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 with Subaru/HDS .
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 disk star .
Analyses of ultraviolet and intermediate dispersion optical spectra rule out a short-period binary companion , and provide fundamental atmospheric parameters of \mbox { $T _ { eff } $ } = 38 900 \pm 270 K , \mbox { $ \log g / { cm s ^ { -2 } } $ } = 5.97 \pm 0.11 , \log n _ { He } / n _ { H } = -0.57 \pm 0.01 , E _ { B - V } \approx 0.03 , and angular radius \theta = 1.062 \pm 0.006 \times 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 multi-periodic 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 .