2006A&A...457..629L

The assertion that there is an intrinsic excess of binaries with mass ratios q≃1 - the twin hypothesis - is investigated. A strong version of this hypothesis (H_s), due to Lucy & Ricco (1979AJ.....84..401L) and Tokovinin (2000A&A...360..997T), refers to a narrow peak in the distribution function ψ(q) for q>0.95. A weak version (H_w), due to Halbwachs et al. (2003A&A...397..159H), refers to a broad peak for q>0.8. Current data on SB2's is analysed and H_s is found to be statistically significant for a sample restricted to orbits of high precision. But claims that H_s is significant for binaries with special characteristics are not confirmed since the sample sizes are well below the minimum required for a reliable test. With regard to H_w, additional observational evidence is not presented, but evidence to the contrary in the form of Hogeveen's (1992Ap&SS.196..299H) model of biased sampling with ψ∝q^–2 is criticized. Specifically, his success in thus fitting catalogued data depends on implausible assumptions about the research methodologies of binary-star spectroscopists.