TWO MASSIVE WHITE DWARFS FROM NGC 2323 AND THE INITIAL–FINAL MASS RELATION FOR PROGENITORS OF 4–6.5 M_⊙*

Abstract

We observed a sample of 10 white dwarf candidates in the rich open cluster NGC 2323 (M50) with the Keck LowResolution Imaging Spectrometer. The spectroscopy shows eight to be DA white dwarfs, with six of these having high signal-to-noise ratio appropriate for our analysis. Two of these white dwarfs are consistent with singly evolved cluster membership, and both are high mass ∼1.07 M e , and give equivalent progenitor masses of 4.69 M e . To supplement these new high-mass white dwarfs and analyze the initial-final mass relation (IFMR), we also looked at 30 white dwarfs from publicly available data that are mostly all high-mass ( 0.9 M e ). These original published data exhibited significant scatter, and to test if this scatter is true or simply the result of systematics, we have uniformly analyzed the white dwarf spectra and have adopted thorough photometric techniques to derive uniform cluster parameters for their parent clusters. The resulting IFMR scatter is significantly reduced, arguing that mass-loss rates are not stochastic in nature and that within the ranges of metallicity and mass analyzed in this work mass loss is not highly sensitive to variations in metallicity. Lastly, when adopting cluster ages based on Y 2 isochrones, the slope of the high-mass IFMR remains steep and consistent with that found from intermediate-mass white dwarfs, giving a linear IFMR from progenitor masses between 3 and 6.5 M e . In contrast, when adopting the slightly younger cluster ages based on PARSEC isochrones, the high-mass IFMR has a moderate turnover near an initial mass of 4 M e .

Mass loss of stars on the asymptotic giant branch

“…Data have been obtained studying WDs in, e.g., wide binaries ) and in clusters (Kalirai et al 2014;Cummings et al 2015, and references therein). Cummings et al (2016) found a tight relation between the main sequence mass M MS and the final mass M f , M f = 0.154 M MS + 0.261, up to ≈ 4 M , beyond which the relation appears less steep reaching M f ≈ 1.2 M at M MS = 8 M , Fig. 11.…”

“…There is good evidence that AGB stars with masses up to 6-8 M manage to end their AGB evolution with a core mass below the Chandrasekhar limit of about 1.4 M (Cummings et al 2016). Most of the mass loss occurs on the AGB, except for the lower-mass stars where mass loss on the RGB is substantial in a relative sense, of the order 0.25 M in total (McDonald et al 2009(McDonald et al , 2011Lebzelter and Wood 2011).…”

“…3.2. At least, from the similarity of the M WD -distributions in open clusters of different metallicity, one may conclude that the total amount of mass lost does not depend (strongly) on the metallicity (Cummings et al 2016). Detecting a weak metallicity effect may be a challenge for observational studies, due to the contamination with dependences on other stellar properties, combined with the scatter in the mass-loss-rate estimates.…”

Progress and Application of The Initial-Final Mass Relation

“…With the advent of wide-field imagers and multi-object spectrographs on larger telescopes over the past 15 years, there has been an explosion of new white dwarf data. Namely in NGC 2099 (Kalirai et al 2005), Praesepe (Dobbie et al 2006a;Casewell et al 2009), NGC 6791 (Kalirai et al 2007), NGC 6819 and NGC 7789 (Kalirai et al 2008), NGC 2287 and NGC 3532 (Dobbie et al 2009), NGC 2618 (Williams et al 2004;, Kalirai et al (2014) and Cummings et al (2015;2016a;2016b), which analyzed newly discovered white dwarfs and uniformly analyzed previous data publicly available. Green points show the Pleiades white dwarfs connected only kinematically to the cluster (Dobbie et al 2006b).…”

“…To begin to address both of these limitations, Cummings et al (2015;2016a;2016b) have searched for new massive white dwarfs and have done detailed self-consistent analysis of both the white dwarf spectroscopy and open cluster photometry. For the wellstudied brightest white dwarfs, however, the parameters from the identical spectroscopic analysis in Gianninas et al (2011) Cummings (2009) and the automated fitting techniques of Bergeron et al (1992).…”