2017MNRAS.465.3101J

UVO 0825+15 is a hot bright helium-rich subdwarf which lies in K2 Field 5 and in a sample of intermediate helium-rich subdwarfs observed the Subaru High Dispersion Spectrograph. The K2 light curve shows low-amplitude variations, whilst the Subaru spectrum shows Pb IV absorption lines, indicative of a very high lead overabundance. UVO 0825+15 also has a high proper motion with kinematics typical for a thick disc star. Analyses of ultraviolet and intermediate dispersion optical spectra rule out a short-period binary companion and provide fundamental atmospheric parameters of { T_eff}=38 900± 270 K, { log g/cm/s2=5.97± 0.11, log n_He/n_H = -0.57 ± 0.01, E_B - V_ ≃ 0.03, and angular radius θ = 1.062 ± 0.006 x 10^–11 radians (formal errors). The high-resolution spectrum shows that carbon is > 2 dex subsolar, iron is approximately solar, and all other elements heavier than argon are at least 2-4 dex overabundant, including germanium, yttrium and lead. Approximately 150 lines in the blue-optical spectrum remain unidentified. The chemical structure of the photosphere is presumed to be determined by radiatively dominated diffusion. The K2 light curve shows a dominant period around 10.8 h, with a variable amplitude, its first harmonic, and another period at 13.3 h. The preferred explanation is multiperiodic non-radial oscillation due to g modes with very high radial order, although this presents difficulties for pulsation theory. Alternative explanations fail for lack of radial-velocity evidence. UVO 0825+15 represents the fourth member of a group of hot subdwarfs having helium-enriched photospheres and 3-4 dex overabundances of trans-iron elements and is the first lead-rich subdwarf to show evidence of pulsations.