\begin{table}%t3 \par \caption{\label{tab:model}Model parameters for \object{W243}.} \small%\centerline { \begin{tabular}{ll} \hline\hline \noalign{\smallskip} Parameter & Value$^{a}$ \\ \hline &\\[-8pt] $L_{*}$ & $7.3\times10^{5}~(d/4.5~{\rm kpc})^{2}~L_{\odot}$ \\ $R_{*}$ & $376.9~(d/4.5~{\rm kpc})~R_{\odot}$ \\ $R_{2/3}$ & $450.0~(d/4.5~{\rm kpc})~R_{\odot}$ \\ $T_{{\rm eff}}$ & $\sim$8500~K$^{b}$\\ $\dot{M}$ & $6.1$~$\times$ $10^{-7}~(d/4.5~{\rm kpc})^{1.5}~M_{\odot}$~yr$^{-1}$ \\ $V_{\infty}$ & 165~km~s$^{-1}$\\ $v~ \sin i$ & 10~km~s$^{-1}$\\ log~$g$ & $\sim$0.65$^{c}$ \\ H/He & 5\\ N/N$_{\odot}$ & 12.1\\ O/O$_{\odot}$ & 0.11\\ Ca/Ca$_{\odot}$ & 2.49\\ Mg/Mg$_{\odot}$ & 1.34\\ Si/Si$_{\odot}$ & 1.51\\ Fe/Fe$_{\odot}$ & 1.22\\ \hline \end{tabular}} \medskip $^{a}$ Values for $V_{\infty}$, $v~{\rm sin}i$ and H/He are assumed, all others are derived. Values are for a distance of 4.5~kpc \citep{cncg05,crowther06}, with scaling listed where appropriate.\\ $^{b}$~Limits are 8300~$\le$ $T_{{\rm eff}}$~$\le$ 9300~K, favouring a value at the lower end of this range.\\ $^{c}$ Best fit to the higher Paschen-series absorption lines. \end{table}