Ph.D. candidate GUO Yanjun from Yunnan Observatories of the Chinese Academy of Sciences and her collaborators identified 9,382 early-type stars from the Large Sky Area Multi-Object Fiber Spectroscopy Telescope (LAMOST) medium-resolution survey (LAMOST MRS DR7) and confirmed the relationship of a decreasing trend in binary fractions towards late-type stars.

This work was published in Research in Astronomy and Astrophysics.

Early-type stars are massive and high-temperature stellar objects. Most of the early-type stars exist in binary systems. They are likely to evolve to compact stellar systems. These compact systems are dominant gravitational-wave sources for the laser interferometer gravitational wave observatory (LIGO).

The binary fraction of early-type stars, which determines the birth rate and spatial density distribution of double compact objects, is an important research topic in astronomy.

However, it is difficult to determine the binary fraction for early-type stars due to the absence of an extensive and consistent collection of spectroscopic observations. The million-scale data release from the LAMOST MRS DR7 provides a valuable opportunity to conduct this research.

In this study, the researchers identified 9,382 early-type stars from the LAMOST MRS DR7 database by adopting the technique of measuring the equivalent widths of several spectral lines. The samples are divided into four groups based upon their spectral classifications, i.e., T1 (～O-B4), T2 (～B5), T3 (～B6-B7), and T4 (～B8-A).

They measured the radial velocity of the sample stars and identified spectroscopic binaries for stars displaying significant variations greater than 15.57 km/s. Then they performed a series of Monte-Carlo simulations to correct the observational biases and reported a decreasing trend in binary fractions of target stars towards low temperatures.

They also found that the binary fraction of massive O/B type stars could reach ～70%, while the binary fraction of relatively low-mass B/A stars was about 45%. These results can be further used to constraint the populations of massive binaries and provide insights to trace the formation scenario of compact binaries.