The envelope mass of red giant donors in type Ia supernova progenitors

Abstract

Context. The single degenerate model is the most widely accepted progenitor model of type Ia supernovae (SNe Ia), in which a carbon-oxygen white dwarf (CO WD) accretes hydrogen-rich material from a main sequence or a slightly evolved star (WD +MS) or from a red giant star (WD + RG), to increase its mass and explodes when approaching the Chandrasekhar mass. The explosion ejecta may impact the envelope of and strip off some hydrogen-rich material from the companion. The stripped-off hydrogen-rich material may manifest itself by means of a hydrogen line in the nebular spectra of SNe Ia. However, no hydrogen line is detected in the nebular spectra. Aims. We compute the remaining amounts of hydrogen in red giant donors to see whether the conflict between theory and observations can be overcome. Methods. By considering the mass-stripping effect from an optically thick wind and the effect of thermally unstable disk, we systematically carried out binary evolution calculation for WD + MS and WD + RG systems. Results. Here, we focus on the evolution of WD + RG systems. We found that some donor stars at the time of the supernova explosion contain little hydrogen-rich material on top of the helium core (as low as 0.017 M ), which is smaller than the upper limit to the amount derived from observations of material stripped-off by explosion ejecta. Thus, no hydrogen line is expected in the nebular spectra of these SN Ia. We also derive the distributions of the envelope mass and the core mass of the companions from WD + RG channel at the moment of a supernova explosion by adopting a binary population synthesis approach. We rarely find a RG companion with a very low-mass envelope. Furthermore, our models imply that the remnant of the WD + RG channel emerging after the supernova explosion is a single low-mass white dwarf (0.15−0.30 M ). Conclusions. The absence of a hydrogen line in nebular spectra of SNe Ia provides support to the proposal that the WD + RG system is the progenitor of SNe Ia.

Subdwarf B stars as possible surviving companions in Type Ia supernova remnants

“…∼ 0.1 − 0.3 M ⊙ , which is much smaller than previous value obtained by numerical simulations (Marietta et al 2000). For the stars in the connection between RG and sdB stars, there envelopes are also very thin, and then even if the envelopes were completely stripped off, it could be difficult to detect them in the nebular spectra of SNe Ia (see also Meng & Yang 2010).…”

“…After the impact of supernova ejecta, the remnant masses of the RG companions and the ones in the connection between RG and sdB stars are close to the minimum mass for the helium ignition in the center of the star (Han et al 2002). If the helium can be ignited in the center of the stars, they may also be sdB stars with a low mass, otherwise luminous helium WDs would be expected in SNRs (Justham et al 2009;Meng & Yang 2010). Figure 6.…”

The companion properties of SNe Ia from the single degenerate model

“…In the SD model, the maximum stable mass of the CO WD is ∼ 1.378M ⊙ (close to the Ch mass limit [7]), and the companion is either a main sequence (or a slightly evolved) star (WD+MS, [10][11][12][13][14]), or a red-giant star (WD+RG, [15]) or a He star (WD + He star, [16]). This scenario is supported by many observations [17] and has been widely studied by many groups [18][19][20][21][22][23][24].…”

The initial and final state of SNe Ia from the single degenerate model

“…However, this scenario has not been verified by observations at present [49,50]. Maybe, a reasonable companion structure used when simulating the interaction between the supernova ejecta and the companion is a key factor to overcome the contradiction between observations and theory [28,51]. Our results in this paper will provide help to constrain the companion structure and are helpful to study the interaction between supernova ejecta and companion.…”

“…Based on the model, [23] derived the Galactic birth rate of SNe Ia, which is comparable with that from observations. In addition, their model may even explain some SNe with low hydrogen mass in explosion ejecta [28]. [23] calculated more than 1600 WD close binary evolution models and showed the initial parameter space leading to SNe Ia in an orbital period -secondary mass (log P i , M i 2 ) plane.…”