The spectroscopic variability of T$_{\rm eff}$ and $\log g$ in $\beta$ Cep

Time resolved spectra of $\beta$ Cep yield the following average results: T$_{\rm eff}$ =24000 $\pm$ 250 K, $\log g$ = 3.91 $\pm$ 0.05 and $\xi$ = 8.1 $\pm$ 0.9 km s$^{-1}$. N, O, Ne, Al, Si and S abundances are solar while C, Mg and Fe are slightly under-abundant. Pulsational amplitudes of $\Delta$T$_{\rm eff}$ $\sim$ 700 K and $\Delta$$\log g$ $\sim$ 0.2 dex are found from H$\beta$. The metal lines give similar amplitudes but centred on T$_{\rm eff}$ $\sim$ 25000 K. An upper limit of 1.0 km s$^{-1}$ to the variability of the microturbulence is derived from the Si {\sc iii} triplet at 455 nm. The radial velocity amplitude derived from the core of H$\beta$ is $\sim$ 15% greater than that from the metal lines.