Astronomy & Astrophysics

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Issue		A&A Volume 410, Number 2, November I 2003
Page(s)		L13 - L16
Section		Letters
DOI		10.1051/0004-6361:20031404

A&A 410, L13-L16 (2003)
DOI: 10.1051/0004-6361:20031404

Letter

A study of the stable regions in the planetary system HD 74156 - Can it host earthlike planets in habitable zones?

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

Institute for Astronomy, University of Vienna, Türkenschanzstrasse 17, 1180 Vienna, Austria
(Received 2 July 2003 / Accepted 11 September 2003)

Abstract
Using numerical methods we thoroughly investigate dynamical stability in the region between the two planets found in HD 74156. The two planets with semimajor axes 0.28 AU and 3.82 AU move on quite eccentric orbits ( e=0.649 and 0.354). There is a region between 0.7 and 1.4 AU which may host additional planets which we checked via numerical integrations for different dynamical models. Besides the orbital evolution of several thousands of massless planets in a three-dimensional restricted 4-body problem (host star, two planets + massless bodies) we also have undertaken test computations of the orbital evolution of fictitious planets with masses of 0.1, 0.3 and 1 $M_{{\rm JUP}}$ in the region between HD 74156b and HD 74156c. For direct numerical integrations up to 10⁷ years we used the Lie-integrator, a method with adaptive step-size. We also computed the Fast Lyapunov Indicators to detect chaotic motion in this region. We emphasize the important rôle of the inner resonances (with the outer planet) and outer resonances (with the inner planet) with test bodies located inside the resonances. In these two "resonance" regions almost no orbits survive. The region between the 1:5 outer resonance (0.8 AU) and the 5:1 inner resonance (1.3 AU), just in the right position for habitability, is also not very likely to host planets. Our results do not strictly "forbid" planets to move in the habitable zone, but their existence is unlikely.

Key words: stars: individual: HD 74156 -- stars: planetary systems -- habitable zones

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

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