2023/11/22 by K. Werner, Werner, Klaus, Nicole Reindl +7 · 1 citation
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #FOS: Physical sciences #Solar and Stellar Astrophysics (astro-ph.SR) #Stellar, planetary, and galactic studies
paper · pdf · doi:10.48550/arxiv.2311.13388
openalex publication_date 2023/11/22 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We perform nonlocal thermodynamic equilibrium (NLTE) model atmosphere analyses of the three hottest hypervelocity stars (space velocities between ≈ 1500-2800 km s-1) known to date, which were recently discovered spectroscopically and identified as runaways from Type Ia supernovae. The hottest of the three (J0546+0836, effective temperature Teff = 95,000 ± 15,000 K, surface gravity log g = 5.5 ± 0.5) has an oxygen-dominated atmosphere with a significant amount of carbon (C = 0.10 ± 0.05, O = 0.90 ± 0.05, mass fractions). Its mixed absorption+emission line spectrum exhibits photospheric absorption lines from O V and O VI as well as O III and O IV emission lines that are formed in a radiation-driven wind with a mass-loss rate of the order of 10-8 M_\odot yr-1. Spectroscopically, J0546+0836 is a [WC]-PG1159 transition-type pre-white dwarf. The second object (J0927-6335) is a PG1159-type white dwarf with a pure absorption-line spectrum dominated by C III/C IV and O III/O IV. We find Teff = 60,000 ± 5000 K, log g = 7.0 ± 0.5, and a carbon- and oxygen-dominated atmosphere with C = 0.47 ± 0.25, O = 0.48 ± 0.25, and possibly a minute amount of helium (He = 0.05 ± 0.05). Comparison with post-AGB evolutionary tracks suggests a mass of M≈0.5 M_\odot for both objects, if such tracks can safely be applied to these stars. We find the third object (J1332-3541) to be a relatively massive (M=0.89 M_\odot) hydrogen-rich (DAO) white dwarf with Teff = 65,657 ± 2390 K, log g = 8.38 ± 0.08, and abundances H = 0.65 ± 0.04 and He = 0.35 ± 0.04. We discuss our results in the context of the "dynamically driven double-degenerate double-detonation" (D6) scenario proposed for the origin of these stars.