Production of Silicon on Mass Increasing White Dwarfs -- Possible Origin of High-Velocity-Features in Type Ia Supernovae

Abstract

Type Ia supernovae (SNe Ia) often show high-velocity absorption features (HVFs) in their early phase spectra; however the origin of the HVFs is unknown. We show that a near-Chandrasekhar-mass white dwarf (WD) develops a silicon-rich layer on a carbon-oxygen (CO) core before it explodes as an SN Ia. We calculated the nuclear yields in successive helium shell flashes for 1.0 $M_{\odot }$, 1.2 $M_{\odot }$, and 1.35 $M_{\odot }$ CO WDs accreting helium-rich matter with several mass-accretion rates ranging from $1\times 10^{-7}{M}_{\odot }$ yr${}^{-1}$ to $7.5\times 10^{-7}{M}_{\odot }$ yr${}^{-1}$. For the $1.35M_{\odot }$ WD with the accretion rate of $1.6\times 10^{-7}{M}_{\odot }$ yr${}^{-1}$, the surface layer developed as helium burning ash and consisted of 40% ${}^{24}$Mg, 33% ${}^{12}$C, 23% ${}^{28}$Si, and a few percent of ${}^{20}$Ne by weight. For a higher mass accretion rate of $7.5\times 10^{-7}{M}_{\odot }$ yr${}^{-1}$, the surface layer consisted of 58% ${}^{12}$C, 31% ${}^{24}$Mg, and 0.43% ${}^{28}$Si. For the $1.2M_{\odot }$ WDs, silicon is produced only for lower mass accretion rates (2% for $1.6\times 10^{-7}{M}_{\odot }$ yr${}^{-1}$). No substantial silicon ($<0.07$) is produced on the $1.0M_{\odot }$ WD independently of the mass-accretion rate. If the silicon-rich surface layer is the origin of Si II HVFs, its characteristics are consistent with that of mass increasing WDs. We also discuss possible Ca production on very massive WDs ($\gtrsim 1.38M_{\odot }$).

17 pages, 18 figures, to appear in ApJ

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Cited by in corpus (13)

• Physics of nova outbursts: A theoretical model of classical nova outbursts with self-consistent wind mass loss
• Near-Chandrasekhar-Mass Type Ia Supernovae from the Double-Degenerate Channel
• Population synthesis of accreting white dwarfs: Rates and evolutionary pathways of H and He novae
• The impact of metallicity on nova populations
• The formation of type Ia supernovae from carbon-oxygen-silicon white dwarfs
• R-mode oscillations in accreting white dwarfs in cataclysmic variables
• Off-centre carbon burning in He-accreting carbon-oxygen white dwarfs
• A study of Si II and S II features in spectra of Type Ia supernova
• High-velocity feature as the indicator of the stellar population of Type Ia supernovae
• Exploring the shell model of high-velocity features of Type Ia supernovae using TARDIS
• He-shell flashes on the surface of oxygen-neon white dwarfs
• A helium nova in the Large Magellanic Cloud -- the faint supersoft X-ray source [HP99]159
• Puzzling High-Velocity Calcium Absorption Features Of Type Ia Supernovae