Asteroseismology of Kepler Algol type oscillating eclipsing binaries

Context. This research paper contains light curve modelling, spectroscopy and detailed asteroseismic studies for four out of five in total semidetached eclipsing binaries with a delta Scuti component, that have been detected to date through Kepler mission, namely KIC 06669809, KIC 10581918, KIC 10619109 and KIC 11175495. Aims. The goal is to study the pulsational characteristics of the oscillating stars of the systems as well as to estimate their absolute parameters and enrich the so far poor sample of this kind of systems. Methods. Ground based spectroscopic observations provide the means to estimate the spectral types of the primary components and to model the light curves with higher certainty. The photometric data are analysed using eclipsing binary modeling techniques, while Fourier analysis is applied on their residuals in order to reveal the pulsation frequency modes. Results. The results of analyses show that the primaries are pulsating stars of delta Scuti type and that all systems belong to the group of Algol type binaries with an oscillating star, namely oEA stars. The primaries of KIC 06669809, KIC 10581918, and KIC 10619109 pulsate in three, two, and five frequencies, respectively and in more than 200 other detected as combinations. The delta Scuti star of KIC 11175495 is the youngest and the fastest pulsator in binary systems that has ever been found and it oscillates in three main non radial frequencies, while other 153 are also found as depended ones. Moreover, a comparison of their properties with other systems of the same type as well as with theoretical models of pulsating stars are also presented and discussed.Comment: 22 pages, 29 figures, accepted for publication in A&

KIC 8553788: A pulsating Algol with an extreme mass ratio

The present paper focuses on the eclipsing binary KIC 8553788 which belongs to two different types of binary systems regarding its physical properties. In particular, it is one of the 71 oscillating stars of Algol type that have been discovered so far and one of the six that have been published based on high cadence data of the Kepler mission. In addition, it is one of the four semi-detached binaries of the group of R CMa type systems, while its pulsating component has the fourth fastest frequency among the delta Scuti stars-members of semi-detached binaries. Detailed light curves, spectroscopic and pulsation analyses are presented, while possible explanation scenarios for the evolution of the system involving past mass transfer, mass loss and/or angular momentum loss due to the presence of a tertiary component are discussed. The goal of the study is to extract the pulsational characteristics of the oscillating star of the system, to estimate the absolute parameters of its components and to provide possible explanation for its extreme evolutionary status. The results show that the primary component of the system is of A8 spectral type, has a mass of 1.6 M_sun, and a radius of 2 R_sun. It is a relatively fast pulsator that oscillates in 89 frequency modes with the dominant one to be 58.26 c/d. The secondary component has a mass of only 0.07 M_sun, a radius of 1 R_sun, and a temperature of 4400 K. KIC 8553788 according to its geometrical configuration and its pulsational properties belongs to the group of the oscillating stars of Algol type, while according to its very low mass ratio and its relatively short orbital period belongs also to the group of R CMa stars. If confirmed by radial velocity data of the secondary component, the system would have the lowest mass ratio that has ever been found in semi-detached systems and it can be considered as one of the most extreme cases.Comment: 13 pages, 17 figures. Accepted for publication in Astronomy & Astrophysic