* Astronomy

Title: KIC 8262223: A Post-Mass Transfer Eclipsing Binary Consisting of a Delta Scuti Pulsator and a Helium White Dwarf Precursor
Author: Zhao Guo, Douglas R. Gies, Rachel A. Matson, Antonio García Hernández, Zhanwen Han, Xuefei Chen

KIC~8262223 is an eclipsing binary with a short orbital period (P=1.61 d). The Kepler light curves are of Algol-type and display deep and partial eclipses, ellipsoidal variations, and pulsations of Delta Scuti type. We analysed the Kepler photometric data, complemented by phase-resolved spectra from the R-C Spectrograph on the 4-meter Mayall telescope at Kitt Peak National Observatory and determined the fundamental parameters of this system. The low mass and oversized secondary (M2=0.20 solar masses, R2=1.31 solar radii) 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 delta 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 the system can be understood as the result of non-conservative binary evolution similar to that 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 (M1=1.94 solar masses, R1=1.67 solar radii) but the predicted unstable modes associated with these models differ somewhat from those observed. This work presents a preliminary asteroseismic analysis of the abnormal Delta Scuti pulsators, and we discuss the need for better theoretical understanding of such pulsating mass gaining stars.

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