs. The relation is modelled using population synthesis methods to derive an initial stellar population which can be fit to the observed mass distribution of white dwarfs. The population synthesis accounts for binary evolution, where higher mass white dwarfs are more likely to be merger products than their lower mass counterparts. Uncertainties are accounted from the initial mass function, stellar metallicity, and age of the Galactic disc. We also consider biases induced by the spectral type of the white dwarf where pure-hydrogen atmosphere white dwarfs are likely to have more accurate masses, whilst the full white dwarf sample will have fewer biases arising from spectral evolution. We provide a four-piece segmented linear regression using Monte Carlo methods to sample the 1-σ range of uncertainty on the initial stellar population. The derived initial-final mass relation provides a self-consistent determination of the progenitor mass for white dwarfs in the Solar neighbourhood which will be useful to study the local stellar formation history.

The unusual planetary nebula nucleus in the Galactic open cluster M37 and six further hot white dwarf candidates

Planetary nebulae in Galactic open star clusters are rare objects; only three are known to date. They are of particular interest because their distance can be determined with high accuracy, allowing one to characterize the physical properties of the planetary nebula and its ionizing central star with high confidence. Here we present the first quantitative spectroscopic analysis of a central star in an open cluster, namely the faint nucleus of IPHASX J055226.2+323724 in M37. This cluster contains 14 confirmed white dwarf members, which were previously used to study the initial-to-final-mass relation of white dwarfs, and six additional white dwarf candidates. We performed an atmosphere modeling of spectra taken with the 10m Gran Telescopio Canarias. The central star is a hot hydrogen-deficient white dwarf with an effective temperature of 90 000 K and spectral type PG1159 (helium- and carbon-rich). We know it is about to transform into a helium-rich DO white dwarf because the relatively low atmospheric carbon abundance indicates ongoing gravitational settling of heavy elements. The star belongs to a group of hot white dwarfs that exhibit ultrahigh-excitation spectral lines possibly emerging from shock-heated material in a magnetosphere. We find a relatively high stellar mass of M = 0.85−0.14+0.13 M⊙. This young white dwarf is important for the semi-empirical initial-final mass relation because any uncertainty related to white-dwarf cooling theory is insignificant with respect to the pre-white-dwarf timescale. Its post-asymptotic-giant-branch age of 170 000–480 000 yr suggests that the extended planetary nebula is extraordinarily old. We also performed a spectroscopic analysis of the six other white dwarf candidates of M37, confirming one as a cluster member.

Uncovering new white dwarf–open cluster associations using Gaia DR3

Context. Open clusters (OCs) provide homogeneous samples of white dwarfs (WDs) with known distances, extinctions, and total ages. The unprecedented astrometric precision of Gaia allows us to identify many novel OC–WD pairs. Studying WDs in the context of their parent OCs makes it possible to determine the properties of WD progenitors and study the initial–final mass relation (IFMR). Aims. We seek to find potential new WD members of OCs in the solar vicinity. The analysis of OC members’ parallaxes allows us to determine the OC distances to a high precision, which in turn enables us to calculate WD masses and cooling ages and to constrain the IFMR. Methods. We searched for new potential WD members of nearby OCs using the density-based machine learning clustering algorithm HDBSCAN. The clustering analysis was applied in five astrometric dimensions – positions in the sky, proper motions and parallaxes, and in three dimensions where the positional information was not considered in the clustering analysis. The identified candidate OC WDs were further filtered using the photometric criteria and properties of their putative host OCs. The masses and cooling ages of the WDs were calculated via a photometric method using all available Gaia, Pan-STARRS, SDSS, and GALEX photometry. The WD progenitor masses were determined using the ages and metallicities of their host OCs. Results. Altogether, 63 OC WD candidates were recovered, 27 of which are already known in the literature. We provide characterization for 36 novel WDs that have significant OC membership probabilities. Six of them fall into relatively unconstrained sections of the IFMR where the relation seems to exhibit nonlinear behavior. We were not able to identify any WDs originating from massive progenitors that would even remotely approach the widely adopted WD progenitor mass limit of 8 M⊙; this confirms the paucity of such objects residing in OCs and hints at a presence of velocity kicks for nascent WDs.

