A Photometric, Spectroscopic, and Apsidal Motion Analysis of the F-type Eclipsing Binary BW Aquarii from K2 Campaign 3

TL;DR

This study combines photometric and spectroscopic data to analyze the eclipsing binary BW Aquarii, measuring its stellar and orbital parameters, and testing stellar evolution models against observed properties.

Contribution

It provides a comprehensive analysis of BW Aquarii using K2 photometry and high-resolution spectroscopy, including updated apsidal motion and atmospheric parameters, highlighting discrepancies with models.

Findings

Both stars are late F-type with precise mass and radius measurements.

Models fail to simultaneously match observed properties of both stars at a single age.

The system exhibits slow apsidal motion, providing constraints on stellar interior models.

Abstract

Eclipsing binaries are important tools for studying stellar evolution and stellar interiors. Their accurate fundamental parameters are used to test evolutionary models, and systems showing apsidal motion can also be used to test the model's internal structure predictions. For this purpose, we present a photometric and spectroscopic analysis of the eclipsing binary BW Aquarii, an evolved F-type binary with slow apsidal motion. We model the K2 C3 light curve using the Eclipsing Light Curve code to determine several orbital and stellar parameters, as well as measure the eclipse times to determine updated apsidal motion parameters for the system. Furthermore, we obtain high-resolution spectra of BW Aqr using the CHIRON echelle spectrograph on the CTIO 1.5m for radial velocity analysis. We then reconstruct the spectra of each component using Doppler tomography in order to determine the atmospheric parameters. We find that both components of BW Aqr are late F-type stars with M1 = 1.365 +/- 0.008 Msun, M2 = 1.483 +/- 0.009 Msun, and R1 = 1.782 +/- 0.021 Rsun, R2 = 2.053 +/- 0.020 Rsun. We then compare these results to the predictions of several stellar evolution models, finding that the models cannot reproduce the observed properties of both components at the same age.