Spectroscopic Mode Identification in Slowly Pulsating Subdwarf-B Stars

Mode identification is crucial for an asteroseismological study of any significance. Contrarily to spectroscopic techniques, methods such as period-fitting and multi-colour photometry do not provide a full reconstruction of non-radial pulsations. We present a new method of spectroscopic mode identification and test it on time-series of synthetic spectra appropriate for pulsating subdwarf-B stars. We then apply it to the newly discovered slowly pulsating subdwarf-B star HD 4539.