Evolution of low mass population III stars from the pre-main sequence to the white dwarf cooling track

ABSTRACT Radiation feedback from massive population III stars may have given rise to low mass star formation from primordial or nearly primordial material. If early Universe low mass stars did form, some should remain locally as white dwarfs, sub-giants, or main sequence stars. In this paper, we present model calculations for the evolution of single 0.8–3.0 M⊙ stars with primordial metallicity from pre-main sequence to the white dwarf cooling track, and calculations for the evolution of single 4.0–7.0 M⊙ stars which conclude in the giant phase. One goal of this work is to identify potential observable markers for potential observed progenitors of first or nearly first stars. We uncover a number of seemingly peculiar evolutionary differences between that of population III low mass stars compared with younger higher Z stars, as well as compared to other primordial evolution models. We also present an initial–final mass relationship and identify the minimum mass of a single white dwarf that could have had a population III progenitor.

Dynamical masses and ages of Sirius-like systems

ABSTRACT We measure precise orbits and dynamical masses and derive age constraints for six confirmed and one candidate Sirius-like systems, including the Hyades member HD 27483. Our orbital analysis incorporates radial velocities, relative astrometry, and Hipparcos–Gaia astrometric accelerations. We constrain the main-sequence lifetime of a white dwarf’s progenitor from the remnant’s dynamical mass and semi-empirical initial–final mass relations and infer the cooling age from mass and effective temperature. We present new relative astrometry of HD 27483 B from Keck/NIRC2 observations and archival Hubble Space Telescope data, and obtain the first dynamical mass of ${0.798}_{-0.041}^{+0.10}$ M⊙, and an age of ${450}_{-180}^{+570}$ Myr, consistent with previous age estimates of Hyades. We also measure precise dynamical masses for HD 114174 B (0.591 ± 0.011 M⊙) and HD 169889 B (${0.526}_{-0.037}^{+0.039}$ M⊙), but their age precisions are limited by their uncertain temperatures. For HD 27786 B, the unusually small mass of 0.443 ± 0.012 M⊙ suggests a history of rapid mass-loss, possibly due to binary interaction in its progenitor’s asymtotic giant branch phase. The orbits of HD 118475 and HD 136138 from our radial velocity fitting are overall in good agreement with Gaia DR3 astrometric two-body solutions, despite moderate differences in the eccentricity and period of HD 136138. The mass of ${0.580}_{-0.039}^{+0.052}$ M⊙ for HD 118475 B and a speckle imaging non-detection confirms that the companion is a white dwarf. Our analysis shows examples of a rich number of precise WD dynamical mass measurements enabled by Gaia DR3 and later releases, which will improve empirical calibrations of the white dwarf initial–final mass relation.

The Impact of Initial–Final Mass Relations on Black Hole Microlensing

Uncertainty in the initial–final mass relation (IFMR) has long been a problem in understanding the final stages of massive star evolution. One of the major challenges of constraining the IFMR is the difficulty of measuring the mass of nonluminous remnant objects (i.e., neutron stars and black holes). Gravitational-wave detectors have opened the possibility of finding large numbers of compact objects in other galaxies, but all in merging binary systems. Gravitational lensing experiments using astrometry and photometry are capable of finding compact objects, both isolated and in binaries, in the Milky Way. In this work we improve the Population Synthesis for Compact object Lensing Events (PopSyCLE) microlensing simulation code in order to explore the possibility of constraining the IFMR using the Milky Way microlensing population. We predict that the Roman Space Telescope’s microlensing survey will likely be able to distinguish different IFMRs based on the differences at the long end of the Einstein crossing time distribution and the small end of the microlensing parallax distribution, assuming the small (π E ≲ 0.02) microlensing parallaxes characteristic of black hole lenses are able to be measured accurately. We emphasize that future microlensing surveys need to be capable of characterizing events with small microlensing parallaxes in order to place the most meaningful constraints on the IFMR.

