Opacity modelling of heavy-metal hot subdwarfs. Photoionization of Sr${}^0$, Y${}^{+}$ and Zr${}^{2+}$

Abstract

Heavy-metal hot subdwarfs (sdB and sdO) represent a small group of stars with unusually high concentrations of trans-iron elements in their atmospheres, having abundances ~ 10000 times solar. One example is LS IV-14${}^{\circ }$ 116, where a number of heavy-metal absorption lines of Sr II, Y III and Zr IV have been observed in the optical band 4000 - 5000 A. We use a fully relativistic Dirac atomic R-Matrix (DARC) to calculate photoionization cross sections of Sr${}^0$, Y${}^{+}$ and Zr${}^{2+}$ from their ground state to the twentieth excited level. We use the cross sections and the oscillator strengths to simulate the spectrum of a hot subdwarf. We obtain complete sets of photoionization cross sections for the three ions under study. We use these data to calculate the opacity of the stellar atmospheres of hot subdwarf stars, and show that for overabundances observed in some heavy-metal subdwarves, photo-excitation from zirconium, in particular, does contribute some back warming in the model.

arXiv comment8 pages, 6 figures, 6 tables

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Cited by in corpus (4)

• Hot subdwarf Atmospheric parameters, Kinematics, and Origins -- Based on 1587 hot subdwarf stars observed in Gaia DR2 and LAMOST DR7
• Heavy-metal enrichment of intermediate He-sdOB stars: the pulsators Feige 46 and LS IV -14 116 revisited
• The first heavy-metal hot subdwarf composite binary SB 744
• New Level Resolved Ground and Excited State Pb III, IV, V & VI Photoionization Cross Sections for Heavy Metal Subdwarf Modeling