**DPS 2001 meeting, November 2001**

*Session 40. Extra-Solar Planet Posters*

Displayed, 9:00am Tuesday - 3:00pm Saturday, Highlighted, Friday, November 30, 2001, 9:00-10:30am, French Market Exhibit Hall
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## [40.04] Stability of a Planet in a Binary System: MACHO-97-BLG-41 Planetary System

*K. Moriwaki, Y. Nakagawa (Kobe University)*

We estimate upper limits of binary and planetary
eccentricities in the extrasolar planetary system,
MACHO-97-BLG-41 lens system. This planet was detected by
gravitational microlensing, and is considered to be the
first observed one orbiting both components of the binary
star system. This observational technique cannot determine
binary and planetary eccentricities. However, these orbital
elements may be estimated by long-term numerical
integrations of binary and planetary orbital motions. We
performed such long-term numerical integrations with various
initial conditions in order to see what initial
configuration produces the stable planetary orbits during
the integration (10^{6} binary periods or approximately
2.8Myr). The numerical results show that the upper limit of
binary eccentricity for stable planetary orbit in this
system is about 0.5 under the assumption of the initial
circular orbit of the planet. In the case of initial
elliptic orbit of planet, we have found a tendency that
planetary orbital motion become unstable in shorter
time-scale and the upper limit of binary eccentricity
decreases with increasing initial planetary eccentricity.
The numerical results show that the upper limit of the
initial planetary eccentricity is about 0.3 for stable
planetary orbits. More over, we tried numerical integrations
in the case of retrograde orbit, and found that the
planetary retrograde orbit is more stable than the prograde
case.

The author(s) of this abstract have provided an email address
for comments about the abstract:
moriwaki@jet.planet.sci.kobe-u.ac.jp

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