Planets in habitable zones:

Free access article

Issue		A&A Volume 398, Number 1, January IV 2003


Page(s)		L1 - L4
Section		Letters
DOI		http://dx.doi.org/10.1051/0004-6361:20021805

A&A 398, L1-L4 (2003)
DOI: 10.1051/0004-6361:20021805

Letter

A study of the binary Gamma Cephei

R. Dvorak, E. Pilat-Lohinger, B. Funk and F. Freistetter

Institute for Astronomy, University of Vienna, Türkenschanzstrasse 17, 1180 Vienna, Austria
(Received 13 November 2002 / Accepted 5 December 2002)

Abstract
The recently discovered planetary system in the binary $\gamma$ Cep was studied concerning its dynamical evolution. We confirm that the orbital parameters found by the observers are in a stable configuration. The primary aim of this study was to find stable planetary orbits in a habitable region in this system, which consists of a double star ( a=21.36 AU) and a relatively close ( a=2.15 AU) massive ( $1.7~m_{\rm jup}\sin i$ ) planet. We did straightforward numerical integrations of the equations of motion in different dynamical models and determined the stability regions for a fictitious massless planet in the interval of the semimajor axis $0.5~{\rm AU} < a <1.85~{\rm AU}$ around the more massive primary. To confirm the results we used the Fast Lyapunov Indicators (FLI) in separate computations, which are a common tool for determining the chaoticity of an orbit. Both results are in good agreement and unveiled a small island of stable motions close to 1 AU up to an inclination of about $15^\circ$ (which corresponds to the 3:1 mean motion resonance between the two planets). Additionally we computed the orbits of earthlike planets (up to 90 earthmasses) in the small stable island and found out, that there exists a small window of stable orbits on the inner edge of the habitable zone in $\gamma$ Cep even for massive planets.

Key words: stars: individual: $\gamma$ Cep -- stars: planetary systems -- habitable zones

Offprint request: R. Dvorak, dvorak@astro.univie.ac.at

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