分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Some surviving companions of type Ia supernovae (SNe Ia) from the white-dwarf + main-sequence (WD + MS) channel may evolve to hot subdwarfs. In this paper, we preformed stellar evolution calculations for surviving companions of close WD + MS systems in the spin-up/spin-down model and the canonical non-rotating model to map out the initial parameter spaces in the orbital period - secondary mass plane in which the surviving companions can evolve to hot subdwarfs. Based on these results, we carried out a series of binary population synthesis calculation to obtain the Galactic birth rate of the hot subdwarfs from the WD + MS channel, which is $2.3-6\times10^{\rm -4}\,{\rm yr}^{\rm -1}$ for the spin-up/spin-down model and $0.7-3\times10^{\rm -4}\,{\rm yr}^{\rm -1}$ for the canonical non-rotating model. We also show the distributions of some integral properties of the hot subdwarfs, e.g. the mass and the space velocity, for different models. In addition, comparing our results with the observations of the intermediate helium-rich (iHe-rich) hot subdwarfs, the hot subdwarfs from the WD + MS channel may explain some observational features of the iHe-rich hot subdwarfs, especially for those from the spin-up/spin-down model. Although we expect that the SN Ia channel can only contribute a small fraction of the iHe-rich hot subdwarf population, some of these may help to explain cases with unusual kinematics.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The single-degenerate (SD) model is one of the leading models for the progenitors of Type Ia supernovae (SNe Ia). Recently, a new version of the SD model, the common-envelope wind (CEW) model, has been proposed, which, in principle, has the potential to resolve most of the difficulties encountered by previous SD models. This model is still being developed and a number of open issues remain, such as the details of the mass-loss mechanism from the surface of the common envelope (CE), the main observational properties, and the spiral-in timescale of the binary inside the envelope. In this article, we aim to address these issues by considering hydrodynamical effects on the CE. Using the stellar evolution code MESA, we carried out a series of 1D hydrodynamical simulations of an asymptotic giant branch (AGB) star undergoing a common-envelope phase with different envelope masses (0.0007-0.06 solar mass). We found that the envelopes are always dynamically unstable, leading to regular mass ejection events if the envelope is more massive than the critical value of ~ 0.003 solar mass. The kappa mechanism can naturally explain this phenomenon. We also found that, due to the low mass of the CE, the estimated frictional luminosity caused by the spiral-in of the immersed binary is much less than the nuclear luminosity, and therefore will not affect the structure of the CE significantly. Our results imply that the CE in the CEW model cannot be very massive. We also present a rough estimate for the spiral-in timescale based on a simplified model. We found that, for reasonable assumptions, the timescale may be longer than a few 100,000 yr; therefore, the white dwarf may have enough time to increase its mass toward the Chandrasekhar mass, avoiding a merger with the companion.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The single-degenerate (SD) model is one of the leading models for the progenitors of Type Ia supernovae (SNe Ia). Recently, a new version of the SD model, the common-envelope wind (CEW) model, has been proposed, which, in principle, has the potential to resolve most of the difficulties encountered by previous SD models. This model is still being developed and a number of open issues remain, such as the details of the mass-loss mechanism from the surface of the common envelope (CE), the main observational properties, and the spiral-in timescale of the binary inside the envelope. In this article, we aim to address these issues by considering hydrodynamical effects on the CE. Using the stellar evolution code MESA, we carried out a series of 1D hydrodynamical simulations of an asymptotic giant branch (AGB) star undergoing a common-envelope phase with different envelope masses (0.0007-0.06 solar mass). We found that the envelopes are always dynamically unstable, leading to regular mass ejection events if the envelope is more massive than the critical value of ~ 0.003 solar mass. The kappa mechanism can naturally explain this phenomenon. We also found that, due to the low mass of the CE, the estimated frictional luminosity caused by the spiral-in of the immersed binary is much less than the nuclear luminosity, and therefore will not affect the structure of the CE significantly. Our results imply that the CE in the CEW model cannot be very massive. We also present a rough estimate for the spiral-in timescale based on a simplified model. We found that, for reasonable assumptions, the timescale may be longer than a few 100,000 yr; therefore, the white dwarf may have enough time to increase its mass toward the Chandrasekhar mass, avoiding a merger with the companion.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Supersoft X-ray sources (SSSs) are known as possible progenitors of Type Ia supernovae. The quasi-periodic variability has been detected in the optical light curves of SSSs. However, the exact origin of such quasi-periodic observable features remains a mystery. In this paper, we aim to reproduce the observed optical quasi-periodic variability of SSSs by proposing a white dwarf (WD) accretion model with a periodic mass transfer caused by the irradiation of supersoft X-ray onto the companion star. Methods. Assuming that a periodic mass transfer from the companion star to the WD can be caused while the supersoft X-ray irradiates the companion star, we used MESA to simulate the WD accretion process and the subsequent WD evolution by adopting a periodic jagged accretion rate. Comparing our results to the optical light curves of a well-observed SSS RX J0513.9-6951, we find that our models can reproduce the quasi-periodic transition between the optical high and low states of RX J0513.9-6951 because the periodic accretion rate can lead to the WD photosphere expands and contracts periodically in our models. In addition, we find that the transitional periods of the SSSs in our models strongly depend on the mass of the accreting WDs. The more massive the WD mass is, the shorter the transitional period. Based on our results, we suggest that the periodic mass transfer caused by the irradiation of supersoft X-ray onto the companion star may be the origin of the observed optical quasi-periodic variability in SSSs. In addition, our results indicate that the observed optical transition period of a SSS may be useful for the rough estimate of the mass of an accreting WD.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Recent studies have suggested that type Iax supernovae (SNe Iax) are likely to result from a weak deflagration explosion of a Chandrasekhar-mass white dwarf in a binary system with a helium (He)-star companion. Assuming that most SNe Iax are produced from this scenario, in this work we extend our previous work on the three-dimensional hydrodynamical simulation of ejecta-companion interaction by taking the orbital and spin velocities of the progenitor system into account. We then follow the post-impact evolution of a surviving He-star companion by using the one-dimensional stellar evolution code \textsc{MESA}. We aim to investigate the post-explosion rotation properties of a He-star companion in SNe Iax. We find that the He-star companion spins down after the impact due to the angular-momentum loss and expansion caused by the mass-stripping and shock heating during the interaction. This leads to the situation where the surface rotational speed of the surviving companion can drop to one-third of its pre-explosion value when it expands to a maximum radius a few years after the impact. Subsequently, the star shrinks and spins up again once the deposited energy is released. This spin-switching feature of the surviving He-star companions of SNe Iax may be useful for the identification of such objects in future observations.
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