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KIC 8262223: A Post-mass Transfer Eclipsing Binary Consisting of a Delta Scuti Pulsator and a Helium White Dwarf Precursor

Z. Guo, D. R. Gies, R. A. Matson, A. GarcŪa HernŠndez, Z. Han, X. Chen

Abstract

KIC 8262223 is an eclipsing binary with a short orbital period (P = 1.61 day). The Kepler light curves are of Algol-type and display deep and partial eclipses, ellipsoidal variations, and pulsations of δ Scuti type. We analyzed the Kepler photometric data, complemented by phase-resolved spectra from the R-C Spectrograph on the 4 meter Mayall telescope at the Kitt Peak National Observatory and determined the fundamental parameters of this system. The low-mass and oversized secondary (M2 = 0.20 M, R2 = 1.31R ) is the remnant of the donor star that transferred most of its mass to the gainer, and now the primary star. The current primary star is thus not a normal δ Scuti star but the result of mass accretion from a lower mass progenitor. We discuss the possible evolutionary history and demonstrate with the MESA evolution code that this system and several other systems discussed in prior literature can be understood as the result of non-conservative binary evolution for the formation of EL CVn-type binaries. The pulsations of the primary star can be explained as radial and non-radial pressure modes. The equilibrium models from single star evolutionary tracks can match the observed mass and radius (M2 = 1.94 M, R2 = 1.67R ) but the predicted unstable modes associated with these models differ somewhat from those observed. We discuss the need for better theoretical understanding of such post-mass transfer δ Scuti pulsators.

Keywords
binaries: eclipsing; stars: evolution; stars: oscillations: including pulsations; stars: variables: delta Scuti; white dwarfs; Astrophysics - Solar and Stellar Astrophysics

Astronomy and Astrophysics
Volume 606, Article Number A75
2017 October

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Instituto de Astrof√≠sica e Ci√™ncias do Espa√ßo Universidade do Porto Faculdade de Ciências da Universidade de Lisboa Funda√ß√£o para a Ci√™ncia e a Tecnologia
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