**AAS 197, January 2001**

*Session 56. Frontiers of Astrophysics III*

Joint Special Session Oral, Tuesday, January 9, 2001, 10:30am-12:00noon, Town and Country
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## [56.08] On Orbital Elements of Extrasolar Planets and Spectroscopic Binaries: Birds of a Feather

*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

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