Spectroscopic Signatures of the Vanishing Natural Coronagraph of eta Carinae. (arXiv:2105.00590v3 [astro-ph.SR] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Damineli_A/0/1/0/all/0/1">A. Damineli</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Navarete_F/0/1/0/all/0/1">F. Navarete</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hillier_D/0/1/0/all/0/1">D. J. Hillier</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Moffat_A/0/1/0/all/0/1">A. F. J. Moffat</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Corcoran_M/0/1/0/all/0/1">M. F. Corcoran</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gull_T/0/1/0/all/0/1">T. R. Gull</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Richardson_N/0/1/0/all/0/1">N. D. Richardson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Weigelt_G/0/1/0/all/0/1">G. Weigelt</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Morris_P/0/1/0/all/0/1">P. W. Morris</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Stevens_I/0/1/0/all/0/1">I. Stevens</a>
Eta Carinae is a massive interacting binary system shrouded in a complex
circumstellar environment whose evolution is the source of the long-term
brightening observed during the last 80 years. An occulter, acting as a natural
coronagraph, impacts observations from our perspective, but not from most other
directions. Other sight-lines are visible to us through studies of the
Homunculus reflection nebula. The coronagraph appears to be vanishing,
decreasing the extinction towards the central star, and causing the star’s
secular brightening. In contrast, the Homunculus remains at an almost constant
brightness. The coronagraph primarily suppresses the stellar continuum, to a
lesser extent the wind lines, and not the circumstellar emission lines. This
explains why the absolute values of equivalent widths (EWs) of the emission
lines in our direct view are larger than those seen in reflected by the
Homunculus, why the direct view absolute EWs are decreasing with time, and why
lower-excitation spectral wind lines formed at larger radii (e.g. FeII 4585A)
decrease in intensity at a faster pace than higher excitation lines that form
closer to the star (e.g. Hdelta). Our main result is that the star, despite
its 10-fold brightening over two decades, is relatively stable. A vanishing
coronagraph that can explain both the large flux evolution and the much weaker
spectral evolution. This is contrary to suggestions that the long-term
variability is intrinsic to the primary star that is still recovering from the
Great Eruption with a decreasing mass-loss rate and a polar wind that is
evolving at a slower pace than at the equator.
Eta Carinae is a massive interacting binary system shrouded in a complex
circumstellar environment whose evolution is the source of the long-term
brightening observed during the last 80 years. An occulter, acting as a natural
coronagraph, impacts observations from our perspective, but not from most other
directions. Other sight-lines are visible to us through studies of the
Homunculus reflection nebula. The coronagraph appears to be vanishing,
decreasing the extinction towards the central star, and causing the star’s
secular brightening. In contrast, the Homunculus remains at an almost constant
brightness. The coronagraph primarily suppresses the stellar continuum, to a
lesser extent the wind lines, and not the circumstellar emission lines. This
explains why the absolute values of equivalent widths (EWs) of the emission
lines in our direct view are larger than those seen in reflected by the
Homunculus, why the direct view absolute EWs are decreasing with time, and why
lower-excitation spectral wind lines formed at larger radii (e.g. FeII 4585A)
decrease in intensity at a faster pace than higher excitation lines that form
closer to the star (e.g. Hdelta). Our main result is that the star, despite
its 10-fold brightening over two decades, is relatively stable. A vanishing
coronagraph that can explain both the large flux evolution and the much weaker
spectral evolution. This is contrary to suggestions that the long-term
variability is intrinsic to the primary star that is still recovering from the
Great Eruption with a decreasing mass-loss rate and a polar wind that is
evolving at a slower pace than at the equator.
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