Mass Ratio Distribution of Hierarchical Triple Systems from the LAMOST-MRS Survey

Abstract

Hierarchical triple-star systems consists of three components organized into an inner binary (M 1, M 2) and a more distant outer tertiary (M 3) star. The LAMOST Medium-Resolution Spectroscopic Survey has offered a great sample for the study of triple-system populations. We used the peak amplitude ratio method to obtain the mass ratio (q in, q out) of a triple system from its normalized spectrum. By calculating the cross-correlation function, we determined the correlation between the mass ratio q out (M 3/(M 1 + M 2)) and the amplitude ratio (A 3/(A 1 + A 2)). We derived a q in of 0.5–1.0 and a q out between 0.2 and 0.8. By fitting a power-law function of the corrected q in distribution, γ in is estimated to be −0.654 ± 2.915, 4.304 ± 1.125, and 11.371 ± 1.309 for A-, F-, and G-type stars. The derived γ in values increase as the mass decreases, indicating that less massive stars are more likely to have companion stars with similar masses. By fitting a power-law function of the corrected q out distribution, γ out is estimated to be −2.016 ± 0.172, −1.962 ± 0.853, and −1.238 ± 0.141 for G-, F-, and A-type stars, respectively. The γ out values show a trend of growth toward lower primary star masses.