Discovery of a variable lead-rich hot subdwarf: UVO 0825+15

C. S. Jeffery, A. S. Baran, N. T. Behara, A. Kvammen, P. Martin, N. Naslim, R. H. Østensen, H. P. Preece, M. D. Reed, J. H. Telting, V. M. Woolf

Research output: Contribution to journalArticlepeer-review

44 Citations (Scopus)

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 Teff = 38 900 ± 270 K, log g/cm s-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 blueoptical 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 ismultiperiodic non-radial oscillation due to gmodes 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.

Original languageEnglish
Pages (from-to)3101-3124
Number of pages24
JournalMonthly Notices of the Royal Astronomical Society
Volume465
Issue number3
DOIs
Publication statusPublished - Mar 1 2017
Externally publishedYes

Keywords

  • Stars: chemically peculiar
  • Stars: early-type
  • Stars: individual: UVO 0825+15
  • Stars: oscillations
  • Stars: variables: general
  • Subdwarfs

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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