Ph.D. candidate GUO Yanjun, from Yunnan Observatories of the Chinese Academy of Sciences, and her collaborators reported a recent work on identifying 9,382 early-type stars from the Large Sky Area Multi-Object Fiber Spectroscopy Telescope (LAMOST) medium-resolution survey (LAMOST MRS DR7) and confirming 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. And they are likely evolving to compact stellar systems, such as double black holes, double neutron stars and neutron star-black hole 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. Motivated by the million-scale data release from the LAMOST MRS DR7, such a database provides a valuable opportunity to conduct this research.

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). The researchers measured the radial velocity of the sample stars and identified spectroscopic binaries for stars displaying significant variations greater than 15.57 km/s. Then researchers 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.

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

Contact:

GUO Yanjun, Yunnan Observatories, CAS

guoyanjun@ynao.ac.cn