Changes in the Na D${}_1$ Absorption Components of $\eta$ Carinae Provide Clues on the Location of the Dissipating Central Occulter

Abstract

The Na D absorption doublet in the spectrum of $\eta$ Carinae is complex, with multiple absorption features associated with the Great Eruption (1840s), the Lesser Eruption (1890s), and interstellar clouds. The velocity profile is further complicated by the P Cygni profile originating in the system's stellar winds and blending with the He I $\lambda$5876 profile. The Na D profile contains a multitude of absorption components, including those at velocities of $-$145 km s${}^{-1}$, $-$168 km s${}^{-1}$, and $+$87 km s${}^{-1}$ that we concentrate on in this analysis. Ground-based spectra recorded from 2008 to 2021 show significant variability of the $-$145 km s${}^{-1}$ absorption throughout long-term observations. In the high ionization phases of $\eta$ Carinae prior to the 2020 periastron passage, this feature disappeared completely but briefly reappeared across the 2020 periastron, along with a second absorption at $-$168 km s${}^{-1}$. Over the past few decades, $\eta$ Car has been gradually brightening demonstrated to be caused by a dissipating occulter. The decreasing absorption of the $-$145 km s${}^{-1}$ component, coupled with similar trends seen in absorptions of ultraviolet resonant lines, indicate that this central occulter was possibly a large clump associated with the Little Homunculus or another clump between the Little Homunculus and the star. We also report on a foreground absorption component at $+$87 km s${}^{-1}$. Comparison of Na D absorption in the spectra of nearby systems demonstrates that this red-shifted component likely originates in an extended foreground structure consistent with a previous ultraviolet spectral survey in the Carina Nebula.

arXiv comment8 figures, 13 pages plus online data, accepted to ApJ

References in corpus (28)

• CHIRON - A Fiber Fed Spectrometer for Precise Radial Velocities
• The Structure of the Homunculus: I. Shape and Latitude Dependence from H2 and [Fe II] Velocity Maps of Eta Carinae
• Eta Carinae: Binarity Confirmed
• On the nature of the prototype LBV AG Carinae I. Fundamental parameters during visual minimum phases and changes in the bolometric luminosity during the S-Dor cycle
• Remarks on statistical errors in equivalent widths
• The UV Scattering Halo of the Central Source Associated with Eta Carinae
• The Solar Neighborhood XLIX: Nine Giant Planets Orbiting Nearby K Dwarfs, and the CHIRON Spectrograph's Radial Velocity Performance
• On the influence of the companion star in Eta Carinae: 2D radiative transfer modeling of the ultraviolet and optical spectra
• A Change in the Physical State of $\eta$ Carinae?
• He II $\lambda$4686 emission from the massive binary system in $\eta$ Car: constraints to the orbital elements and the nature of the periodic minima
• Ancient eruptions of Eta Carinae: A tale written in proper motions
• A Sea Change in Eta Carinae
• On the nature of the prototype LBV AG Carinae II. Witnessing a massive star evolving close to the Eddington and bistability limits
• Eta Carinae's 2014.6 Spectroscopic Event: Clues to the Long-term Recovery from its Great Eruption
• Critical Differences and Clues in Eta Car's 2009 Event
• The fossil wind structures of Eta Carinae: changes across on 5.54-year cycle
• The 2018 Census of Luminous Blue Variables
• The H-alpha Variations of eta Carinae During the 2009.0 Spectroscopic Event
• Distinguishing Circumstellar from Stellar Photometric Variability in Eta Carinae
• To $v_{\infty }$ and beyond! The He I absorption variability across the 2014.6 periastron passage of $\eta$ Carinae
• Uncovering the orbital dynamics of stars hidden inside their powerful winds: application to $\eta$ Carinae and RMC 140
• Mid-infrared evolution of eta Car from 1968 to 2018
• BRITE-Constellation reveals evidence for pulsations in the enigmatic binary $\eta$ Carinae
• The Optical Wind Line Variability of $\eta$ Carinae During the 2009.0 Event
• Eta Carinae's Declining Outflow Seen in the UV, 2002-2015
• Spectroscopic Signatures of the Vanishing Natural Coronagraph of eta Carinae
• Probabilistic orbits and dynamical masses of emission-line binaries
• The Altered State of $\eta$Carinae: HST's Photometric Record 1998--2021

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