Manganese spread in Ursa Minor as a proof of sub-classes of type Ia supernovae
1 INAF–Osservatorio Astronomico di Trieste, 34131 Trieste, Italy
2 Centre for Astrophysics Research, School of Physics, Astronomy and Mathematics, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
Received: 19 June 2017
Accepted: 24 August 2017
Context. Recently, new sub-classes of Type Ia supernovae (SNe Ia) were discovered, including SNe Iax. The suggested progenitors of SNe Iax are relatively massive, possibly hybrid C+O+Ne white dwarfs, which can cause white dwarf winds at low metallicities. There is another class that can potentially occur at low or zero metallicities; sub-Chandrasekhar mass explosions in single and/or double degenerate systems of standard C+O white dwarfs. These explosions have different nucleosynthesis yields compared to the normal, Chandrasekhar mass explosions.
Aims. We test these SN Ia channels using their characteristic chemical signatures.
Methods. The two sub-classes of SNe Ia are expected to be rarer than normal SNe Ia and do not affect the chemical evolution in the solar neighbourhood; however, because of the shorter delay time and/or weaker metallicity dependence, they could influence the evolution of metal-poor systems. Therefore, we have included both in our stochastic chemical evolution model for the dwarf spheroidal galaxy Ursa Minor.
Results. The model predicts a butterfly-shape spread in [Mn/Fe] in the interstellar medium at low metallicity and – at the same time – a decrease of [α/Fe] ratios at lower [Fe/H] than in the solar neighbourhood, both of which are consistent with the observed abundances in stars of Ursa Minor.
Conclusions. The surprising agreement between our models and available observations provides a strong indication of the origins of these new sub-classes of SNe Ia. This outcome requires confirmation by future abundance measurements of manganese in stars of other satellite galaxies of our Milky Way. It will be vital for this project to measure not the most extreme metal-poor tail, as more commonly happens, but the opposite; the metal-rich end of dwarf spheroidals.
Key words: galaxies: evolution / galaxies: dwarf / stars: abundances / nuclear reactions, nucleosynthesis, abundances / supernovae: general
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