Long-term evolution in ionization of ejecta illuminated by Eta Carinae

Abstract

Changes in the flux and spectrum of Eta Carinae since 1900 have been attributed to the evolution of the central binary by some. Others suggest evolution in the occulting ejecta. The brightness jump in the 1940s, which coincided with the appearance of narrow forbidden emission lines, may have been caused by the clearing and ionization of intervening circumstellar ejecta. The brightening changed at a slower pace up through forty years later. Here we continue earlier studies focused on the long-term showing that the forbidden line emission increased in the early 1990s with no noticeable increase in the brightness of the Homunculus. We interpret that the increase in narrow line emission is due to decreased extinction in the LOS from the central binary to the Weigelt clumps. In 2000, the central stellar core increased in brightness at a faster rate without associated changes in the Homunculus. By 2018, hundreds of narrow-line absorptions from singly-ionized metals in our LOS from Eta Carinae disappeared, thought to be caused by increased ionization of metals. These three events (1990, 2000, and 2018) are explained by the dissipation of circumstellar material within the Homunculus close to the binary. Combining these changes with the steadiness of the Homunculus and the primary winds over the past four decades indicates that circumstellar ejecta in our direction have been cleared.

26 pages, 8 figures, to appear in ApJ

References in corpus (10)

• Simulating the formation of $\eta$ Carinae's surrounding nebula through unstable triple evolution and stellar merger-induced eruption
• The Early Spectra of Eta Carinae 1892 to 1941 and the Onset of Its High Excitation Emission Spectrum
• The Chrysalis Opens? Photometry from the Eta Carinae HST Treasury Project, 2002-2006
• The fossil wind structures of Eta Carinae: changes across on 5.54-year cycle
• Long-Term Optical Monitoring of Eta Carinae. Multiband light curves for a complete orbital period
• Distinguishing Circumstellar from Stellar Photometric Variability in Eta Carinae
• A moderately precise dynamical age for the Homunculus of Eta Carinae based on 13 years of HST imaging
• Spectroscopic Signatures of the Vanishing Natural Coronagraph of eta Carinae
• On the changes in the physical properties of the ionized region around the Weigelt structures in Eta Carinae over the 5.54-yr spectroscopic cycle
• Changes in the Na D${}_1$ Absorption Components of $\eta$ Carinae Provide Clues on the Location of the Dissipating Central Occulter