Researchers are making progress in the field of classic rising stars

Recently, Guo Yunlang and Wang Bo, phD candidates at the Yunnan Astronomical Observatory of the Chinese Academy of Sciences, have made new progress in the field of classical novae, and the results can be used to limit the mixed theory of white dwarf stars during classical nova explosions. The result was published in the April 2022 issue of the journal Astronomy and Astrophysics (A&A), under the title “Mixing Fraction in Classical Novae.”

Classical novae are thermonuclear reactions that occur on the surface of white dwarfs, which play an important role in the chemical evolution of galaxies and are also candidates for precursor stars of type Ia supernovae. In a close binary system , a white dwarf accretizes material from its companion star through the Roche flap , and once enough material has accumulated on the surface of a white dwarf , it triggers an uncontrolled thermonuclear reaction , forming a nova explosion ( see Figure 1 ) . During a nova explosion, the luminosity increases dramatically, producing enough energy to throw away most of the material that has been accretized. Through the study of nova projectiles, it is possible to understand the characteristics of nova systems, such as the mass of white dwarfs, accretion rates, and the properties of companion stars.

In recent decades, observations have shown that most of the nova projectiles have C, N, O, Ne, Na, Mg, and Al metal enrichment, which indicates that there is a mixture of accretion material and the white dwarf’s own material (that is, white dwarf mixing) during the nova explosion. However, the white dwarf mixing process in nova explosions remains unclear. To this end, the researchers conducted a systematic study of the white dwarf mixture and nova ejecta during the nova explosion, and proposed to use the abundance ratio of the four elements in the ejector to determine the white dwarf mixture during the nova explosion, namely (H + He)/∑ CNO, (H + He)/Ne, ∑ CNO/Mg and ∑ CNO/Si (see Figure 2). The project team found that in nova systems, small-mass white dwarfs lead to high white dwarf mixing.

Figure 1. Schematic diagram of nova explosions in a white dwarf binary system (Image source:

Figure 2. Determination of the mixture of white dwarf stars in new stars, where black pentagrams are observations.

This achievement was supported by the Western Light Cross Team-Key Laboratory Cooperation Project of the Chinese Academy of Sciences and the National Natural Science Foundation of China. (Source: Yunnan Astronomical Observatory, Chinese Academy of Sciences)

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