Recently, Ph.D. candidate GUO Yunlang and Prof. WANG Bo, from Yunnan Observatories of the Chinese Academy of Sciences, investigated the formation of Type Ia Supernovae and isolated mildly recycled pulsars through NS+He star donor channel. This work was published in Monthly Notices of the Royal Astronomical Society.

Type Ia supernovae (SNe Ia) are excellent cosmological distance indicators due to their uniform luminosity, revealing the accelerating expansion of the Universe driven by dark energy. They also play an important role in the chemical evolution of galaxies owing to their contributions to the abundance of heavy elements. Although SNe Ia are important objects for cosmology and chemical evolution of galaxies, their progenitors remain controversial.

It is generally believed that SNe Ia are produced by thermonuclear explosions of CO WDs, in which the WDs have masses close to the Chandrasekhar limit (MCh). Two widely studied progenitor models have been proposed to explain the formation of SNe Ia, i.e., the single-degenerate (SD) model and the double-degenerate (DD) model. In the SD model, a CO WD accretes H/He-rich material from a main-sequence star, a red giant star or a He star until thermonuclear explosions occur. In the DD model, two WDs merge in a close binary caused by gravitational wave radiation, and SNe Ia may be produced if their total mass exceeds MCh. Aside from the SD and DD model, some alternative models have been proposed to explain the observed diversity among SNe Ia.

In this study, the researchers calculated the long-term evolution of NS+He star binaries with different initial He star masses and orbital periods for the first time, in which the He star companions can explode as SNe Ia eventually. Their simulations indicate that after the He stars develop highly degenerate oxygen-neon (ONe) cores with masses near the Chandrasekhar limit, explosive oxygen burning can be triggered due to the convective Urca process.

According to these calculations, they obtained an initial parameter space for the production of SNe Ia, which can be used for population synthesis studies. Meanwhile, they found that isolated mildly recycled pulsars can be formed after He stars explode as SNe Ia in NS+He star binaries, in which the isolated pulsars have minimum spin periods of～30-110 ms and final orbital velocities of～60-360 km/s, corresponding to initial orbital periods of～0.07-10 d.

Contact:
GUO Yunlang
Yunnan Observatories, CAS
Email: yunlang@ynao.ac.cn