Author ORCID Identifier
Monthly Notices of the Royal Astronomical Society
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 Teff=38 900±270 K, logg/cms−2=5.97±0.11, log nHe/nH = −0.57 ± 0.01, EB − V ≈ 0.03, and angular radius θ = 1.062 ± 0.006 × 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.
Jeffery, C. S.; Baran, A. S.; Behara, N. T.; Kvammen, A.; Martin, P.; N., Naslim; Østensen, R. H.; Preece, H. P.; Reed, M. D.; Telting, J. H.; and Woolf, V. M., "Discovery of a variable lead-rich hot subdwarf: UVO 0825+15" (2016). Physics Faculty Publications. 54.
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