Institution: Astronomical Institute, University of Bonn (Germany)

Title: Formation of Neutron Stars: Ultra-stripped SNe and other Hot Scenarios.

Abstract:
Mass transfer from a helium star to a compact companion in a close binary can produce an ultra-stripped core (in some cases an almost naked metal core, barely above the Chandrasekhar-mass limit) which undergoes an iron-core collapse supernova (Fe CCSN). The resulting explosion leads to ejection of only 0.05-0.20 Msun of material and produces a low-mass neutron star, as well as an extremely fast and faint Type Ic SN light curve. We computed synthetic light curves and demonstrate that SN 2005ek could be explained by our model. We argue that the second explosion in some double neutron star systems (for example, the double pulsar PSR J0737- 3039B) was likely associated with an ultra-stripped SN Ic. New results of an ongoing systematic investigation of the progenitors of electron capture SNe versus Fe CCSNe in close binaries are discussed. The second topic of this talk is focused on the possibility of forming neutron stars via the accretion-induced collapse (AIC) of a massive ONeMg white dwarf. Both observational evidence and theoretical computations are discussed.