2011ApJ...734...59G

We first present the results of follow-up photometric observations of the He-rich hot B subdwarf LS IV-14°116, which confirm the presence of multiperiodic luminosity variations in the light curve of this star. Rather surprisingly, no other follow-up observations of this kind seem to have been published after the initial suggestion in 2005 that LS IV-14°116 could be a pulsating star of a new kind. We were able to extract from our data at least six significant periodicities ranging from 1954 s to 5084 s, including the two oscillations uncovered previously. We also present the results of an analysis combining a high signal-to-noise optical spectrum of LS IV-14°116 with recently developed non-local thermodynamic equilibrium model atmospheres and synthetic spectra. Our best estimates of the atmospheric parameters of this star are T_eff = 34950±250 K, log g = 5.93±0.04, and log N(He)/N(H) = -0.62±0.03 (formal fitting errors only). These place LS IV-14°116 very near the region of maximum instability in the T_eff-log g plane for short-period p-mode pulsators of the hot subdwarf type. If the luminosity variations are indeed due to pulsations, then LS IV-14°116 poses a real challenge to current theory: how can such long observed periods (which would have to be associated with medium- to high-order g-modes) be excited at such a high effective temperature and surface gravity, while the short-period p-modes, more typically excited in this domain, are not observed in this particular star?