On orbital elements of extrasolar planetary candidates and spectroscopic binaries

We estimate probability densities of orbital elements, periods and eccentri cities, for the population of extrasolar planetary candidates (EPC) and, se parately, for the population of spectroscopic binaries (SB) with solar-type primaries. We construct empirical cumulative distribution functions (CDFs) in order to infer probability distribution functions (PDFs) for orbital pe riods and eccentricities. We also derive a joint probability density for pe riod-eccentricity pairs in each population. Comparison of respective distri butions reveals that in all cases EPC and SB populations are, in the contex t of orbital elements, indistinguishable from each other to a high degree o f statistical significance. Probability densities of orbital periods in bot h populations have similar toP(-1) functional form, whereas the PDFs of ecc entricities can be best characterized as a Gaussian with a mean of about 0. 35 and standard deviation of about 0.2 turning into a at distribution at sm all values of eccentricity. These remarkable similarities between EPC and S B must be taken into account by theories aimed at explaining the origin of extrasolar planetary candidates, and constitute an important clue as to the ir ultimate nature.