ALMA spectral survey of Supernova 1987A – molecular inventory, chemistry, dynamics and explosive nucleosynthesis

Journal article

We report the first molecular line survey of Supernova 1987A in the millimetre wavelength range. In the Atacama Large Millimeter/submillimeter Array (ALMA) 210–300 and 340–360 GHz spectra, we detected cold (20–170 K) CO, ²⁸SiO, HCO⁺ and SO, with weaker lines of ²⁹SiO from ejecta. This is the first identification of HCO⁺ and SO in a young supernova remnant. We find a dip in the J = 6–5 and 5–4 SiO line profiles, suggesting that the ejecta morphology is likely elongated. The difference of the CO and SiO line profiles is consistent with hydrodynamic simulations, which show that Rayleigh–Taylor instabilities cause mixing of gas, with heavier elements much more disturbed, making more elongated structure. We obtained isotopologue ratios of ²⁸SiO/²⁹SiO > 13, ²⁸SiO/³⁰SiO > 14 and ¹²CO/¹³CO > 21, with the most likely limits of ²⁸SiO/²⁹SiO >128, ²⁸SiO/³⁰SiO >189. Low ²⁹Si and ³⁰Si abundances in SN 1987A are consistent with nucleosynthesis models that show inefficient formation of neutron-rich isotopes in a low-metallicity environment, such as the Large Magellanic Cloud. The deduced large mass of HCO⁺ (∼5 × 10⁻⁶ M_⊙) and small SiS mass (<6 × 10⁻⁵ M_⊙) might be explained by some mixing of elements immediately after the explosion. The mixing might have caused some hydrogen from the envelope to sink into carbon- and oxygen-rich zones after the explosion, enabling the formation of a substantial mass of HCO⁺. Oxygen atoms may have penetrated into silicon and sulphur zones, suppressing formation of SiS. Our ALMA observations open up a new window to investigate chemistry, dynamics and explosive nucleosynthesis in supernovae.

Authors: Matsuura, M; Indebetouw, R; Woosley, S; Bujarrabal, V; Abellán, F

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Oxford University Press
• Journal: Monthly Notices of the Royal Astronomical Society
• Volume: 469
• Issue: 3
• Pages: 3347-3362
• Publication date: 2017-04-05
• Acceptance date: 2017-03-31
• DOI: 10.1093/mnras/stx830
• EISSN: 1365-2966
• ISSN: 0035-8711
• Language: English
• Keywords: individual supernovae; abundances; Supernova 1987A; ISM; supernovae; stars; supernova remnants; radio lines; molecules