EL Canum Venaticorum Star

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EL Canum Venaticorum stars are a class of eclipsing stars . The binary stars consist of an AF main sequence star and a star with a mass of less than 0.35 solar masses on the evolutionary path of post-AGB stars , which further transform into a white dwarf .

Development and importance

White dwarfs with a mass of less than 0.35 solar masses can only arise in interacting binary stars due to the age of the universe of 13.8 billion years , since the stay of red dwarfs on the main sequence exceeds the age of the cosmos. The EL-CVn double stars arise in a common envelope phase in which the later white dwarf develops into a red giant and, due to its expansion, carries out an unstable mass exchange on its companion. The companion gains mass and becomes a main sequence star with the spectral class A or F. This corresponds to a mass of 1.05 to 2.9 solar masses. After the common shell phase, the former red giant no longer has enough mass to start a helium burn and the exposed former core consists almost exclusively of helium with traces of metals . The future white dwarf follows the evolution of post-AGB stars and moves quickly to the left in the Hertzsprung-Russell diagram to higher temperatures as the star's radius decreases.

While hiking through the HR chart, the former red giant crosses the instability strip and begins to pulse . With the help of asteroseismology and the eclipsing light change it is possible to study the development and structure of these stars on the way to a white dwarf in detail. White dwarfs with extremely low mass also appear as companions with millisecond pulsars , X-ray pulsars, and AM Canum Venaticorum stars . According to theoretical models, EL-CVn stars could be candidates for a late thermal pulse in which the white dwarf would drop another 0.1 solar masses.

Examples

  • EL CVn
  • 1SWASP J024743.37−251549.2
  • TYC 1755-509-1
  • HD 127051

literature

  • Chen Xuefei, Maxted PFL, Li Jiao, Han Zhanwen: The Formation of EL CVn-type Binaries . In: Astrophysics. Solar and Stellar Astrophysics . 2016, arxiv : 1604.01956v2 .
  • PFL Maxted, AM Serenelli, TR Marsh, S. Catalán, DP Mahtani, VS Dhillon: WASP 1628 + 10 - an EL CVn-type binary with a very-low-mass stripped-red-giant star and multi-periodic pulsations . In: Astrophysics. Solar and Stellar Astrophysics . 2014, arxiv : 1407.5415v2 .
  • PFL Maxted t al .: EL CVn-type binaries - Discovery of 17 helium white dwarf precursors in bright eclipsing binary star systems . In: Astrophysics. Solar and Stellar Astrophysics . 2013, arxiv : 1310.4863v1 .