Eta Carinae: A Tale of Two Periastron Passages
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Date
2021-12-14
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Citation of Original Publication
Theodore R. Gull et al. Eta Carinae: A Tale of Two Periastron Passages. The Astrophysical Journal 923 (Dec. 14, 2021) No. 1. https://iopscience.iop.org/article/10.3847/1538-4357/ac22a6/meta.
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This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
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Abstract
Since 2002, the far-ultraviolet (FUV) flux (1150–1680 Å) of Eta Carinae, monitored by the Hubble Space
Telescope/Space Telescope Imaging Spectrograph, has increased by an order of magnitude. This increase is
attributed to partial dissipation of a line-of-sight (LOS) occulter that blocks the central core of the system. Across
the 2020 February periastron passage, changes in the FUV emission show a stronger wavelength dependence than
occurred across the 2003 July periastron passage. Across both periastron passages, most of the FUV spectrum
dropped in flux then recovered a few months later. The 2020 periastron passage included enhancements of FUV
flux in narrow spectral intervals near periastron followed by a transient absorption and recovery to pre-periastron
flux levels. The drop in flux is due to increased absorption by singly ionized species as the secondary star plunges
deep into the wind of the primary star, which blocks the companion’s ionizing radiation. The enhanced FUV
emission is caused by the companion’s wind-blown cavity briefly opening a window to deeper layers of the
primary star. This is the first time transient brightening has been seen in the FUV comparable to transients
previously seen at longer wavelengths. Changes in resonance line-velocity profiles hint that the dissipating occulter
is associated with material in LOS moving at −100 to −300 km s−1
, similar in velocity of structures previously
associated with the 1890s lesser eruption.