SETI public: High Orbital Eccentricities of Extrasolar Planets Induced by the Kozai Mechanism

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Astrophysics, abstract
astro-ph/0502404
From: Genya Takeda [view email]
Date (v1): Mon, 21 Feb 2005 10:36:24 GMT (55kb)
Date (revised v2): Thu, 9 Jun 2005 22:53:11 GMT (56kb)

High Orbital Eccentricities of Extrasolar Planets Induced by the Kozai
Mechanism

Authors: G. Takeda, F.A. Rasio (Northwestern University)
Comments: 24 pages, 6 figures, ApJ, in press, minor changes to reflect the
accepted version

One of the most remarkable properties of extrasolar planets is their high
orbital eccentricities. Observations have shown that at least 20% of these
planets, including some with particularly high eccentricities, are orbiting
a component of a wide binary star system. The presence of a distant binary
companion can cause significant secular perturbations to the orbit of a
planet. In particular, at high relative inclinations, a planet can undergo a
large-amplitude eccentricity oscillation. This so-called "Kozai mechanism"
is effective at a very long range, and its amplitude is purely dependent on
the relative orbital inclination. In this paper, we address the following
simple question: assuming that every host star with a detected giant planet
also has a (possibly unseen, e.g., substellar) distant companion, with
reasonable distributions of orbital parameters and masses, how well could
secular perturbations reproduce the observed eccentricity distribution of
planets? Our calculations show that the Kozai mechanism consistently
produces an excess of planets with very high (e >0.6) and very low (e < 0.1)
eccentricities. The paucity of near-circular orbits in the observed sample
cannot be explained solely by the Kozai mechanism, because, even with high
enough inclinations, the Kozai mechanism often fails to produce significant
eccentricity perturbations when there are other competing sources of orbital
perturbations on secular timescales, such as general relativity. On the
other hand, the Kozai mechanism can produce many highly eccentric orbits.
Indeed the overproduction of high eccentricities observed in our models
could be combined with plausible circularizing mechanisms (e.g., friction
from residual gas) to create more intermediate eccentricities (e=0.1-0.6).

http://arxiv.org/abs/astro-ph/0502404

• Previous message: LARRY KLAES: "SETI public: Lectures on High-Energy Neutrino Astronomy"

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