New DA white dwarf models for asteroseismology of ZZ Ceti stars

Context. Asteroseismology is a powerful tool used to infer the evolutionary status and chemical stratification of white dwarf stars and to gain insights into the physical processes that lead to their formation. This is particularly true for the variable hydrogen-rich atmosphere (DA) white dwarfs, known as DAV or ZZ Ceti stars. They constitute the most numerous class of pulsating white dwarfs. Aims. We present a new grid of white dwarf models that take into account advances made over the last decade in modeling and input physics of both the progenitor and the white dwarf stars. As a result, it is possible to avoid several shortcomings present in the set of white dwarf models employed in the asteroseismological analyses of ZZ Ceti stars that we carried out in our previous works. Methods. We generate white dwarf stellar models appropriate for ZZ Ceti stars with masses from ∼0.52 to ∼0.83 M⊙, resulting from the whole evolution of initially 1.5–4.0 M⊙ mass star models. These new models are derived from a self-consistent way with the changes in the internal chemical distribution that result from the mixing of all the core chemical components induced by mean molecular-weight inversions, from 22Ne diffusion, Coulomb sedimentation, and from residual nuclear burning. In addition, the expected nuclear-burning history and mixing events along the progenitor evolution are accounted for, in particular the occurrence of third dredge-up, which determines the properties of the core and envelope of post-AGB and white dwarf stars, as well as the white dwarf initial-final mass relation. The range of hydrogen envelopes of our new ZZ Ceti models extends from the maximum residual hydrogen content predicted by the progenitor history, log(MH/M⊙)∼ − 4 to −5, to log(MH/M⊙) = − 13.5, thus allowing for the first stellar models that would enable the search for seismological solutions for ZZ Ceti stars with extremely thin hydrogen envelopes – if, indeed, they do exist in nature. We computed the adiabatic gravity(g)-mode pulsation periods of these models. Calculations of our new evolutionary and pulsational ZZ Ceti models were performed with the LPCODE stellar evolution code and the LP-PUL stellar pulsation code. Results. Our new hydrogen-burning post-AGB models predict chemical structures for ZZ Ceti stars that are substantially different from those we used in our previous works, particularly in connection with the chemical profiles of oxygen and carbon near the stellar centre. We also discuss the implications of these new models for the pulsational spectrum of ZZ Ceti stars. Specifically, we find that the pulsation periods of g modes and the mode-trapping properties of the new models differ significantly from those characterizing the ZZ Ceti models of our previous works, particularly for long periods. Conclusions. The improvements in the modeling of ZZ Ceti stars we present here lead to substantial differences in the predicted pulsational properties of ZZ Ceti stars, which are expected to impact the asteroseismological inferences of these stars. This is extremely relevant in view of the abundant amount of photometric data from current and future space missions, resulting in discoveries of numerous ZZ Ceti stars.

WDPhotTools – a white dwarf photometric toolkit in Python

Abstract From data collection to photometric fitting and analysis of white dwarfs, to generating a white dwarf luminosity function requires numerous astrophysical, mathematical, and computational domain knowledge. The steep learning curve makes it difficult to enter the field, and often individuals have to reinvent the wheel to perform identical data reduction and analysis tasks. We have gathered a wide range of publicly available white dwarf cooling models and synthetic photometry to provide a toolkit that allows (i) visualization of various models, (ii) photometric fitting of a white dwarf with or without distance and reddening, and (iii) the computing of white dwarf luminosity functions with a choice of initial mass function, main-sequence evolution model, star-formation history, initial–final mass relation, and white dwarf cooling model. We have recomputed and compared the effective temperature of the white dwarfs from the Gaia EDR3 white dwarf catalogue. The two independent works show excellent agreement in the temperature solutions.

The Initial-Final Mass Relation of White Dwarfs: A Tool to Calibrate the Third Dredge-Up

The initial mass-final mass relationship (IFMR) of white dwarfs (WD) represents a crucial benchmark for stellar evolution models, especially for the efficiency of mixing episodes and mass loss during the asymptotic giant branch (AGB) phase. In this study, we argue that this relation offers the opportunity to constrain the third dredge-up (3DU), with important consequences for chemical yields. The results are discussed in light of recent studies that have identified a kink in the IFMR for initial masses close to 2M⊙. Adopting a physically-sound approach in which the efficiency λ of the 3DU varies as a function of core and envelope masses, we calibrate λ in solar-metallicity TP-AGB models in order to reproduce the final masses of their WD progeny, over the range of initial masses 0.9≤Mi/M⊙≤6. In particular, we find that in low-mass stars with 1.4≲Mi/M⊙≲2.0 the efficiency is small, λ≤0.3, it steeply rises to about λ≃0.65 in intermediate-mass stars with 2.0≤Mi/M⊙≤4.0, and then it drops in massive TP-AGB stars with 4.0≲Mi/M⊙≲6.0. Our study also suggests that a second kink may show up in the IFMR at the transition between the most massive carbon stars and those that are dominated by hot-bottom burning.

