Journal
ASTRONOMICAL JOURNAL
Volume 137, Issue 2, Pages 3442-3448Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0004-6256/137/2/3442
Keywords
binaries: spectroscopic; stars: formation; stars: pre-main sequence
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We report an analysis of twins of spectral types F or later in the 9th Catalog of Spectroscopic Binaries (SB9). Twins, the components of binaries with mass ratio within 2% of 1.0, are found among the binaries with primaries of F and G spectral type. They are most prominent among the binaries with periods less than 43 days, a cutoff first identified by Lucy. Within the subsample of binaries with P < 43 days, the twins do not differ from the other binaries in their distributions of periods (median P similar to 7 days), masses, or orbital eccentricities. Combining the mass-ratio distribution in the SB9 in the mass range 0.6-0.85 M(circle dot) with that measured by Mazeh et al. for binaries in the Carney-Latham high proper motion survey, we estimate that the frequency of twins in a large sample of spectroscopic binaries is about 3%. Current theoretical understanding indicates that accretion of high specific angular momentum material by a protobinary tends to equalize its masses. We speculate that the excess of twins is produced in those star-forming regions where the accretion processes were able to proceed to completion for a minority of protobinaries. This predicts that the components of a young twin may appear to differ in age and that, in a sample of spectroscopic binaries in a star formation region, the twins are, on average, older than the binaries with mass ratios much smaller than 1.
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