Evolutionary and pulsational properties of white dwarf stars

L. G. ALTHAUS; A. H. CÓRSICO; J. ISERN; E. GARCÍA-BERRO

ASTRONOMY AND ASTROPHYSICS REVIEW

SPRINGER

Año: 2010 vol. 18 p. 471 - 566

0935-4956

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  precise information on the evolution  of stars from birth to death, and on the star formation rate throughout the history of our own Galaxy. The study of  white dwarfs has thus potential applications to different fields  of astrophysics. In particular, the  use of white dwarfs  as  independent   reliable  cosmic  clocks  provides  valuable constraints to  fundamental parameters for  a wide variety  of stellar populations,  like our  Galaxy  and open  and  globular clusters.   In addition, the high densities  and temperatures that characterize white dwarfs turn  these objects into cosmic laboratories  to study numerous 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 undoubtedly led to a renewed interest in the  computation of very detailed evolutionary and pulsational  models for  these stars.   In  this work,  we review  the essentials of the physics of  white dwarf stars in order to understand the reasons that make these stars excellent chronometers and potentialtools 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  to the different energy sources  and processes responsible for chemical  abundance changes that occur along  their evolution.  As it is  well known, in  the course of  their lives, white  dwarfs crossdistinct  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.   This  allows   us  to  measure  with  unprecedented precision  the stellar masses  and to  infer envelope  thicknesses, toprobe the  core chemical stratification, and to  detect rotation rates and magnetic  fields.  In  this work, we  also review  the pulsational properties of white  dwarfs and the most recent  applications of white dwarf asteroseismology.