The fraction of type Ia supernovae exploding inside planetary nebulae   (SNIPs)
  Using three independent directions we estimate that the fraction of type Ia supernovae (SNe Ia) exploding inside planetary nebulae (PNe), termed SNIPs,is at least ~20%. Our three directions are as follows. (i) Taking the variable sodium absorption lines in some SN Ia to originate in a massive circumstellar matter (CSM), as has been claimed recently, we use the results of Sternberg et al. (2014) to imply that > ~20% of SN Ia occur inside a PN (or a PN descendant), hence classify them as SNIPs. (ii) We next use results that show that whenever there are hydrogen lines in SN Ia the hydrogen mass in the CSM is large (> 1 M_Sun), hence the explosion is a SNIP. We make the simplest assumption that the probability for explosion is constant in time for up to about 10^5 yrs after the merger of the core with the white dwarf (WD) in the frame of the core-degenerate scenario. This results with at least few x10 of SNe Ia that may have a SNIP origin. (iii) We examine the X-ray morphologies of 13 well-resolved close-by SN remnants (SNRs) Ia and derive a crude upper limit, according to which 10-30% of all SNRs Ia possess opposite ear-like features, which we take as evidence of SNIP origin. Our results, together with several other recent results, lead us to conclude that the two scenarios most contributing to SNe Ia are the core degenerate and the double degenerate scenarios. Together these two account for >95% of all SNe Ia. 
Danny Tsebrenko and Noam Soker (Technion, Israel)
astro-ph.SR astro-ph.HE