Neon and CNO Abundances for Extreme Helium Stars -- A Non-LTE Analysis

Abstract

A non-LTE (NLTE) abundance analysis was carried out for three extreme helium stars (EHes): BD+10 2179, BD-9 4395, and LS IV+6 002, from their optical spectra with NLTE model atmospheres. NLTE TLUSTY model atmospheres were computed with H, He, C, N, O, and Ne treated in NLTE. Model atmosphere parameters were chosen from consideration of fits to observed He I line profiles and ionization equilibria of C and N ions. The program SYNSPEC was then used to determine the NLTE abundances for Ne as well as H, He, C, N, and O. LTE neon abundances from Ne I lines in the EHes: LSE 78, V1920 Cyg, HD 124448, and PV Tel, are derived from published models and an estimate of the NLTE correction applied to obtain the NLTE Ne abundance. We show that the derived abundances of these key elements, including Ne, are well matched with semi-quantitative predictions for the EHe resulting from a cold merger (i.e., no nucleosynthesis during the merger) of a He white dwarf with a C-O white dwarf.

Astrophysical Journal, accepted

References in corpus (6)

• A Grid of NLTE Line-Blanketed Model Atmospheres of Early B-type Stars
• Neon Abundances in B-Stars of the Orion Association: Solving the Solar Model Problem?
• Carbon abundances of early B-type stars in the solar vicinity. Non-LTE line-formation for C II/III/IV and self-consistent atmospheric parameters
• Fluorine in R Coronae Borealis Stars
• The neon content of nearby B-type stars and its implications for the solar model problem
• Abundance analysis of cool extreme helium star: LSS 3378

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