The Initial‐Final Mass Relation: Direct Constraints at the Low‐Mass End

Abstract

The initial-final mass relation represents a mapping between the mass of a white dwarf remnant and the mass that the hydrogen-burning main-sequence star that created it once had. The empirical relation thus far has been constrained using a sample of $40 stars in young open clusters, ranging in initial mass from $2.75 to 7 M , and shows a general trend that connects higher mass main-sequence stars with higher mass white dwarfs. In this paper, we present CFHT CFH12K photometric and Keck LRIS multiobject spectroscopic observations of a sample of 22 white dwarfs in two older open clusters, NGC 7789 (t ¼ 1:4 Gyr) and NGC 6819 (t ¼ 2:5 Gyr). We measure masses for the highest signalto-noise ratio spectra by fitting the Balmer lines to atmosphere models and place the first direct constraints on the lowmass end of the initial-final mass relation. Our results indicate that the observed general trend at higher masses continues down to low masses, with M initial ¼ 1:6 M main-sequence stars forming M Bnal ¼ 0:54 M white dwarfs. When added to our new data from the very old cluster NGC 6791, the relation is extended down to M initial ¼ 1:16 M (corresponding to M Bnal ¼ 0:53 M ). This extension of the relation represents a fourfold increase in the total number of hydrogen-burning stars for which the integrated mass loss can now be calculated from empirical data, assuming a Salpeter initial mass function. The new leverage at the low-mass end is used to derive a purely empirical initial-final mass relation. The sample of white dwarfs in these clusters also shows several interesting systems that we discuss further: a DB (helium) white dwarf, a magnetic white dwarf, a DAB (mixed hydrogen/helium atmosphere or a double degenerate DA+DB) white dwarf(s), and two possible equal-mass DA double degenerate binary systems.

The age of the Milky Way inner halo

“…Accepted for Publication in Nature on March 14 th 2012 14 formed from heavier progenitors 11,20,21 . The well--measured age of Messier 4 provides an anchor to convert the mass difference to an age difference.…”

Testing the Initial–Final Mass Relationship of White Dwarfs

“…We include the recent results obtained by Kalirai et al (2007b) based on spectroscopic observations of white dwarfs in these clusters. These results, as well as those we have obtained using common proper motion pairs constitute the first constraints on the low-mass end of the initial-final mass relationship.…”

“…The white dwarf population of this cluster has relatively low masses (< 0.47M ⊙ ), so the majority of white dwarfs belonging to this cluster could have a He-core. Although it has been elucidated that He-core white dwarfs could be formed also by single-evolution (Kilic et al 2007), we prefer not to take these white dwarfs into account, and only consider the two confirmed cluster members with masses above this value and compatible with a C/O-core composition, as it was done in Kalirai et al (2007b). The white dwarf population of NGC 7789 and NGC 6819 were also studied recently by Kalirai et al (2007b).…”

Asymptotic Giant Branch Evolution and the Initial-Final Mass Relation of Single CO White Dwarfs

“…The data show a clear positive correlation between the white dwarf mass and the mass of the stellar progenitor. Recently the IFMR has been extended into the low-mass range (M i < 2.5 M ) thanks to inclusion of white dwarfs members of common proper motion pairs (CPMP; Catalán et al 2008), or detected in old open clusters (Kalirai et al 2008). Deriving the semi-empirical IFMR requires the intensive use of theoretical models, i.e.…”

“…assessment of cluster's age and metallicity, amount of convective overshooting, thickness of the white dwarf H/He layers, The IFMR of Single CO White Dwarfs 37 Figure 1. Semi-empirical IFMR based on the compilation by Ferrario et al (2005), Kalirai et al (2008), andCatalán et al (2008). Solid lines are linear fits provided by various authors quoted in the plot.…”