Evolutionary and pulsational properties of white dwarf stars

Abstract

White dwarf stars are the final evolutionary stage of the vast majority of stars, including our Sun. Since the coolest white dwarfs are very old objects, the present population of white dwarfs contains a wealth of information on the evolution of stars from birth to death, and on the star formation rate throughout the history of our Galaxy. Thus, the study of white dwarfs has potential applications to different fields of astrophysics. In particular, white dwarfs can be used as independent reliable cosmic clocks, and can also provide valuable information about the fundamental parameters of a wide variety of stellar populations, like our Galaxy and open and globular clusters. In addition, the high densities and temperatures characterizing white dwarfs allow to use these stars as cosmic laboratories for studying physical processes under extreme conditions that cannot be achieved in terrestrial laboratories. Last but not least, since many white dwarf stars undergo pulsational instabilities, the study of their properties constitutes a powerful tool for applications beyond stellar astrophysics. In particular, white dwarfs can be used to constrain fundamental properties of elementary particles such as axions and neutrinos, and to study problems related to the variation of fundamental constants.These potential applications of white dwarfs have led to a renewed interest in the calculation of very detailed evolutionary and pulsational models for these stars. In this work, we review the essentials of the physics of white dwarf stars. We enumerate the reasons that make these stars excellent chronometers and we describe why white dwarfs provide tools for a wide variety of applications. Special emphasis is placed on the physical processes that lead to the formation of white dwarfs as well as on the different energy sources and processes responsible for chemical abundance changes that occur along their evolution. Moreover, in the course of their lives, white dwarfs cross different pulsational instability strips. The existence of these instability strips provides astronomers with an unique opportunity to peer into their internal structure that would otherwise remain hidden from observers. We will show that this allows to measure with unprecedented precision the stellar masses and to infer their envelope thicknesses, to probe the core chemical stratification, and to detect rotation rates and magnetic fields. Consequently, in this work, we also review the pulsational properties of white dwarfs and the most recent applications of white dwarf asteroseismology.

Accelerated post-AGB evolution, initial-final mass relations, and the star-formation history of the Galactic bulge

“…This has only recently become possible, using asteroseismology on pulsating central stars. Althaus et al (2010) lists eight such central stars of PNe with measured masses. They are reproduced in Table 2.…”

“…We extend the mass range covered by the Blöcker models by using the PN central stars with asteroseismological masses, which reach temperatures of 130 kK for M c = 0.53 M (Althaus et al 2010). (The lower mass models in Schönberner (1983) do not reach such high temperatures.)…”

New evolutionary sequences for extremely low-mass white dwarfs

“…In addition, they are used to place constraints on properties of elementary particles, such as axions (Isern et al 1992(Isern et al , 2008Córsico et al 2012a,b) and neutrinos (Winget et al 2004), or on alternative theories of gravitation (García-Berro et al 1995. These and other potential applications of white dwarfs require a detailed and precise knowledge of the main physical processes that control their evolution (see Fontaine & Brassard 2008;Kepler 2008, andAlthaus et al 2010a, for a review).…”

New phase diagrams for dense carbon-oxygen mixtures and white dwarf evolution

“…White dwarf stars constitute the most common end-point of stellar evolution -see, for instance, Althaus et al (2010a) for a recent review -and as such are valuable in constraining several properties of a wide variety of stellar populations including globular and open clusters (Von Hippel & Gilmore 2000;Hansen et al 2007;Winget et al 2009;García-Berro et al 2010). Additionally, they can be used to place constraints on exotic elementary particles (Isern et al 1992;Córsico et al 2001;Isern et al 2008) or on alternative theories of gravitation (García-Berro et al 1995;Benvenuto et al 2004;García-Berro et al 2011).…”