The white dwarf luminosity function

Abstract

White dwarfs are the final remnants of low-and intermediate-mass stars. Their evolution is essentially a cooling process that lasts for ∼ 10 Gyr. Their observed properties provide information about the history of the Galaxy, its dark matter content and a host of other interesting astrophysical problems. Examples of these include an independent determination of the past history of the local star formation rate, identification of the objects responsible for the reported microlensing events, constraints on the rate of change of the gravitational constant, and upper limits to the mass of weakly interacting massive particles. To carry on these tasks the essential observational tools are the luminosity and mass functions of white dwarfs, whereas the theoretical tools are the evolutionary sequences of white dwarf progenitors, and the corresponding white dwarf cooling sequences. In particular, the observed white dwarf luminosity function is the key manifestation of the white dwarf cooling theory, although other relevant ingredients are needed to compare theory and observations. In this review we summarize the recent attempts to empirically determine the white dwarf luminosity function for the different Galactic populations. We also discuss the biases that may affect its interpretation. Finally, we elaborate on the theoretical ingredients needed to model the white dwarf luminosity function, paying special attention to the remaining uncertainties, and we comment on some applications of the white dwarf cooling theory. Astrophysical problems for which white dwarf stars Email addresses: enrique.garcia-berro@upc.edu (Enrique García-Berro), terry.oswalt@erau.edu (Terry D. Oswalt) Preprint submitted to New Astronomy ReviewsAugust 10, 2016 may provide useful leverage in the near future are also discussed.

A white dwarf catalogue from Gaia-DR2 and the Virtual Observatory

“…Much of this information can be recovered by analysing the white dwarf luminosity function, which is defined as the number of white dwarfs per bolometric magnitude unit and cubic parsec. First derived by Weidemann (1968) four decades ago, the white dwarf luminosity function has been used since then as a valuable tool to understand the nature and the history of the different components of our Galaxy (see García-Berro & Oswalt 2016, for a comprehensive and recent review). For instance, the white dwarf luminosity function has been used in the study of both the thin and thick discs (Winget et al 1987;Garcia-Berro et al 1988;García-Berro et al 1999;Torres et al 2002;Rowell 2013), the halo (Mochkovitch et al 1990;Isern et al 1998;García-Berro et al 2004;van Oirschot et al 2014) and more recently, the bulge (Calamida et al 2014;Torres et al 2018).…”

A Deep Proper Motion Catalog Within the Sloan Digital Sky Survey Footprint. Ii. The White Dwarf Luminosity Function

“…White dwarfs (WDs) are the endpoint of stellar evolution for stars lighter than 8-10M ☉ (Williams et al 2009;García-Berro & Oswalt 2016), or greater than 97% of Galactic stars. As the direct remnants of earlier star formation, WDs are an important tool in studying the evolution of our Galaxy.…”

White Dwarf Stars

“…The radius of an average white dwarf star is of the same order of the Earth's radius, which implies that they have small surface area, resulting in very large cooling times; it takes approximately 10 10 years for the effective temperature of a normal mass white dwarf to decrease from 100 000 K to near 5 000 K. Consequently, the cool normal mass ones are still visible and among the oldest objects in the Galaxy. 4 Therefore, studying white dwarfs is extremely important to comprehend the processes of stellar formation and evolution in the Milky Way.…”