$\sim$5Å for the WHT and SAAO spectra. Grating \#7 was used with the ALFOSC imaging spectrograph giving a wavelength range 3800–7000Å and a spectral resolution of $\sim$8Å. All the data were reduced using optimal extraction and standard techniques. Several spectra of J0305 were downloaded from the SDSS archive and co-added and re-binned into 4 Å bins.

We modelled the spectra using a grid of LTE models calculated with the [atlas9]{} code (Kurucz 1992) with convective overshooting switched off. Spectra were calculated with the [linfor]{} line-formation code (Lemke 1991). Data for atomic and molecular transitions were compiled from the Kurucz line list. The spectra were fitted with the [fitsb2]{} routine (Napiwotzki et al 2004). The error limits of all fit parameters were determined with a bootstrapping method.

The stellar temperatures were estimated from the hydrogen Balmer lines of the stars (H$\beta$ to H$\epsilon$). No gravity sensitive features are accessible in our low resolution spectra so gravity was fixed at $\log g = 4.0$, which is a typical value for SX Phe and large amplitude $\delta$ Sct stars (eg McNamara 1997).

Apart from the Ca H and K lines, the resolution of our spectra is clearly too low to allow a meaningful 