Evidence for a Sub-Chandrasekhar-mass Type Ia Supernova in the Ursa Minor Dwarf Galaxy

Evidence for a Sub-Chandrasekhar-mass Type Ia Supernova in the Ursa Minor Dwarf Galaxy

A long-standing problem is identifying the elusive progenitors of Type Ia supernovae (SNe Ia), which can roughly be split into Chandraksekhar and sub-Chandrasekhar-mass events. An important difference between these two cases is the nucleosynthetic yield, which is altered by the increased neutron exc...

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Bibliographic Details
Published in:The Astrophysical journal 2018-04, Vol.857 (2), p.97
Main Authors: McWilliam, Andrew, Piro, Anthony L., Badenes, Carles, Bravo, Eduardo
Format: Article
Language:eng
Subjects:
Astrophysics
Chemical composition
Copper
Detonation
Diagnostic systems
Dilution
Dwarf galaxies
Ejecta
Galaxies
galaxies: dwarf
Interstellar matter
Interstellar medium
Iron
Manganese
Metallicity
Nickel
Nuclear fusion
nuclear reactions, nucleosynthesis, abundances
Organic chemistry
Progenitors (astrophysics)
Stars & galaxies
stars: abundances
Supernova
Supernovae
supernovae: general
White dwarf stars
Zinc
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Summary:A long-standing problem is identifying the elusive progenitors of Type Ia supernovae (SNe Ia), which can roughly be split into Chandraksekhar and sub-Chandrasekhar-mass events. An important difference between these two cases is the nucleosynthetic yield, which is altered by the increased neutron excess in Chandrasekhar progenitors due to their pre-explosion simmering and high central density. Based on these arguments, we show that the chemical composition of the most metal-rich star in the Ursa Minor dwarf galaxy, COS 171, is dominated by nucleosynthesis from a low-metallicity, low-mass, sub-Chandrasekhar-mass SN Ia. Key diagnostic abundance ratios include Mn/Fe and Ni/Fe, which could not have been produced by a Chandrasekhar-mass SN Ia. Large deficiencies of Ni/Fe, Cu/Fe and Zn/Fe also suggest the absence of alpha-rich freeze-out nucleosynthesis, favoring low-mass white dwarf progenitors of SNe Ia, near 0.95 M , from comparisons to numerical detonation models. We also compare Mn/Fe and Ni/Fe ratios to the recent yields predicted by Shen et al., finding consistent results. To explain the [Fe/H] at −1.35 dex for COS 171 would require dilution of the SN Ia ejecta with ∼104 M of material, which is expected for an SN remnant expanding into a warm interstellar medium with n ∼ 1 cm−3. In the future, finding more stars with the unique chemical signatures we highlight here will be important for constraining the rate and environments of sub-Chandrasekhar SNe Ia.
ISSN:0004-637X
1538-4357