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 _ { 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 ) .