Trojan pairs in the HD 128311 and HD 82943 planetary systems?

Two nearby stars, HD 128311 and HD 82943, are believed to host pairs of Jupiter-like planets involved in a strong first order 2:1 mean motion resonance (MMR). In this work we reanalyze available radial velocity (RV) measurements and demonstrate that it is also possible to explain the observed RV variations of the parents stars as being induced by a pair of Trojan planets (i.e., in a 1:1 MMR). We show that these Trojan configurations reside in extended zones of stability in which such systems may easily survive in spite of large masses of the planets, large eccentricities and nonzero mutual inclinations of their orbits. We also show that HD 82943 could harbor a previously unknown third planet about of 0.5 Jupiter masses in 2.1 AU orbit.Comment: 18 pages (total), 17 figures in low resolution format suitable for arXiv, revised version resubmitted to ApJ. The preprint with high resolution images is available from http://www.astri.uni.torun.pl/~chris/astroph.0510109v2.ps.g

The Janus head of the HD 12661 planetary system

In this work we perform a global analysis of the radial velocity curve of the HD 12661 system. Orbital fits that are obtained by the genetic and gradient algorithms of minimization reveal the proximity of the system to the 6:1 mean motion resonance. The orbits are locked in the secular resonance with apsidal axes librating about 180 deg with the full amplitude $\simeq (90,180) deg$. Our solution incorporates the mutual interaction between the companions. The stability analysis with the MEGNO fast indicator shows that the system is located in an extended stable zone of quasi-periodic motions. These results are different from those obtained on the basis of the orbital fit published by Fischer et al. (2003)Comment: 7 pages, 5 figures, manuscript submitted to ApJ Letters, revised versio

About putative Neptune-like extrasolar planetary candidates

We re-analyze the precision radial velocity (RV) data of HD188015, HD114729, HD190360, HD147513 and HD208487. All these stars are supposed to host Jovian companions in long-period orbits. We test a hypothesis that the residuals of the 1-planet model of the RV or an irregular scatter of the measurements about the synthetic RV curve may be explained by the existence of additional planets in short-period orbits. We perform a global search for the best fits in the orbital parameters space with genetic algorithms and simplex method. This makes it possible to verify and extend the results obtained with an application of commonly used FFT-based periodogram analysis for identifying the leading periods. Our analysis confirms the presence of a periodic component in the RV data of HD190360 which may correspond to a hot-Neptune planet. We found four new cases when the 2-planet model yields significantly better fits to the RV data than the best 1-planet solutions. If the periodic variability of the residuals of single-planet fits has indeed a planetary origin then hot-Neptune planets may exist in these extrasolar systems. We estimate their orbital periods in the range of 7-20d and minimal masses about of 20 masses od the Earth.Comment: Contains 14 pages, 24 figures, 1 table. Accepted for publication in Astronomy and Astrophysics (4/11/2005). This is a raw unedited manuscript. Some figures are in low-resolution format suitable for publication in astro-p

Orbital configurations and dynamical stability of multi-planet systems around Sun-like stars HD 202206, 14 Her, HD 37124 and HD 108874

We perform a dynamical analysis of the recently published radial velocity (RV) measurements of a few solar type stars which host multiple Jupiter-like planets. In particular, we re-analyze the data for HD 202206, 14 Her, HD 37124 and HD 108874. We derive dynamically stable configurations which reproduce the observed RV signals using our method called GAMP (an acronym of the Genetic Algorithm with MEGNO Penalty). The GAMP relies on the N-body dynamics and makes use of genetic algorithms merged with a stability criterion. For this purpose, we use the maximal Lyapunov exponent computed with the dynamical fast indicator MEGNO. Through a dynamical analysis of the phase-space in a neighborhood of the obtained best-fit solutions, we derive meaningful limits on the parameters of the planets. We demonstrate that GAMP is especially well suited for the analysis of the RV data which only partially cover the longest orbital period and/or correspond to multi-planet configurations involved in low-order mean motion resonances (MMRs). In particular, our analysis reveals a presence of a second Jupiter-like planet in the 14 Her system (14 Her c) involved in a 3:1 or 6:1 MMR with the known companion b. We also show that the dynamics of the HD 202206 system may be qualitatively different when coplanar and mutually-inclined orbits of the companions are considered. We demonstrate that the two outer planets in the HD 37124 system may reside in a close neighborhood of the 5:2 MMR. Finally, we found a clear indication that the HD 108874 system may be very close to, or locked in an exact 4:1 MMR.Comment: Contains 7 pages (text), 17 figures (some in low resolution suitable for astro-ph), 1 table. Submitted to ApJ. The manuscript with high-resolution figures is available from http://www.astri.uni.torun.pl/~chris/ms64109.ps.g

The exosystems about HD169830 and HD12661: are they dynamical twins?

The new 2-planetary system around HD169830 has been announced during the XIX-th IAP Colloquium "Extrasolar Planets: Today & Tomorrow" (Paris, June 30 - July 4, 2003) by the Geneva Extrasolar Planet Search team. We study the orbital dynamics of this system in the framework of the $N$-body problem. The analysis of its orbital stability is performed using the long-term integrations and the fast indicators, the Mean Exponential Growth factor of Nearby Orbits and the Frequency Map Analysis. The HD169830 appears to be located in a wide stable region of the phase space. The ratio of the mean motions of the planets HD169830b and c is between low-order mean motion resonances, 9:1 and 10:1. The long-term integration of the coplanar configurations, conducted over 1Gyr, reveals that the eccentricities of the companions vary with a large amplitude about 0.4-0.5 but there is no sign of instability. The orbital parameters of the planets resemble those of another 2-planetary system, around HD12661. Both of them can be classified as hierarchical planetary systems. We investigate whether these two exosystems are dynamically similar. Such similarities may be important for finding out if the formation and subsequent orbital evolution of exoplanetary systems obey common rules.Comment: 24 pages, 13 figures, 3 tables, submitted to ApJ. The preprint with high resolution figures is available from http://www.astri.uni.torun.pl/~chris/ms.ps.g