Eta Carinae & the Homunculus: Far Infrared, Sub-millimeter Spectral Lines

Abstract

The evolved massive binary star Eta Carinae underwent eruptive mass loss events that formed the complex bi-polar Homunculus nebula harboring tens of solar masses of unusually nitrogen-rich gas and dust. Despite expectations for the presence of a significant molecular component to the gas, detections have been observationally challenged by limited access to the far-infrared and the intense thermal continuum. A spectral survey of the atomic and rotational molecular transitions was carried out with the Herschel Space Observatory, revealing a rich spectrum of broad emission lines originating in the ejecta. Velocity profiles of selected PACS lines correlate well with known substructures: H I in the central core; NH and weak [C II] within the Homunculus; and [N II] emissions in fast-moving structures external to the Homunculus. We have identified transitions from [O I], H I, and 18 separate light C- and O-bearing molecules including CO, CH, CH+, and OH, and a wide set of N-bearing molecules, NH, NH+, N2H+, NH2, NH3, HCN, HNC, CN, and N2H+. Half of these are new detections unprecedented for any early-type massive star environment. A very low ratio [12C/13C] LE 4 is estimated from five molecules and their isotopologues. We demonstrate that non-LTE effects due to the strong continuum are significant. Abundance patterns are consistent with line formation in regions of carbon and oxygen depletions with nitrogen enhancements, reflecting an evolved state of the erupting star with efficient transport of CNO-processed material to the outer layers. The results offer many opportunities for further observational and theoretical investigations of the molecular chemistry under extreme physical and chemical conditions around massive stars in their final stages of evolution.

arXiv comment37 pages, 16 figures, 5 tables, accepted MNRAS

References in corpus (53)

• Herschel Space Observatory - An ESA facility for far-infrared and submillimetre astronomy
• The Photodetector Array Camera and Spectrometer (PACS) on the Herschel Space Observatory
• The Herschel-SPIRE instrument and its in-flight performance
• Grids of stellar models with rotation - I. Models from 0.8 to 120 Msun at solar metallicity (Z = 0.014)
• A computer program for fast non-LTE analysis of interstellar line spectra
• The Wavelength Dependence of Interstellar Extinction from 1.25 to 8.0 microns Using GLIMPSE Data
• Diagnostics of irradiated dense gas in galaxy nuclei. II. A grid of XDR and PDR models
• The Unprecedented 2012 Outburst of SN 2009ip: A Luminous Blue Variable Becomes a True Supernova
• Molecular excitation in the Interstellar Medium: recent advances in collisional, radiative and chemical processes
• The Structure of the Homunculus: I. Shape and Latitude Dependence from H2 and [Fe II] Velocity Maps of Eta Carinae
• In-flight calibration of the Herschel-SPIRE instrument
• In Hot Pursuit of the Hidden Companion of Eta Carinae: An X-ray Determination of the Wind Parameters
• The evolution of massive stars and their spectra I. A non-rotating 60 Msun star from the zero-age main sequence to the pre-supernova stage
• Interstellar Hydrides
• The chemistry of vibrationally excited H2 in the interstellar medium
• The far-IR spectrum of Sagittarius B2 region: Extended molecular absorption, photodissociation and photoionization
• Dissecting the Homunculus nebula around Eta Carinae with spatially resolved near-infrared spectroscopy
• A Blast Wave from the 1843 Eruption of Eta Carinae
• High-excitation emission lines near eta Carinae, and its likely companion star
• The Binarity of Eta Carinae Revealed from Photoionization Modeling of the Spectral Variability of the Weigelt Blobs B and D
• Nitrogen hydrides in interstellar gas II. Analysis of Herschel/HIFI observations towards W49N and G10.6-0.4 (W31C)
• Constraints on decreases in Eta Carinae's mass loss from 3D hydrodynamic simulations of its binary colliding winds
• Nitrogen hydrides in the cold envelope of IRAS16293-2422
• Light-echoes from the plateau in Eta Carinae's Great Eruption reveal a two-stage shock-powered event
• Calibration of the Herschel SPIRE Fourier Transform Spectrometer
• On the influence of the companion star in Eta Carinae: 2D radiative transfer modeling of the ultraviolet and optical spectra
• Nitrogen and Oxygen Abundance Variations in the Outer Ejecta of Eta Carinae: Evidence for Recent Chemical Enrichment
• The sub-arcsecond dusty environment 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
• Identification of Emission Lines in the Low-Ionization Strontium Filament Near Eta Carinae
• Observing Extended Sources with the \Herschel SPIRE Fourier Transform Spectrometer
• $\eta$ Carinae's Dusty Homunculus Nebula from Near-Infrared to Submillimeter Wavelengths: Mass, Composition, and Evidence for Fading Opacity
• Ancient eruptions of Eta Carinae: A tale written in proper motions
• The three-dimensional structure of the Eta Carinae Homunculus
• The fossil wind structures of Eta Carinae: changes across on 5.54-year cycle
• $\eta$ Carinae Baby Homunculus Uncovered by ALMA
• Distinguishing Circumstellar from Stellar Photometric Variability in Eta Carinae
• A disrupted molecular torus around Eta Carinae as seen in 12CO with ALMA
• Systematic characterisation of the Herschel SPIRE Fourier Transform Spectrometer
• Cleaning up Eta Carinae: Detection of Ammonia in the Homunculus
• Penetrating the Homunculus -- Near-Infrared Adaptive Optics Images of Eta Carinae
• Opening the Treasure Chest in Carina
• Molecules in η 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
• Detection of the compressed primary stellar wind in eta Carinae
• Deep Herschel PACS point spread functions
• Discovery of CH and OH in the -513 km s-1 Ejecta of Eta Carinae
• CO, Water, and Possible Methanol in Eta Carinae Approaching Periastron
• Dissecting a SN impostor's circumstellar medium: MUSEing about the SHAPE of eta Car's outer ejecta
• Spatial distribution and kinematics of the molecular material associated with $\eta$ Carinae
• Correcting the extended-source calibration for the Herschel-SPIRE Fourier-Transform Spectrometer
• 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

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