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

Masses and orbital inclinations of planets in the PSR B1257+12 system

We present measurements of the true masses and orbital inclinations of the two Earth-mass planets in the PSR B1257+12 system, based on the analysis of their mutual gravitational perturbations detectable as microsecond variations of the arrival times of radio pulses from the pulsar. The 6.2-millisecond pulsar, PSR B1257+12, has been regularly timed with the Arecibo telescope since late 1990. Assuming the standard pulsar mass of 1.4 M_Sun, the derived masses of planets B and C are 4.3 +/- 0.2 M_Earth and 3.9 +/- 0.2 M_Earth, respectively. The corresponding orbital inclinations of 53.4 and 47.3 deg (or 127 and 133 deg) imply that the two orbits are almost coplanar. This result, together with the known near 3:2 resonance between the orbits of the two planets, strongly supports the hypothesis of a disk origin of the PSR B1257+12 planetary system. The system's long-term stability is guaranteed by the low, Earth-like masses of planets B and C.Comment: 2 figures, to appear in ApJ

Radial velocity measurements of a sample of K-giants with the Hobby-Eberly telescope

We present motivation and initial results of a large RV survey of K giants aimed at a detection of low-mass companions. The survey, performed with the Hobby-Eberly Telescope, utilizes high resolution (60,000) spectra for high precision radial velocity measurements. The primary goal of the survey is the selection of astrometrically stable reference stars for the Extrasolar Planet Interferometric Survey key project to be carried out with the Space Interferometry Mission

Orbital solutions to the HD160691 (mu Arae) Doppler signal

We perform a dynamical analysis of the recently updated set of the radial velocity (RV) measurements of the HD160691 (mu Arae). The kinematic, 2-Keplerian model of the measurements leads to the best-fit solution in which the eccentricity of the outer planet is about 0.7 and its semi-major axis is about 4AU. The parameters of the inner planet are well determined. The eccentricity is about 0.3 and the semi-major axis is about 1.65AU. The best 2-Keplerian model leads to a catastrophically unstable configuration, self disrupting in less than 20,000yr. To derive dynamically stable configurations which are simultaneously consistent with the RV data, we use the so called GAMP (Genetic Algorithm with MEGNO Penalty). Using this method, we derive meaningful limits on the parameters of the outer planet which provide a stable behavior of the system. The best-fit solutions are located in a shallow valley of Chi^2, in the (a_c,e_c)-plane, extending over 2AU (for the formal 1sigma confidence interval of the best fit). We find two equally good best-fit solutions leading to the qualitatively different orbital configurations. One of them corresponds to the center of the 5:1 mean motion resonance (MMR) and the second one describes a configuration between the 6:1 and 17:2MMRs. The mu Arae system can be found in the zone confined to other low-order MMRs of the type p:1 with p>5. Our results support the classification of the mu Arae as a hierarchical planetary system, dynamically similar to other known multi-planet systems around HD12661 and HD169830. The results of the GAMP on the extended data set are fully consistent with our previous conclusions concerning a much shorter observational window.Comment: 6 pages, 1 table, 13 figures in low resolution suitable for astro-ph. Submitted to Ap

Tidal interactions of close-in extrasolar planets: the OGLE cases

Close-in extrasolar planets experience extreme tidal interactions with their host stars. This may lead to a reduction of the planetary orbit and a spin-up of stellar rotation. Tidal interactions have been computed for a number of extrasolar planets in circular orbits within 0.06 AU, namely for OGLE-TR-56 b. We compare our range of the tidal dissipation value with two dissipation models from Sasselov (2003) and conclude that our choices are equivalent to these models. However, applied to the planet OGLE-TR-56 b, we find in contrast to Sasselov (2003) that this planet will spiral-in toward the host star in a few billion years. We show that the average and maximum value of our range of dissipation are equivalent to the linear and quadratic dissipation models of Sasselov (2003). Due to limitations in the observational techniques, we do not see a possibility to distinguish between the two dissipation models as outlined by Sasselov (2003). OGLE-TR-56 b may therefore not serve as a test case for dissipation models. The probable existence of OGLE-TR-3 b at 0.02 AU and the discovery of OGLE-TR-113 b at 0.023 AU and OGLE-TR-132 b at 0.03 AU may also counter Sasselovs (2003) assumption of a pile-up stopping boundary at 0.04 AU.Comment: 7 pages, 4 figure

Stellar Astrophysics with a Dispersed Fourier Transform Spectrograph. II. Orbits of Double-lined Spectroscopic Binaries

We present orbital parameters for six double-lined spectroscopic binaries (iota Pegasi, omega Draconis, 12 Bootis, V1143 Cygni, beta Aurigae, and Mizar A) and two double-lined triple star systems (kappa Pegasi and eta Virginis). The orbital fits are based upon high-precision radial velocity observations made with a dispersed Fourier Transform Spectrograph, or dFTS, a new instrument which combines interferometric and dispersive elements. For some of the double-lined binaries with known inclination angles, the quality of our RV data permits us to determine the masses M_1 and M_2 of the stellar components with relative errors as small as 0.2%.Comment: 41 pages, 8 figures, accepted by A

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

Frequency Analysis of Reflex Velocities of Stars with Planets

Since it has become possible to discovery planets orbiting nearby solar-type stars through very precise Doppler-shift measurements, the role of methods used to analyze such observations has grown significantly. The widely employed model-dependent approach based on the least-squares fit of the Keplerian motion to the radial-velocity variations can be, as we show, unsatisfactory. Thus, in this paper, we propose a new method that may be easily and successfully applied to the Doppler-shift measurements. This method allows us to analyze the data without assuming any specific model and yet to extract all significant features of the observations. This very simple idea, based on the subsequent subtraction of all harmonic components from the data, can be easily implemented. We show that our method can be used to analyze real 16 Cygni B Doppler-shift observations with a surprising but correct result which is substantially different from that based on the least-squares fit of a Keplerian orbit. Namely, using frequency analysis we show that with the current accuracy of this star's observations it is not possible to determine the value of the orbital eccentricity which is claimed to be as high as 0.6.Comment: AASLaTeX + 5 figures (eps files), 22 pages, two figures delated, typos corrections; accepted for publication in Ap