The majority of what we know about the universe comes from star studies, and roughly half of the stars are discovered to be in binary systems. The close binary interaction between the stellar components may alter the stars’ fate.
A team of researchers from the Chinese Academy of Sciences’ Yunnan Observatories devised a novel method for investigating the mass-ratio distribution of binary stars identified by the Large Sky Area Multi-Object Fiber Spectroscopy Telescope using the medium-resolution Survey Telescope (LAMOST-MRS). The mass-ratio distribution and binary fractions are important for studying binary formation and evolution.
On July 8, this work was published in The Astrophysical Journal.
Binarity is very common in stars. Massive stars have a binary fraction of up to 70%, while solar-type stars have a binary fraction of only 44%. Such evidence suggests that the binary fraction plays a significant role in the binary population.
Type Ia supernovae, double black holes, double neutron stars, millisecond pulsars, and X-ray binaries are examples of stellar objects that may form as a result of binary evolution. The compact systems contribute to the chemical evolution of galaxies and provide early universe re-ionizing photons.
Binary population observational properties are critical for understanding binary evolution. These include the binary fraction, binary orbital period distribution, mass-ratio distribution, and distribution dependence on stellar spectral type and metallicity. Due to the lack of a large and consistent sample, the statistical properties of the binary population are poorly understood.
However, thanks to the large sample of spectroscopic observations obtained from the LAMOST-MRS, which allows the researchers to investigate the properties of mass-ration distribution and binary fraction, this situation has drastically changed.
The researchers developed a peak amplitude ratio (PAR) method to calculate the mass ratio of double-lined spectroscopic binaries found in the LAMOST-MRS survey. When two peaks appeared in the cross-correlation functions, a system was identified as a double-lined spectroscopic binaries (SB2) system based on the different radial velocities measured from the component stars in a binary system (CCFs). The PAR of the CCF peaks may be affected by the binary system’s mass ratio.
The researchers used the spectral observations obtained from the LAMOST-MRS Data Releases 6 and 7 to form distributions of the derived mass ratio of the binary systems to their spectral types (including A-, F-, and G-type). The researchers discovered that G-type stars are more likely to be discovered as twins.