Q(alpha) reconsidered
1978; self-publishing; Volume: 98; Issue: 1025 Linguagem: Inglês
ISSN
0029-7704
Autores Tópico(s)Astro and Planetary Science
Resumo1978 August q(a) Reconsidered 163 References . S. Webster & M. Ryle, M.N., I75, 95, I976. . P. Kirshner, P.A.S.P., 88, 585, 1976. ( ) B. Elsmore & M. Ryle, M.N., 174, 411, 1976. (4) R. W. Hunstead, M.N., I52, 277, I971. ( ) L. Helmer & H. J. Fogh Olsen, A. 69’ A. Suppl., 30, 866, I977. q(a) RECONSIDERED By Virginia T rimble University of California, Irvine, and University of Maryland The distribution of mass ratios in spectroscopic binaries, q(a), has been brought up to date and plotted in a slightly more sensible way. All features of the previous determination persist. The most important of these is bimodality: q(a) has peaks near M2/M1 = o-2-0-3 and o-9-1-o. Every subsam le, including unevolved systems, also displays this double-pe ed distribution function. It probably implies that binaries are formed by two mechanisms, acting like fission and capture. The problem of whether the binary stars comprise one, two, or more populations is sufliciently ancient to be considered honourablel. It can be tackled theoretically by asking how many different ways one can think of for binaries to form and subsequently evolve. The answers range from zero to many, depending on how rigorous one requires the mathematics to be. Advertised formation mechanisms include fission of a single proto-star, capture of one pre—existing star by another, and separate condensation of two proto-stars which later find themselves to be gravitationally bound. The inevitability of transfer of gas from one star to the other in, at least, close systems, forces one to recognize an evolved and an unevolved population even if there is only one formation mechanism. The problem can also be tackled observationally by asking how various properties of binaries (separation, period, orbital eccentricity, total mass, mass ratio, orbit orientation) are distributed among known systems. Provided that the available observations are not dominated by selection effects, a single population should show up as a unimodal distribution in the various properties, while multiple populations could produce more complex distri- bution functions. Of the distributions that have been studied, that of periastron angle is thought to be dominated by selection effects and that of eccentricity by tidal evolution of the orbits2. One study of separations (of binaries in OB associations)“ found a bimodal distribution. Others1»5, looking at field stars, found a single peak near 20 AU when both visual and spectroscopic systems were included. The period distributions for field B2—5 and F3—G2 IV—V binaries“-7 similarly have single peaks, occurring at periods of several years, when spectroscopic, visual, and common proper motion pairs are all included. © The Observatory 0 Provided by the NASA Astrophysics Data System
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