Astrophys. J., 676, 594-609 (2008/March-3)
The initial-final mass relation: direct constraints at the low-mass end.
KALIRAI J.S., HANSEN B.M.S., KELSON D.D., REITZEL D.B., RICH R.M. and RICHER H.B.
Abstract (from CDS):
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=1.4 Gyr) and NGC 6819 (t=2.5 Gyr). We measure masses for the highest signal-to-noise ratio spectra by fitting the Balmer lines to atmosphere models and place the first direct constraints on the low-mass end of the initial-final mass relation. Our results indicate that the observed general trend at higher masses continues down to low masses, with Minitial=1.6 M☉main-sequence stars forming Mfinal=0.54 M☉ white dwarfs. When added to our new data from the very old cluster NGC 6791, the relation is extended down to Minitial=1.16 M☉(corresponding to Mfinal=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.
open clusters and associations: individual (NGC 6819) - open clusters and associations: individual (NGC 7789) - Stars: Evolution - Techniques: Photometric - Techniques: Spectroscopic - Stars: White Dwarfs
Table 2: Cl* NGC 7789 KHK NN (Nos 1-15). Cl* NGC 6819 KHK NN (Nos 1-13).
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