FUV spectra of Δ Car, recorded across two decades with HST/STIS, document multiple changes in resonant lines caused by dissipating extinction in our line of sight. The FUV flux has increased nearly tenfold, which has led to increased ionization of the multiple shells within the Homunculus and photodestruction of H2. Comparison of observed resonant line profiles with CMFGEN model profiles allows separation of wind-wind collision and shell absorptions from the primary wind P Cygni profiles. The dissipating occulter preferentially obscured the central binary and interacting winds relative to the very extended primary wind. We are now able to monitor changes in the colliding winds with orbital phase. High-velocity transient absorptions occurred across the most recent periastron passage, indicating acceleration of the primary wind by the secondary wind, which leads to a downstream, high-velocity bow shock that is newly generated every orbital period. There is no evidence of changes in the properties of the binary winds.
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Physics and Astronomy
Theodore R. Gull, D. John Hillier, Henrik Hartman, Michael F. Corcoran, Augusto Damineli, David Espinoza-Galeas, Kenji Hamaguchi, Felipe Navarete, Krister Nielsen, Thomas Madura, Anthony F.J. Moffat, Patrick Morris, Noel D. Richardson, Christopher M.P. Russell, Ian R. Stevens, and Gerd Weigelt. "Eta Carinae: An Evolving View of the Central Binary, Its Interacting Winds and Its Foreground Ejecta" Astrophysical Journal (2022). https://doi.org/10.3847/1538-4357/ac74c2