Manganese spread in Ursa Minor as a proof of sub-classes of type Ia
  supernovae
  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 metalpoor
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 [alpha/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 ourMilkyWay. 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.
