The Formation Rate and Mass and Luminosity Functions of DA White Dwarfs from the Palomar Green Survey

By J. Liebert, Pierre Bergeron, J. Holberg. 2004

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Spectrophotometric observations at high signal-to-noise ratio were obtained of a complete sample of 348 DA white dwarfs from the Palomar Green (PG) Survey. Fits of observed Balmer lines to synthetic spectra calculated from pure-hydrogen model atmospheres were used to obtain robust values of Teff, log g, masses, radii, and cooling ages. The luminosity function of the sample, weighted by 1/Vmax, was obtained and compared with other determinations. Incompleteness of the sample due to selection by photographic mu - mb color and magnitude limits was found to be a serious problem, and an attempt is made to correct for this. The mass distribution of the white dwarfs is derived, after important corrections for the radii of the white dwarfs in this magnitude-limited survey and for the cooling time scales. This distribution has (1) a "peak" component centered near 0.6 M⊙, (2) a low-mass component centered near 0.4 M⊙, and (3) a high-mass component above about 0.8 M⊙. The formation rate of DA white dwarfs from the PG is estimated to be 0.6 × 10-12 pc-3 yr-1. Of these, 75% are from the peak component, 10% from the low-mass component, and 15% from the high-mass component. The low-mass component requires binary evolution for 100% of the objects, with a degenerate companion likely in the majority of cases. Comparison with predictions from a theoretical study of the white dwarf formation rate for single stars indicates that ≥80% of the high-mass component requires a different origin, presumably mergers of lower mass double degenerate stars. The need for a binary channel may not be as great for the massive, very hot white dwarfs found in the EUV all-sky surveys. In an Appendix, we even suggest that an enhanced density of the massive white dwarfs at lower Galactic latitudes might be due to some of them being the progeny of B stars in Gould's Belt. In order to estimate the recent formation rate of all white dwarfs in the local Galactic disk, corrections for incompleteness of the PG, addition of the DB-DO white dwarfs, and allowance for stars hidden by luminous binary companions had to be applied to enhance the rate. An overall formation rate of white dwarfs recently in the local Galactic disk of (1 ± 0.25) × 10-12 pc-3 yr-1 is obtained. Admittedly, the systematic errors in this estimate are difficult to quantify. Two recent studies of samples of nearby Galactic planetary nebulae lead to estimates around twice as high. Difficulties in reconciling these determinations are discussed.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/b4128c0f5a51ab3cce72f1cd300f0c0a7288a3f6

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The Progenitors of Type Ia Supernovae (2012, background): “It has been found that∼10% of WDs have magnetic fields stronger than 1 MG (Liebert et al., 2003, 2005; Wickramasinghe and Ferrario, 2005).”
The helium star donor channel for the progenitors of Type Ia supernovae (2009, background): “In addition, it is suggested that about 10% of WDs have magnetic fields higher than 1 MG (Liebert et al. 2003, 2005).”
Evolutionary and pulsational properties of white dwarf stars (2010, background): “29 3.4 The formation of low-mass white dwarfs About 10% of the white dwarf population is characterized by stellar masses below 0.4M⊙ (Liebert et al. 2005).”
The frequency of planetary debris around young white dwarfs (2014, methodology): “1 resembles closely that of larger well-studied samples (Finley et al. 1997; Liebert et al. 2005; Giammichele et al. 2012), displaying besid s the dominant population around a mean mass of 0.6M⊙ two additional peaks near≈0.4 M⊙ and≈0.8 M⊙.”
AN IMPROVED SPECTROSCOPIC ANALYSIS OF DA WHITE DWARFS FROM THE SLOAN DIGITAL SKY SURVEY DATA RELEASE 4 (2011, methodology): “1 of Liebert et al. 2005).”
The initial–final mass relationship of white dwarfs revisited: effect on the luminosity function and mass distribution (2008, methodology): “In this work, we use the atmospheric parameters determined by Liebert et al. (2005a), an age of 237±12 Myr and solar metallicity.”
A COMPREHENSIVE SPECTROSCOPIC ANALYSIS OF DB WHITE DWARFS (2011, methodology): “Here we rely on the procedure developed by Liebert et al. (2005), where the fluxed spectrum is first fitted with model spectra, multiplied by a high order polynomial (up to λ5), in order to account for any residual error in the flux calibration.”
The Initial-Final Mass Relation: Direct Constraints at the Low-Mass End (2007, background): “A slightly less massive star such as the progenitor of Sirius B (5.06 M⊙ – Liebert et al. 2005) has lost 80% of its mass.”
Evolution of asymptotic giant branch stars. I. Updated synthetic TP-AGB models and their basic calibration (2007, methodology): “…et al. 2001), M 37 (open squares, Kalirai et al. 2005), Praesepe (crosses, Claver et al. 2001, and Dobbie et al. 2006), M 35 (full squares, Williams et al. 2004), Sirius B (star, Liebert et al. 2005a), Pleiades (full triangle, Dobbie et al. 2006), and NGC 2516 (open circles, Ferrario et al. 2005).”
The Sloan Digital Sky Survey View of the Palomar-Green Bright Quasar Survey (2005, result): “This finding is confirmed independently by a comparison of the sample of DAwhite dwarfs from the PG to samples selected in other wavebands, which shows color incompleteness beginning at U B ¼ 1 and increasing toward redder colors (Liebert et al. 2005; J. Liebert 2004, private communication).”
REDDENING AND EXTINCTION TOWARD THE GALACTIC BULGE FROM OGLE-III: THE INNER MILKY WAY'S RV ∼ 2.5 EXTINCTION CURVE (2012, background): “Moreover, 10% of field white dwarfs have masses lower than the helium-ignition limit (Liebert et al. 2005), some of which are not in binaries (Brown et al. 2011).”