Mass-Ratio Distribution of Binaries From the LAMOST-MRS Survey

Abstract

Binary evolution leads to the formation of important objects crucial to the development of astrophysics, but the statistical properties of binary populations are still poorly understood. The LAMOST-MRS has provided a large sample of stars to study the properties of binary populations, especially for the mass ratio distributions and the binary fractions. We have devised a Peak Amplitude Ratio (PAR) approach to derive the mass ratio of a binary system based on results obtained from its spectrum. By computing a cross-correlation function (CCF), we established a relationship between the derived mass ratio and the PARs of the binary systems. By utilizing spectral observations obtained from LAMSOT DR6 & DR7, we applied the PAR approach to form distributions of the derived mass ratio of the binary systems to the spectral types. We selected the mass ratio within the range of $0.6-1.0$ for investigating the mass-ratio distribution. Through a power-law fitting, we obtained the power index $\gamma$ values of $-0.42\pm 0.27$, $0.03\pm 0.12$, and $2.12\pm 0.19$ for A-, F-, and G-type stars identified in the sample, respectively. The derived $\gamma$-values display an increasing trend toward lower primary star masses, and G-type binaries tend to be more in twins. The close binary fractions (for $P\lesssim 150\mathrm{d}$ and $q\gtrsim 0.6$) in our sample for A, F and G binaries are $7.6\pm 0.5\%$, $4.9\pm 0.2\%$ and $3.7\pm 0.1\%$, respectively. Note that the PAR approach can be applied to large spectroscopic surveys of stars.

18 pages, 12 figures, accepted for publication in The Astrophysical Journal

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