PhD student FANG Xiaohui and Prof. QIAN Shengbang, from Yunnan Observatories of the Chinese Academy of Sciences, confirmed the prediction that the post-nova with orbital periods longer than 3 hours will never hibernate deeply. Monthly Notices of the Royal Astronomical Society have published their research online.

In standard model of cataclysmic variables (CVs) evolution, the dominant angular momentum losses (AMLs) mechanism in long-period system (Porb ＞ 3 hr) is magnetic braking (MB), where short-period CVs (Porb ＜ 2 hr) are assumed to be driven by AMLs associated with the emission of gravitational radiation (GR).

In hibernation scenario, systems after nova outburst will exhibit high mass transfer rates and change themselves into nova-like variables (NLs). The model also predicts that cataclysmic variables (CVs) will experience novae, NLs, and dwarf novae (DNs) in 104 – 105 yr (short for year) and repeat the cycle during their lifetimes.

The orbital periods of NLs usually lay above the period gap (~2 hr), which suggests that they are binaries with mass transfer powered by the removal of angular momentum by magnetic braking.

V1315 Aquila, a nova-like star surrounding by a nova shell due to the nova eruption before 500-1200 yr, is an exemplar for hibernation hypothesis. The effects of mass losses and AMLs after an eruption of V1315 Aquila were investigated by the researchers.

Assuming that the mass transfer is stable, the researchers calculated the mass transfer rate and the effective mass-radius index of the donor stars for NLs with respect to the mass-loss proportion based on their secular orbital period variations. They also calculated their mass-transfer and thermal time-scales.

The researchers found the donors of NLs were unable to maintain thermal equilibrium when compared with the normal CVs under the standard model, and that the mass transfer in V1315 Aquila is unstable due to the irradiation by the white dwarf and the accretion. This is consistent with the predication of the hibernation hypothesis that nova eruptions strongly affect the mass-transfer rate in the binary, and keep it high after a recent nova eruption.

Besides, the researchers estimated its magnitude-decline rate is about 0.1 mmag per year, which is in line with its long-term optical observations. Its time-scale of magnitude decline is comparable to the recurrence time-scale of nova eruption, indicates that V1315 Aquila will not enter into deep hibernation.

This study help understand the nova-induced cycles and hence know more about the CVs evolution.

Contact:

FANG xiaohui, Yunnan Observatories, CAS

fangxiaohui@mail.ynao.ac.cn