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تسجيل مستخدم جديدSub-Chandrasekhar progenitors favoured for type Ia supernovae: Evidence from late-time spectroscopy
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A non-local-thermodynamic-equilibrium (NLTE) level population model of the first and second ionisation stages of iron, nickel and cobalt is used to fit a sample of XShooter optical + near-infrared (NIR) spectra of Type Ia supernovae (SNe Ia). From the ratio of the NIR lines to the optical lines limits can be placed on the temperature and density of the emission region. We find a similar evolution of these parameters across our sample. Using the evolution of the Fe II 12$,$570$,mathring{A},$to 7$,$155$,mathring{A},$line as a prior in fits of spectra covering only the optical wavelengths we show that the 7200$,mathring{A},$feature is fully explained by [Fe II] and [Ni II] alone. This approach allows us to determine the abundance of Ni II$,$/$,$Fe II for a large sample of 130 optical spectra of 58 SNe Ia with uncertainties small enough to distinguish between Chandrasekhar mass (M$_{text{Ch}}$) and sub-Chandrasekhar mass (sub-M$_{text{Ch}}$) explosion models. We conclude that the majority (85$%$) of normal SNe Ia have a Ni/Fe abundance that is in agreement with predictions of sub-M$_{text{Ch}}$ explosion simulations of $sim Z_odot$ progenitors. Only a small fraction (11$%$) of objects in the sample have a Ni/Fe abundance in agreement with M$_{text{Ch}}$ explosion models.
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There is no consensus on the progenitors of Type Ia supernovae (SNe Ia) despite their importance for cosmology and chemical evolution. We address this question by using our previously published catalogs of Mg, Si, Ca, Cr, Fe, Co, and Ni abundances in
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There are two classes of viable progenitors for normal Type Ia supernovae (SNe Ia): systems in which a white dwarf explodes at the Chandrasekhar mass ($M_{ch}$), and systems in which a white dwarf explodes below the Chandrasekhar mass (sub-$M_{ch}$).
It is not clear which of these channels is dominant; observations and light curve modeling have provided evidence for both. Here we use an extensive grid of 4500 time-dependent, multiwavelength radiation transport simulations to show that the sub-$M_{ch}$ model can reproduce the entirety of the width-luminosity relation (WLR), while the $M_{ch}$ model can only produce the brighter events $(0.8 < Delta M_{15}(B) < 1.55)$, implying that fast-declining SNe Ia come from sub-$M_{ch}$ explosions. We do not assume a particular theoretical paradigm for the progenitor or explosion mechanism, but instead construct parameterized models that vary the mass, kinetic energy, and compositional structure of the ejecta, thereby realizing a broad range of possible outcomes of white dwarf explosions. We provide fitting functions based on our large grid of detailed simulations that map observable properties of SNe Ia such as peak brightness and light curve width to physical parameters such as $^{56}mathrm{Ni}$ and total ejected mass. These can be used to estimate the physical properties of observed SNe Ia.
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