Absolute dimensions and evolutionary status of the semi-detached Algol W Ursae Minoris

TL;DR

This study precisely determines the fundamental parameters of the semi-detached Algol W UMi binary system through spectroscopic and photometric data, revealing its evolutionary status and mass transfer history.

Contribution

It provides a detailed set of physical parameters for W UMi and compares them with stellar models to understand its evolutionary stage, especially the mass transfer process.

Findings

Primary star is on the main sequence.

Secondary star is significantly evolved.

Mass transfer has altered the original mass hierarchy.

Abstract

Double-lined eclipsing binaries allow accurate and direct determination of fundamental parameters such as mass and radius for each component, and they provide important constraints on the stellar structure and evolution models. In this study, we aim to determine a unique set of binary parameters for the Algol system W UMi and to examine its evolutionary status. New high-resolution time-series spectroscopic observations were carried out during 14 nights from April 2008 to March 2011, and a total of 37 spectra were obtained using the Bohyunsan Optical Echelle Spectrograph. We measured the radial velocities (RVs) for both components, and the effective temperature of the primary star was found to be $T_{\rm eff,1}$ = 9310 $\pm$ 90 K by a comparison of the observed spectra and the Kurucz models. The physical parameters of W UMi were derived by an analysis of our RV data together with the multi-band light curves of Devinney et al. (1970). The individual masses, radii, and luminosities of both components are $M_1$ = 3.68 $\pm$ 0.10 M$_\odot$ and $M_2$ = 1.47 $\pm$ 0.04 M$_\odot$, $R_1$ = 3.88 $\pm$ 0.03 R$_\odot$ and $R_2$ = 3.13 $\pm$ 0.03 R$_\odot$, and $L_1$ = 102 $\pm$ 1 L$_\odot$ and $L_2$ = 7.3 $\pm$ 0.1 L$_\odot$, respectively. A comparison of these parameters with theoretical stellar models showed that the primary component lies in the main-sequence band, while the less massive secondary is noticeably evolved. The results indicate that the initially more massive star became the present secondary by losing most of its own mass via mass transfer to the companion (present primary).