December 2, 2010
The Initial And Final State Of SNe La From The Single Degenerate Model
Type Ia supernovae (SNe Ia) play an important role as cosmological distance indicators and have been used successfully to determine cosmological parameters, which resulted in the discovery of the accelerating expansion of the Universe. However, the exact nature of SN Ia progenitors is still not well understood. There is a popular theory that SNe Ia originate from runaway thermonuclear events in carbon"“oxygen white dwarves (CO WD) in binary systems. The CO WD accretes material from its companion. When the CO WD increases its mass above the maximum stable mass, it will explode.
Based on the nature of the companions of the mass accreting WDs, two competing scenarios have been proposed, namely, the double-degenerate (DD) channel and the single degenerate (SD) channel. Using the SD framework, Meng & Yang (2010) developed a comprehensive model of SNe Ia, including the WD + main sequence (MS) and WD + red giant channels. In the model, the mass-striping effects of optically thick wind and the effects of the thermally unstable disks were included. A model by Hachisu et al, which details how WDs accrete hydrogen-rich material from their companions, was applied to calculate the WD mass growth. Based on the model, Meng & Yang (2010) derived the Galactic birth rate of SNe Ia, which is comparable with that from observations. In this paper, Meng & Yang build on ideas from their earlier paper, Meng and Yang (2010). The purpose of this paper is to present the final parameter space and confirm that the model describes the potential progenitors systems of SNe Ia.
In this paper, researchers show the initial and final state of the progenitor systems of SNe Ia in an orbital-period"“secondary-mass plane for the four cases, namely Case Wind, Case Calm, Case Nova, and Case DNova. In Case Wind, the exploding SNe Ia might be observed like SN 2006X, which shows a variable Na-1D line in its spectra and the others may be normal SNe Ia. Before a supernova explosion, Case Wind may be observed as quasi-regular transient supersoft X-ray sources (SSS) such as V Sagittae. Case Calm might be observed as a persistent SSS and Case Nova as recurrent novae and Case DNova as dwarf nova with recurrent novae.
In the paper also show that the properties of SSS (RX J0513) can be explained by a WD + MS system experiencing stable mass transfer and/or optically thick wind. Its location in the orbital-period"“secondary-mass plane can be explained by both the Case Wind and Case Calm models.
Researchers also present the positions of three recurrent novae: U Sco, V394 CrA, and CI Aql. Based on their position in the orbital-period"“secondary-mass plane, researchers predict that U Sco and V394 CrA are very likely progenitor candidates for SNe Ia. However, CI Aql is also a possible progenitor of SNe Ia, but is less likely. Further observation is still necessary to confirm their companion masses to judge their final fates.
After an SN Ia explosion, the companion star would survive. The supernova ejecta may collide with envelope and strip some hydrogen-rich material from the surface of the companion. The stripped-off hydrogen-rich material may manifest as a narrow hydrogen emission or absorption lines in the spectra of advanced SNe Ia. The amount of the stripped-off material determines whether the narrow hydrogen line can be observed. Analytic study and numerical simulations showed that the lower limit on the quantity of stripped-off material that can be observed is 0.035 solar mass. However, this scenario has not been verified by observations. The use of a reasonable companion structure when simulating the interaction between the supernova ejecta and the companion might be a key factor in overcoming the contradictions between observations and theory. The results in this paper will help to provide constraints on the companion structure, and will guide the study of the interaction between supernova ejecta and companions.
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