A Fresh Look at AGB Stars in Galactic Open Clusters with Gaia: Impact on Stellar Models and the Initial–Final Mass Relation

Abstract Benefiting from the Gaia second and early third releases of photometric and astrometric data, we examine the population of asymptotic giant branch (AGB) stars that appear in the fields of intermediate-age and young open star clusters. We identify 49 AGB star candidates, brighter than the tip of the red giant branch, with a good to high cluster membership probability. Among them, we find 19 TP-AGB stars with known spectral type: 4 M stars, 3 MS/S stars, and 12 C stars. By combining observations, stellar models, and radiative transfer calculations that include the effect of circumstellar dust, we characterize each star in terms of initial mass, luminosity, mass-loss rate, core mass, period, and mode of pulsation. The information collected helps us shed light on the TP-AGB evolution at solar-like metallicity, placing constraints on the third dredge-up process, the initial masses of carbon stars, stellar winds, and the initial–final mass relation (IFMR). In particular, we find that two bright carbon stars, MSB 75 and BM IV 90, members of the clusters NGC 7789 and NGC 2660 (with similar ages of ≃ 1.2–1.6 Gyr and initial masses 2.1 ≳ M i /M ⊙ ≳ 1.9), have unusually high core masses, M c ≈ 0.67–0.7 M ⊙. These results support the findings of a recent work (Marigo et al. 2020) that identified a kink in the IFMR, which interrupts its monotonic trend just at the same initial masses. Finally, we investigate two competing scenarios to explain the M c data: the role of stellar winds in single-star evolution, and binary interactions through the blue straggler channel.

The updated basti stellar evolution models and isochrones – III. White dwarfs

ABSTRACT We present new cooling models for carbon–oxygen white dwarfs (WDs) with both H- and He-atmospheres, covering the whole relevant mass range, to extend our updated basti (a Bag of Stellar Tracks and Isochrones) stellar evolution archive. They have been computed using core chemical stratifications obtained from new progenitor calculations, adopting a semi-empirical initial–final mass relation. The physics inputs have been updated compared to our previous basti calculations: 22Ne diffusion in the core is now included, together with an updated CO phase diagram, and updated electron conduction opacities. We have calculated models with various different neon abundances in the core, suitable to study WDs in populations with metallicities ranging from supersolar to metal poor, and have performed various tests/comparisons of the chemical stratification and cooling times of our models. Two complete sets of calculations are provided, for two different choices of the electron conduction opacities, to reflect the current uncertainty in the evaluation of the electron thermal conductivity in the transition regime between moderate and strong degeneracy, crucial for the H- and He-envelopes. We have also made a first, preliminary estimate of the effect – that turns out to be generally small – of Fe sedimentation on the cooling times of WD models, following recent calculations of the phase diagrams of carbon–oxygen-iron mixtures. We make publicly available the evolutionary tracks from both sets of calculations, including cooling times and magnitudes in the Johnson-Cousins, Sloan, Pan-STARSS, GALEX, Gaia-DR2, Gaia-eDR3, HST-ACS, HST-WFC3, and JWST photometric systems.

The Initial–Final Mass Relation for Hydrogen-deficient White Dwarfs*

Abstract The initial–final mass relation represents the total mass lost by a star during the entirety of its evolution from the zero age main sequence to the white-dwarf cooling track. The semiempirical initial–final mass relation (IFMR) is largely based on observations of DA white dwarfs, the most common spectral type of white dwarf and the simplest atmosphere to model. We present a first derivation of the semiempirical IFMR for hydrogen-deficient (non-DA) white dwarfs in open star clusters. We identify a possible discrepancy between the DA and non-DA IFMRs, with non-DA white dwarfs ≈0.07 M ⊙ less massive at a given initial mass. Such a discrepancy is unexpected based on theoretical models of non-DA formation and observations of field white dwarf mass distributions. If real, the discrepancy is likely due to enhanced mass loss during the final thermal pulse and renewed post-AGB evolution of the star. However, we are dubious that the mass discrepancy is physical and instead is due to the small sample size, to systematic issues in model atmospheres of non-DAs, and to the uncertain evolutionary history of Procyon B (spectral type DQZ). A significantly larger sample size is needed to test these assertions. In addition, we also present Monte Carlo models of the correlated errors for DA and non-DA white dwarfs in the initial–final mass plane. We find the uncertainties in initial–final mass determinations for individual white dwarfs can be significantly asymmetric, but the recovered functional form of the IFMR is grossly unaffected by the correlated errors.

