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CO, Water, and Tentative Methanol in η Carinae Approaching Periastron

Morris, Patrick W. and Charnley, Steven B. and Corcoran, Michael and Cordiner, Martin and Damineli, Augusto and Groh, Jose H. and Gull, Theodore R. and Loinard, Laurent and Madura, Thomas and Mehner, Andrea and Moffat, Anthony and Palmer, Maureen Y. and Rau, Gioia and Richardson, Noel D. and Weigelt, Gerd (2020) CO, Water, and Tentative Methanol in η Carinae Approaching Periastron. Astrophysical Journal Letters, 892 (2). Art. No. L23. ISSN 2041-8213.

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The complex circumstellar environment around the massive binary and luminous blue variable η Carinae is known to harbor numerous light molecules, emitting most strongly in rotational states with upper level energies to ~300 K. In circumstellar gas, the complex organic molecule methanol (CH₃OH) has been found almost exclusively around young stellar objects, and thus regarded as a signpost of recent star formation. Here we report the first potential detection of methanol around a highly evolved high-mass star, while using the Atacama Large Millimeter Array to investigate molecular cloud conditions traced by CO (2–1) in an orbit phase preceding the 2020 periastron. The methanol emission originates from hot (T_(gas) ≃ 700 K) material, ~2'' (0.02 pc) across, centered on the dust-obscured binary, and is accompanied by prominent absorption of continuum radiation in a cooler (T_(gas) ≃ 110 K) layer of gas. We also report a first detection of water in Herschel observations at 557 and 988 GHz. The methanol abundance is several to 50 times higher than observed toward several lower-mass stars, while water abundances are similar to those observed in cool, dense molecular clouds. The very high methanol:water abundance ratio in the core of η Car may suggest methanol formation processes similar to Fischer–Tropsch-type catalytic reactions on dust grains. These observations prove that complex molecule formation can occur in a chemically evolved massive stellar environment, given sufficient gas densities and shielding conditions as may occur in material around massive interacting companions and merger remnants.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Morris, Patrick W.0000-0002-5186-4381
Corcoran, Michael0000-0002-7762-3172
Cordiner, Martin0000-0001-8233-2436
Damineli, Augusto0000-0002-7978-2994
Gull, Theodore R.0000-0002-6851-5380
Loinard, Laurent0000-0002-5635-3345
Mehner, Andrea0000-0002-9564-3302
Rau, Gioia0000-0002-3042-4539
Richardson, Noel D.0000-0002-2806-9339
Weigelt, Gerd0000-0001-9754-2233
Alternate Title:CO, Water, and Possible Methanol in Eta Carinae Approaching Periastron, CO, Water, and Possible Methanol in η Carinae Approaching Periastron
Additional Information:© 2020 The American Astronomical Society. Received 2019 November 20; revised 2020 February 19; accepted 2020 February 20; published 2020 March 31. The authors express their appreciation to Pierre Cox, Zulema Abraham, and Pedro Paulo Bonetti Beaklini for productive discussions on the ALMA observations, and Darius Liz for cautionary words on the water OPR. We also thank our anonymous referee for comments leading to important improvements in the manuscript. This paper makes use of the following ALMA data: ADS/JAO.ALMA #2018.A.00026.S and ADS/JAO.ALMA #2013.1.00661.S. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. We have also made use of observations obtained from the Herschel Space Observatory. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. A.D. thanks to the National Concil for Scientific and Technological Development (CNPq) and to Fundação de Amparoá Pesquisa do Estado de São Paulo (FAPESP) for continuing support.
Funding AgencyGrant Number
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)UNSPECIFIED
Fundação de Amparo à Pesquisa do Estado de Sao Paulo (FAPESP)UNSPECIFIED
Subject Keywords:Circumstellar matter ; Molecule formation ; Astrochemistry ; Reaction catalysts ; Massive stars ; Luminous blue variable stars
Issue or Number:2
Classification Code:Unified Astronomy Thesaurus concepts: Circumstellar matter (241); Molecule formation (2076); Astrochemistry (75); Reaction catalysts (2080); Massive stars (732); Luminous blue variable stars (944)
Record Number:CaltechAUTHORS:20200401-070803450
Persistent URL:
Official Citation:Patrick W. Morris et al 2020 ApJL 892 L23
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:102212
Deposited By: Tony Diaz
Deposited On:01 Apr 2020 15:27
Last Modified:24 Jun 2020 17:33

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