The chemical signature of SNIax in the stars of Ursa minor?

Abstract

Recently, a new class of supernovae Ia was discovered: the supernovae Iax; the increasing sample of these objects share common features as lower maximum-light velocities and typically lower peak magnitudes. In our scenario, the progenitors of the SNe Iax are very massive white dwarfs, possibly hybrid C+O+Ne white dwarfs; due to the accretion from a binary companion, they reach the Chandrasekhar mass and undergo a central carbon deflagration, but the deflagration is quenched when it reaches the outer O +Ne layer. This class of SNe Ia are expected to be rarer than standard SNe Ia and do not affect the chemical evolution in the solar neighbourhood; however, they have a short delay time and they could influence the evolution of metal-poor systems. Therefore, we have included in a stochastic chemical evolution model for the dwarf spheroidal galaxy Ursa minor the contribution of SNe Iax. The model predicts a spread in [Mn/Fe] in the ISM medium at low metallicity and - at the same time - a decrease of the [alpha/Fe] elements, as in the classical time delay model. This is in surprising agreement with the observed abundances in stars of Ursa minor and provide a strong indication to the origin of this new classes of SNIa.