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D.C. Black, T.F. Stepinski (Lunar & Planetary Institute)
We estimate probability densities of orbital elements, periods and eccentricities, for the population of extrasolar planets (EPs) and, separately, for the population of spectroscopic binaries (SB) with solar-type primaries. We construct empirical cumulative distribution functions (CDFs) and use them to estimate probability distribution functions (PDFs) for orbital periods and eccentricities. We also derive bivariate PDFs for period-eccentricity pairs in each population. Our overall conclusion is that, in the context of orbital elements, EP and SB populations are indistinguishable from each other. Probability densities of orbital periods (P) in both populations have ~1/P functional form, whereas the PDFs of eccentricities can be best characterized as a gaussian with the mean of about 0.35 and the standard deviation of about 0.2 appended by a flat distribution at small values of eccentricity. These remarkable similarities between EP and SB, particularly in light of recent findings from astrometric studies of the parent stars to "extrasolar planets" (Gatewood et al. 2000, Han et al. 2000) constitute both an important clue to, and a strong constraint on, the true nature of these companions. This work is support by NASA through contract No. NASW-4574.
The author(s) of this abstract have provided an email address for comments about the abstract: Black@lpi.usra.edu