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Multiplicity of Solar-Type Stars*

  • Helmut A. Abt (a1)

Abstract

A systematic search for binaries in a sample of 123 bright field stars of types F3-G2 IV or V is described. Combination of the results for 25 newly discovered spectroscopic binaries with those of 21 spectroscopic, 23 visual, and 25 common-proper-motion pairs previously known brings to 88 the total number of companions identified in the sample. The distribution of the 88 periods shows a single maximum; the median period is 14 years.

The frequencies of singles: doubles: triples: quadruples are found to be 42: 46: 9: 2. Less than half of the stars are thus observed to be single. Estimates of the completeness of this search lead to a determination of the number of systems missed and to a determination of their secondary masses.

Analysis of the secondary-mass distributions, observed and predicted from completeness estimates, indicates the existence of two types of binaries.

For systems with periods less than about 100 years, the distribution of secondaries varies with the cube-root of the secondary mass. These systems must be the result of fission. Two-thirds of their primaries have companions of stellar mass. Extrapolation of the cube-root relation implies that the remaining one-third of the primaries have non-stellar secondaries, i.e., close companions whose masses are less than 0.07 solar masses.

For systems with periods larger than roughly 100 years the distribution of secondaries follows that given by the van Rhijn function. They must be the result of condensations that contracted separately but are bound gravitationally. Roughly three-fourths of all primaries in the sample have such distant companions, all of which are likely to be themselves close fission-systems. Evidently single stars are rare among solar-type dwarfs.

Resumen

Se describe una búsqueda sistemática de binarias en una muestra de 123 estrellas brillantes de campo, de tipos F3-G2 IV o V. Combinando los resultados de 25 nuevas binarias espectroscópicas con los de 21 binarias espectroscópicas, 23 binarias visuales y 25 pares de movimiento propio común, previamente conocidas, llega a 88 el número total de compañeras identificadas en esta muestra. La distribución de los 88 períodos muestra un máximo único. El periodo medio es de 14 años. Las frecuencias de estrellas solas, dobles, triples o cuádruples se ha encontrado que es 42, 46, 9 y 2 por lo tanto menos de la mitad de las estrellas son solas. Estimaciones de la complétez de esta búsqueda condujeron a una determinación del número de los sistemas que no son detectados así como a una determinación de las masas de sus secundarias.

Un análisis de la distribución de masas secundarias observadas y predichas de las estimaciones de complétez indica la existencia de dos tipos de binarias:

Para sistemas con periodos menores de aproximadamente 100 años, la distribución de las secundarias varía con la raíz cúbica de la masa de la secundaria. Estos sistemas deben ser resultado de fisión. Dos terceras partes de sus primarias tienen compañeras de masa estelar. La extrapolación de la relación de la raíz cúbica implica que el tercio restante de las primarias tienen secundarias de masa no estelar, i.e., compañeras cercanas cuyas masas son menores que 0.07 masas solares.

Para sistemas con periodos mayores de aproximadamente 100 años la distribución de las secundarias sigue la función dada por van Rhijn. Estos sistemas deben ser el resultado de condensaciones que se contrajeron separadamente pero que están amarradas gravitacionalmente. A grosso modo, tres cuartos de todas las primarias en la muestra tienen tales compañeras distantes, todas éstas a su vez pueden ser sistemas cerrados formados por fisión. Evidentemente las estrellas únicas son raras entre las enanas de tipo solar.

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Copyright

Footnotes

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*

Figures 1 and 2 have been reproduced from Ap. J. Suppl. Ser., 1976, 30, 273, published by the University of Chicago Press for the American Astronomical Society.

Footnotes

References

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Abt, H. A. 1961, Ap. J. Suppl., 6, 37.
Abt, H. A., and Levy, S. G. 1976, Ap. J. Suppl., 30, 273.
Abt, H. A., and Snowden, M. S. 1973, Ap. J. Suppl., 25, 137.
Goldreich, P., and Ward, W. R. 1973, Ap. J., 183, 1051.
Kuiper, G. P. 1935, Pub. A.S.P., 47, 15 and 121.
Luyten, W. J. 1930, Proc. Natl. Acad. Sci., 16, 257.

Multiplicity of Solar-Type Stars*

  • Helmut A. Abt (a1)

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