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

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