Constraining axion-like particles using the white dwarf initial-final mass relation

Axion-like particles (ALPs), a class of pseudoscalars common to many extensions of the Standard Model, have the capacity to drain energy from the interiors of stars. Consequently, stellar evolution can be used to derive many constraints on ALPs. We study the influence that keV-MeV scale ALPs which interact exclusively with photons can exert on the helium-burning shells of asymptotic giant branch stars, the late-life evolutionary phase of stars with initial masses less than 8M ☉. We establish the sensitivity of the final stellar mass to such energy-loss for ALPs with masses currently permitted by stellar evolution bounds. A semi-empirical constraint on the white dwarf initial-final mass relation (IFMR) derived from observation of double white dwarf binaries is then used to exclude part of a currently unconstrained region of ALP parameter space, the cosmological triangle. The derived constraint relaxes when the ALP decay length becomes shorter than the width of the helium-burning shell. Other potential sources for stellar constraints on ALPs are also discussed.

Massive White Dwarfs in Young Star Clusters

Abstract We have carried out a search for massive white dwarfs (WDs) in the direction of young open star clusters using the Gaia DR2 database. The aim of this survey was (1) to provide robust data for new and previously known high-mass WDs regarding cluster membership, (2) to highlight WDs previously included in the initial final mass relation (IFMR) that are unlikely members of their respective clusters according to Gaia astrometry, and (3) to select an unequivocal WD sample that could then be compared with the host clusters’ turnoff masses. All promising WD candidates in each cluster color–magnitude diagram were followed up with spectroscopy from Gemini in order to determine whether they were indeed WDs and derive their masses, temperatures, and ages. In order to be considered cluster members, white dwarfs were required to (1) have proper motions and parallaxes within 2σ, 3σ, or 4σ of those of their potential parent cluster based on how contaminated the field was in their region of the sky, (2) have a cooling age that was less than the cluster age, and (3) have a mass that was broadly consistent with the IFMR. A number of WDs included in current versions of the IFMR turned out to be nonmembers, and a number of apparent members, based on Gaia’s astrometric data alone, were rejected, as their mass and/or cooling times were incompatible with cluster membership. In this way, we developed a highly selected IFMR sample for high-mass WDs that, surprisingly, contained no precursor masses significantly in excess of ∼ 6 M ⊙.

The White Dwarfs of the Old, Solar-metallicity Open Star Cluster Messier 67: Properties and Progenitors*

Abstract The old, solar-metallicity open cluster Messier 67 has long been considered a lynchpin in the study and understanding of the structure and evolution of solar-type stars. The same is arguably true for stellar remnants; the white dwarf population of M67 provides crucial observational data for understanding and interpreting white dwarf populations and evolution. In this work, we determine the white dwarf masses and derive their progenitor star masses using high signal-to-noise spectroscopy of warm (≳10,000 K) DA white dwarfs in the cluster. From this, we are able to derive each white dwarf’s position on the initial–final mass relation (IFMR), with an average M WD = 0.60 ± 0.01 M ⊙ and progenitor mass M i = 1.52 ± 0.04 M ⊙. These values are fully consistent with recently published linear and piecewise linear fits to the semiempirical IFMR and provide a crucial, precise anchor point for the IFMR for solar-metallicity, low-mass stars. The mean mass of M67 white dwarfs is also consistent with the sharp narrow peak in the local field white dwarf mass distribution, indicating that a majority of recently formed field white dwarfs come from stars with progenitor masses of ≈1.5 M ⊙. Our results enable more precise modeling of the Galactic star formation rate encoded in the field white dwarf mass distribution.