KIC 8553788: A pulsating Algol with an extreme mass ratio

TL;DR

This study analyzes the pulsating Algol-type eclipsing binary KIC 8553788, revealing its extreme mass ratio, detailed pulsational characteristics, and evolutionary status through photometric and spectroscopic data.

Contribution

It provides the first detailed analysis of KIC 8553788's pulsational and physical properties, highlighting its extreme mass ratio and evolutionary implications.

Findings

Primary star: A8 type, 1.6 M_sun, 2 R_sun, 89 pulsation modes.

Secondary star: 0.07 M_sun, 1 R_sun, 4400 K.

System may have the lowest mass ratio in semi-detached binaries.

Abstract

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.