All Figures

$\begin{figure} \par\includegraphics[width=7.3cm,clip]{7115fig1} \end{figure}$ Figure 1: Evolutionary track of the mass gainer in our $16~M_\odot+ 15~M_\odot$ early Case B binary model (5 d initial orbital period) in the HR diagram (solid line), from the zero age main sequence up to core carbon exhaustion. The main evolutionary phases are labeled by numbers (see legend). The dashed line shows the evolutionary track of a very rapidly rotating ( $\varv_{~{\rm init}}/\varv_{~{\rm K}}=0.9$ ) $24~M_\odot$ single star. Both stars have SMC metallicity, and undergo quasi-chemically homogeneous evolution (see text).
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{7115fig2} \end{figure}$ Figure 2: Upper panel: equatorial rotation velocity (dashed line) and critical rotation velocity (solid line) of the mass gainer of the computed $16~M_\odot+ 15~M_\odot$ early Case B binary sequence, as function of time, from the zero-age main sequence until core carbon exhaustion. Lower panel: mass loss rate of the same stellar model, as function of time. The numbered evolutionary stages correspond to those given in Fig. 1 and Table 1.
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{7115fig3} \end{figure}$ Figure 3: Evolution of the internal structure of the mass gainer of the computed $16~M_\odot+ 15~M_\odot$ early Case B binary sequence, as function of time, from the zero-age main sequence to core carbon exhaustion. The time axis is logarithmic, with the time of core collapse as zero point. Convective layers are hatched. Semiconvective layers are marked by dots (red dots in the electronic version). Gray (blue) shading indicates nuclear energy generation (color bar to the right of the figure). The topmost solid line denotes the surface of the star.
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{7115fig4} \end{figure}$ Figure 4: Evolution of the internal structure of a single star model with initial mass of 24 $M_{\odot }$ and initial rotation close to Keplerian ( $\varv_{~{\rm init}}/\varv_{~{\rm K}}=0.9$ ). The evolution is shown from the zero-age main sequence to the end of O burning. Convective layers are hatched. Semi-convective layers are marked by dots (red dots in the electronic version). The gray (blue) shading gives nuclear energy generation rates in log scale, as indicated on the right side. The topmost solid line denotes the surface of the star.
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In the text