SUBCLASSES OF TYPE IA SUPERNOVAE AS THE ORIGIN OF [alpha/FE] RATIOS IN DWARF SPHEROIDAL GALAXIES

Abstract

Recent extensive observations of Type Ia Supernovae (SNe Ia) have revealed the existence of a diversity of SNe Ia, including SNe Iax. We introduce two possible channels in the single degenerate scenario: (1) double detonations in sub-Chandrasekhar (Ch) mass CO white dwarfs (WDs), where a thin He envelope is developed with relatively low accretion rates after He novae even at low metallicities, and (2) carbon deflagrations in Ch-mass, possibly hybrid C+O+Ne WDs, where WD winds occur at [Fe/H] at high accretion rates. These subclasses of SNe Ia are rarer than "normal" SNe Ia and do not affect the chemical evolution in the solar neighborhood, but can be very important in metal-poor systems with stochastic star formation. In dwarf spheroidal galaxies in the Local Group, the decrease of [α/Fe] ratios at [Fe/H] to -1.5 can be produced depending on the star formation history. SNe Iax give high [Mn/Fe], while sub-Ch-mass SNe Ia give low [Mn/Fe], and thus a model including a mix of the two is favored by the available observations.