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Astron. Astrophys. 356, 903-912 (2000)

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Statistics of low-mass companions to stars: Implications for their origin

T.F. Stepinski and D.C. Black

Lunar and Planetary Institute, 3600 Bay Area Blvd., Houston, TX 77058, USA (tom@lpis54.jsc.nasa.gov)

Received 31 August 1999 / Accepted 17 February 2000


One of the more significant results from observational astronomy over the past few years has been the detection, primarily via radial velocity studies, of low-mass companions (LMCs) to solar-like stars. The commonly held interpretation of these is that the majority are "extrasolar planets" whereas the rest are brown dwarfs, the distinction made on the basis of apparent discontinuity in the distribution of [FORMULA] for LMCs as revealed by a histogram. We report here results from statistical analysis of [FORMULA], as well as of the orbital elements data for available LMCs, to test the assertion that the LMCs population is heterogeneous. The outcome is mixed. Solely on the basis of the distribution of [FORMULA] a heterogeneous model is preferable, although no unique best-fit mixture can be determined. On the basis of the distribution of orbital periods and eccentricities a homogeneous model is strongly preferable. Overall, we find that a definitive statement asserting that LMCs population is heterogeneous is, at present, unjustified. In addition we compare statistics of LMCs with a compatible sample of stellar binaries. We find a remarkable statistical similarity between these two populations. This similarity coupled with marked populational dissimilarity between LMCs and acknowledged planets motivates us to suggest a common origin hypothesis for LMCs and stellar binaries as an alternative to the prevailing interpretation. We discuss merits of such a hypothesis and indicate a possible scenario for the formation of LMCs.

Key words: stars: binaries: spectroscopic – stars: formation – stars: low-mass, brown dwarfs – stars: planetary systems – stars: statistics

Send offprint requests to: T. Stepinski

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© European Southern Observatory (ESO) 2000

Online publication: April 17, 2000