Are the majority of sun-like stars single?

Abstract

It has recently been suggested that, in the field,~56 per cent of Sun-like stars (0.8M⊙ ≲ M≲ ≲ 1.2M⊙) are single.We argue here that this suggestion may be incorrect, since it appears to be based on the multiplicity frequency of systems with Sun-like primaries, and therefore takes no account of Sun-like stars that are secondary (or higher order) components in multiple systems. When these components are included in the reckoning, it seems likely that only ~46 per cent of Sun-like stars are single. This estimate is based on a model in which the system mass function has the form proposed by Chabrier, with a power-law Salpeter extension to high masses; there is a flat distribution of mass ratios; and the probability that a system of mass M is a binary is 0.50 + 0.46 log10(M/M⊙) for 0.08M⊙ ≤ M ≤ 12.5M⊙, 0 for M < 0.08M⊙, and 1 for M > 12.5M⊙. The constants in this last relation are chosen so that the model also reproduces the observed variation of multiplicity frequency with primary mass. However, the more qualitative conclusion, that a minority of Sun-like stars are single, holds up for virtually all reasonable values of the model parameters. Parenthetically, it is still likely that the majority of all stars in the field are single, but that is because most M Dwarfs probably are single.