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Eta carinae and the homunculus: far infrared/submillimetre spectral lines detected with the Herschel Space Observatory

Gull, T. R. and Morris, P. W. and Black, J. H. and Nielsen, K. E. and Barlow, M. J. and Royer, P. and Swinyard, B. M. (2020) Eta carinae and the homunculus: far infrared/submillimetre spectral lines detected with the Herschel Space Observatory. Monthly Notices of the Royal Astronomical Society, 499 (4). pp. 5269-5301. ISSN 0035-8711. doi:10.1093/mnras/staa3113.

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The evolved massive binary star η Carinae underwent eruptive mass-loss events that formed the complex bi-polar ‘Homunculus’ nebula harbouring 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] ≤ 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.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper ItemHerschel data archives ItemISO data archives
Gull, T. R.0000-0002-6851-5380
Morris, P. W.0000-0002-5186-4381
Black, J. H.0000-0001-7221-7207
Barlow, M. J.0000-0002-3875-1171
Alternate Title:Eta Carinae & the Homunculus: Far Infrared, Sub-millimeter Spectral Lines
Additional Information:Published by Oxford University Press on behalf of The Royal Astronomical Society 2020. This work is written by (a) US Government employee(s) and is in the public domain in the US. Accepted 2020 October 2. Received 2020 September 30; in original form 2020 March 19. The content of this paper is based on observations with the Herschel Space Observatory, which is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. We have made use software in the Herschel Interactive Processing Environment (HIPE), which was a joint development by the Herschel Science Ground Segment Consortium, consisting of ESA, the NASA Herschel Science Center, and the HIFI, PACS and SPIRE consortia. TRG, KEN, and PM acknowledge partial financial support from NASA grant SCEX22012D for the Herschel programme OT1_tgull3. MJB acknowledges support from European Research Council Grant SNDUST ERC-2015-AdG-694520. TRG acknowledges the support of Onsala Observatory and Max Planck Institute for RadioAstronomy during visits at those institutions. We thank the referee for many useful comments leading to significant improvement of this paper. DATA AVAILABILITY. The observations presented in this paper are based on observations which are available in the public Herschel and ISO data archives Reasonable requests for advanced data products may be addressed to P.W.M.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
European Research Council (ERC)694520
Onsala ObservatoryUNSPECIFIED
Max Planck Institute for RadioAstronomyUNSPECIFIED
Subject Keywords:Stars: individual: Eta Carinae, stars: winds, outflows, ISM: individual objects: Homunculus, infrared: ISM, infrared: stars
Issue or Number:4
Record Number:CaltechAUTHORS:20210114-143038521
Persistent URL:
Official Citation:T R Gull, P W Morris, J H Black, K E Nielsen, M J Barlow, P Royer, B M Swinyard, Eta carinae and the homunculus: far infrared/submillimetre spectral lines detected with the Herschel Space Observatory, Monthly Notices of the Royal Astronomical Society, Volume 499, Issue 4, December 2020, Pages 5269–5301,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:107493
Deposited By: George Porter
Deposited On:15 Jan 2021 15:09
Last Modified:16 Nov 2021 19:03

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