Abstract

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 Teff38900±270 K, log g/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.

Department(s)

Physics, Astronomy, and Materials Science

Document Type

Article

DOI

https://doi.org/10.1093/mnras/stw2852

Rights Information

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2016 The authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

Keywords

chemically peculiar stars, early-type stars, UVO 0825+15, oscillations, subdwarfs, variables stars

Publication Date

2016

Recommended Citation

Jeffery, C. S., A. S. Baran, N. T. Behara, A. Kvammen, P. Martin, R. H. Østensen, H. P. Preece, M. D. Reed, J. H. Telting, and V. M. Woolf. "Discovery of a variable lead-rich hot subdwarf: UVO 0825+ 15." Monthly Notices of the Royal Astronomical Society (2016).

Journal Title

Monthly Notices of the Royal Astronomical Society

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