New Level Resolved Ground and Excited State Pb III, IV, V & VI Photoionization Cross Sections for Heavy Metal Subdwarf Modeling

Abstract

High abundances of various lead (Pb) species have been identified in the spectra of many Asymptotic Giant Branch (AGB) stars and O- and B-type subdwarfs (sdO/B). Additional atomic data relating to Pb, and in particular photoionization cross sections, are needed to allow a greater understanding of the origin of these observed Pb abundances, and hence discern the evolutionary pathway of these stars. We have calculated level-resolved photoionization cross sections for Pb III, IV, V and VI. Four new target structures have been developed with the General Relativistic Atomic Structure Package (GRASP0), whose corresponding energy levels, Einstein A-coefficients and oscillator strengths have been found to be in good agreement with previous experimental and theoretical sources. The photoionization cross sections calculated using the Dirac Atomic R-matrix Codes (DARC) are available in TOPBASE format, and follow the trends expected for an isonuclear series. These new Pb data sets will now allow for the modelling of Pb abundances and line opacities under Non-Local Thermodynamic Equilibrium (non-LTE) conditions. Using the helium-rich hot subdwarf EC 22536-5304 as a test case, we show that there are noticeable differences in the Pb line profiles across the ultraviolet and optical wavelength regions under LTE and non-LTE conditions. There is both depletion and enrichment of individual Pb species. This highlights the importance of applying non-LTE conditions when modelling EC 22536-5304, as well as other O/B-type stars.

15 Pages, 13 Figures, 13 Tables

References in corpus (18)

• Spectroscopic identification of r-process nucleosynthesis in a double neutron star merger
• Abundance studies of sdB stars using UV echelle HST/STIS spectroscopy
• Discovery of extremely lead-rich subdwarfs: does heavy metal signal the formation of subdwarf B stars?
• Discovery of a variable lead-rich hot subdwarf: UVO 0825+15
• Hydrogen in hot subdwarfs formed by double helium white dwarf mergers
• Model Photospheres with Accelerated Lambda Iteration
• An evolutionary channel for CO-rich and pulsating He-rich subdwarfs
• Heavy-metal enrichment of intermediate He-sdOB stars: the pulsators Feige 46 and LS IV -14 116 revisited
• A search for heavy-metal stars: abundance analyses of hot subdwarfs with Subaru
• PHL 417: a zirconium-rich pulsating hot subdwarf (V366 Aquarid) discovered in K2 data
• Stellar laboratories. X. New Cu IV - VII oscillator strengths and the first detection of copper and indium in hot white dwarfs
• The origin of the lead-rich stars in Galactic halo: investigation of the model parameters for the s-process
• The first heavy-metal hot subdwarf composite binary SB 744
• Opacity modelling of heavy-metal hot subdwarfs. Photoionization of Sr${}^0$, Y${}^{+}$ and Zr${}^{2+}$
• Surface abundance and the hunt for stratification in chemically peculiar hot subdwarfs: PG 0909+276 and UVO 0512-08
• The Abundance of Lead in Four Metal-Poor Stars
• Detection of cesium in the atmosphere of the hot He-rich white dwarf HD 149499B
• Hot Subdwarf Stars